Abstracts

Laboratorio Botanica marina, Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Ancona, Italy.

The role of sea temperature in Ostreopsis cf. ovata bloom dynamics along the Northern Mediterranean coast

Ostreopsis cf. ovata is a toxin-producing benthic dinoflagellate responsible for harmful blooms that impact marine ecosystems, coastal economies, and human health. Initially reported in tropical regions, it is now widespread across the Mediterranean, where it can reach high abundances during summer and autumn.
This study analyzes monitoring data (2010–2023) from the northwestern Mediterranean, including the coasts of Spain, France, Monaco, and Italy. O. cf. ovata is now firmly established across the region, showing stable persistence at historically colonized sites, both as an epiphyte and in the plankton.
Sea surface temperatures during bloom occurrence ranged from 15.5 to 34.8 °C. However, clear temperature–abundance relationships were detected at only 23% of stations, indicating a limited and site-dependent role of temperature. Temporal trends in abundance, bloom onset, and duration were observed at selected sites, but with contrasting patterns.
Overall, while rising sea temperatures may modulate O. cf. ovata bloom dynamics, the species response is highly heterogeneous and strongly controlled by local environmental conditions. Despite ongoing warming in the Mediterranean, bloom patterns appear largely stabilized across most monitored sites.

Second Institute of Oceanography, Ministry of Natural Resources of the People's Republic of China, Zhe Jiang Province, China.

Pengbin Wang*, Zihan Sun, Jiarong Hu, Lu Sun, Ruifang Wang, Ruoyu Guo, Jiraporn Charoenvattanaporn, Douding Lu, Myung-Soo Han

Taxonomy, composition, distribution pattern and toxicity of Prorocentrum (Dinophyceae) in East Asia

Prorocentrum, a cosmopolitan dinoflagellate genus with over 80 species globally, is a primary causative agent of harmful algal blooms (HABs), with many species producing diarrhetic shellfish poison (DSP) that bioaccumulates through marine food webs and poses human health risks. This study investigated the taxonomy, composition, distribution patterns, and toxicity of Prorocentrum species in East Asian coastal waters by collecting surface water and benthic samples from the East Asia. Over ninety strains were isolated and cultured stably, with morphological characterization employing light microscopy, confocal microscopy, and scanning electron microscopy, while molecular identification utilized specific gene amplification and sequencing. Fourteen Prorocentrum species were confirmed: P. concavum, P. donghaiense, P. elegans, P. fukuyoi, P. koreanum, P. lima, P. maculosum, P. micans, P. minimum, P. rhathymum, P. sculptile, P. sinense, and P. triestinum, with P. sculptile representing a new record for Chinese waters and P. koreanum and P. sinense identified as a new species. Additionally, biogeographic distribution patterns were preliminarily established, contributing to global distribution understanding and providing essential data for marine biodiversity research, ecosystem health maintenance, and HAB monitoring systems in this economically important marine region.

University of Nottingham, School of Bioscience, Nottingham, England.

Genetic modification in dinoflagellates algae

The ability to manipulate genomes, by inserting, knocking out or editing genes is a fundamental tool in modern bioscience research. Yet these tools are substantially missing for dinoflagellate algae, severely hampering our ability to study many ecologically important processes. This talk will address some of the progress (both successes and failures) that has been made by many groups in recent years. I will also speak about our attempts to establish stable genetic tools in two species, Symbiodinium microadriaticum and Amphidinium carterae. We have established tools for the manipulation of the A. carterae chloroplast genome, expressing a selectable marker and a heterologous protein of interest. In parallel, we have developed tools to insert a selectable marker and GFP to the mitochondrial genome of both A. carterae and S. microadriaticum. Protein expression is confirmed by Western blot. Genetically modified strains are stable, and have survived in the laboratory for many months. With these tools, we can begin to answer important biochemical questions, and to deepen our understanding of these enigmatic algae.

Department of Biochemistry, Cambridge, England.

Spontaneous Evolution of Heterotrophy in Dinoflagellates - Minicircle Loss in Symbiodinium microadriaticum

In assessing the evolutionary history of dinoflagellates, it is striking that there have been numerous losses and, in some cases, subsequent gain of photosynthetic capability. Photosynthetic dinoflagellates that contain peridinin as their principle accessory pigment possess a high reduced and also fragmented chloroplast genome. Instead of having chloroplast genes present on a single 120–200 kb DNA molecule, the dinoflagellate chloroplast genome is made up of multiple plasmid-like minicircles, typically 2–5 kbp, which are located in the chloroplast. Each minicircle carries one or a few genes as well as a “core” region containing the origin of replication. Having spent many years elucidating this unusual genome organisation, we reasoned that the loss of individual minicircles containing key photosynthesis genes might result in loss of photosynthetic capability and a switch to heterotrophy. We have been able to observe this occurrence under laboratory conditions. We found that growing the dinoflagellate Symbiodinium microadriaticum (a strain able to form symbioses with corals and other Cnidaria) on medium supplemented with glucose and amino acids allowed the ready isolation of multiple strains with spontaneous partial or complete loss of photosynthetic growth, resulting from the loss of a minicircle. Different strains showed independent loss of a minicircle encoding one of the PSII components PsbE or PsbI. Spectroscopic analysis confirmed loss/impairment of PSII and retention of PSI and cyclic electron flow CEF, probably providing ATP.

Ocean Sciences Dept., University of California, Santa Cruz, USA.

Novel Applications of Solid-phase Adsorption Toxin Tracking for Monitoring Harmful Algal Blooms

Solid-phase adsorption toxin tracking (SPATT) is a passive sampling method for monitoring dissolved toxins and other compounds. It has gained global popularity due to its high sensitivity, low-cost, and ease of use. This talk will overview traditional and novel applications of SPATT from a HAB monitoring perspective. On the California coast, SPATT is routinely deployed to monitor domoic acid, which causes Amnesiac Shellfish Poisoning (ASP). We developed new methodology in line with the existing protocols to measure a group of copepod exudates called copepodamides. Copepodamides are known to induce domoic acid production in Pseudo-nitzschia diatoms, but grazer effects are rarely considered in monitoring efforts. The inclusion of copepodamides measured over 28 weeks improved HAB predictions in empirical models, suggesting utility for including top-down information in HAB monitoring. We also used archived SPATT extracts to explore environmental metabolomics during recent toxin events in Monterey Bay using untargeted mass spectrometry. Results emphasized the interdisciplinary complexity of HAB drivers and encourage ongoing efforts to elucidate microbial interactions related to toxin production. Collectively, these projects expand the breadth of information that can be included in future HAB monitoring programs using passive chemical sampling.

School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.

Inter-partner communication and regulation in the cnidarian-dinoflagellate symbiosis

The cnidarian-dinoflagellate symbiosis is of huge ecological importance as it underpins the success of coral reefs, yet we know very little about how the host cnidarian and its dinoflagellate endosymbionts interact with each other to form a functionally integrated unit, and how biomass of the two partners is regulated to ensure homeostasis and symbiosis stability. Here, I will describe our work with the sea anemone Exaiptasia diaphana (‘Aiptasia’) – a globally-adopted model system for the study of the cnidarian-dinoflagellate symbiosis – aimed at clarifying how the host cnidarian regulates its symbiont population. We focused on symbiont cell-cycle arrest, host apoptosis and autophagy, and symbiont cell expulsion. We measured these in response to both the native symbiont of Aiptasia, Breviolum minutum, as well as several non-native symbiont species - Symbiodinium microadriaticum, Cladocopium goreaui and Durusdinium trenchii - and then applied a range of complex mathematical models to determine the relative importance of the various mechanisms involved. This approach revealed that symbiont cell-cycle arrest is the primary means by which the symbiont population is controlled, though the other mechanisms, and apoptosis especially, all play an important part at different stages of symbiosis establishment and maintenance. Furthermore, while there were commonalities between the responses to the different dinoflagellate species, D. trenchii was notable in that its proliferation was less tightly regulated than the other symbionts and it induced an earlier depression of host apoptosis. This latter is finding is especially interesting given that D. trenchii is known to be an opportunistic, nutritionally selfish partner. I will end the seminar by briefly exploring this latter point, giving an overview of some of my group’s other work, where we apply a range of omics (esp. proteomics and metabolomics), imaging mass spectrometry and immunocytochemistry techniques to understand how the host and symbiont communicate and interact with one another, and how this is impacted by symbiont identity, thereby driving patterns of host-symbiont specificity.

Cawthron Institute, New Zealand.

Alexandrium pacificum: From Ecological Challenge to Biomedical Opportunity

^{Hannah Greenhough 1,2, Craig Waugh 1, Roel van Ginkel 1, Joel Bowate r1, Gurmeet Kaur 1, Joy Oakly 1, Maxence Plouviez 1, Richard A. Ingebrigtsen 1, Johan Svenson 1, Andrew I Selwood 1, Kirsty F Smith 1, Chris M Brown 2, Julien Vignie r1, Nathan J Kenny 2, Anne Rolton 1}

Marine microalgal toxins present opportunities for drug discovery but also pose substantial risks to aquaculture and coastal environments. The dinoflagellate Alexandrium pacificum produces paralytic shellfish toxins (PSTs), highly potent blockers of voltage-gated ion channels and promising candidates for drug development. Their complex chemistry and limited natural availability have constrained wider application, but recent advances in large-scale cultivation of A. pacificum have enabled gram-scale production of gonyautoxins, providing new opportunities for pharmaceutical and research applications.
In parallel, A. pacificum blooms pose significant challenges to aquaculture. In Aotearoa New Zealand, harmful algal blooms impact the green-lipped mussel (Perna canaliculus), a species of high economic, ecological, and cultural value. Experimental exposures to A. pacificum showed that early life stages are particularly sensitive, with mussel sperm mortality, embryo lysis, and up to 85% reductions in larval development at cell concentrations found in natural blooms. Later stages exhibit impaired growth, reduced attachment, and stress responses involving oxidative damage and immune suppression. These effects are further compounded when blooms coincide with marine heatwaves, intensifying impacts on mussel survival and recruitment.
Together, these findings highlight the contrasting impacts of A. pacificum. On one hand, its toxins represent valuable pharmacological tools with potential to drive drug discovery and biomedical innovation. On the other, the same compounds and associated bloom events disrupt mussel development, compromise aquaculture production, and threaten the resilience of coastal ecosystems. Recognising both the opportunities and risks of A. pacificum is essential for realising the biomedical potential of PSTs while developing strategies to protect aquaculture and coastal ecosystems under future climate change.

Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.

Quantitative molecular diversity and evolution of ribosomal genes in dinoflagellates

Metabarcoding technology has been widely applied to probe the diversity and dynamics of dinoflagellates, some protists can develop harmful algal blooms (HABs) with negative impact on marine ecosystems worldwide. Although metabarcoding analysis is effective in characterizing protist biodiversity and spatiotemporal dynamics with high resolution, being able to identify dinoflagellates that could not be properly identified using morphology-based approaches because some are too small in cell sizes, too similar in cell morphologies, and too fragile in sample fixation, accurate identification of individual species from mountains of sequences remains challenging. Inaccurate interpretation of sequences obtained in metabarcoding analysis can lead to the overestimation and even erroneous identification of biodiversity of marine ecosystems. To address this problem, the molecular marker 18S rDNA V4 that has been a common molecular marker used in metabarcoding analyses of single cells or single strains of a few representative dinoflagellate HAB species (including the dinoflagellate Noctiluca scintillans and Tripos species) were sequenced and analyzed to examine the nature of molecular diversity revealed in metabarcoding analyses. Each single cell was found to harbor a large number of variants with different relative abundances, with usually a few dominant variants and many non-dominant variants, indicating high intra-genomic variations (IGVs). Different cells of a particular species usually share the dominant variant, but not always. Some variants were found to be the dominant variants of one species, but non-dominant variants in other species of the same genus. Thus, proper understanding of the nature of molecular diversity of molecular marker is critical for extracting species and genetic diversity information.

Autonomous Metropolitan University, Mexico City, Mexico.

Uriel T. Ruíz-García¹, María Luisa Núnez-Resendiz², María Eugenia Zamudio-Resendiz², Yuri B. Okolodkov³

Recent progress and emerging tools in athecate dinoflagellate classification and phylogeny

^{1 Master's degree in Biology, Department of Hydrobiology, Autonomous Metropolitan University, Mexico City, 09340, Mexico
2 Area ofComparative Phycology, Department of Hydrobiology, Autonomous Metropolitan University, Mexico City, 09340, Mexico
3 Marine Botany and Planktology laboratory, Institute of Marine Sciences and Fisheries, Universidad Veracruzana, Veracruz, 94294, Mexico}

Dinoflagellates without cellulose in the cortical alveoli represent a diverse and complex group of organisms. Their fragility during fixation, complex life cycles, and difficulty in cultivating some species, coupled with the absence of stable morphological characters across higher taxa, have made their study a slow process compared to the much more studied thecate dinoflagellates. Traditional taxonomy has focused on variable characteristics such as the position of the cingulum and the number of turns around the cell, plastid types, nucleus position, and, more recently, the shape of the apical groove, which is stable enough for phylogenetic reconstruction in a handful of cases. The advent of molecular phylogeny has helped begin uncovering the diversity and relationships between groups beyond what a morphological approach has allowed. From molecular analyses it has been found that the largest group within the free-living athecate dinoflagellates, the Gymnodiniales, is polyphyletic and has been split into multiple groups, such as the Amphidiniales, Suessiales, Tovelliales, and many groups of uncertain placement. The absence of genetic sequences in GenBank complicates the evolutionary reconstruction and taxonomic classification of species. However, new studies are constantly providing new data that will allow for a more robust reconstruction of the phylogeny.

Bachok Marine Research Station, IOES, University of Malaya, Malaysia.

Diversity of tropical benthic harmful dinoflagellates: integrating molecular and morphological analyses with natural and artificial substrate sampling methods

^{C.P. Leaw1, N.S. Kassim1, K.S. Hii1, S.T. Teng2, K. Mertens3, M. Iwataki4, H. Gu5, P.T. Lim1}

^{1 Bachok Marine Research Station, IOES, University of Malaya, Malaysia
2 Universiti Malaysia Sarawak, Malaysia
3 Ifremer, France
4 University of Tokyo, Japan
5 Third Institute of Oceanography, China}

Harmful algal blooms in the benthic system (BHAB) are a major environmental problem that has increased worldwide. While systematic cell-based BHAB monitoring for risk assessment and early warning systems have been recommended, implementation of a standardized sampling method is challenging owing to the benthic nature of these harmful microalgal taxa. This presentation will explore findings from recent studies1,2 that combine morphological and molecular analyses to assess the diversity of benthic harmful dinoflagellates in tropical reefs. The study focuses on the comparative efficacy of artificial versus natural substrate sampling methods in capturing benthic harmful dinoflagellates using DNA metabarcoding. The universal rDNA barcodes enabled fine-resolution detection of BHAB taxa, particularly Gambierdiscus and Ostreopsis, which are challenging to identify by light microscopy. Further, the approach allowed precise identification of the toxic ribotypes of O. cf. ovata. The findings demonstrate the potential of integrating these methods for improved monitoring.

To cite:

1. Kassim NS, Lee LK, Hii KS, Mohd Azmi NF, Baharudin SN, Liu M, Gu H, Lim PT, Leaw CP. 2025. Molecular diversity of benthic harmful dinoflagellates on a tropical reef: Comparing natural and artificial substrate sampling methods using DNA metabarcoding and morphological analysis. Harmful Algae 142: 102795.
2. Gu H, Wang Y, Derrien A, Hervé F, Wang N, Pransilpa M, Lim PT, Leaw CP. 2022. Two toxigenic Ostreopsis species, O. cf. ovata and O. siamensis (Dinophyceae), from the South China Sea, tropical Western Pacific. Harmful Algae 113: 102206.

Department of Earth Sciences, Laboratory of Palaeobotany and Palynology, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands.

Appy Sluijs1 and Henk Brinkhuis1,2

High Arctic late Paleocene and early Eocene dinoflagellate cysts

<sup>1. Department of Earth Sciences, Laboratory of Palaeobotany and Palynology, Faculty of Geosciences, Utrecht University, 3584 CB Utrecht, the Netherlands
2. Department of Ocean Systems (OCS), Royal Netherlands Institute for Sea Research (NIOZ), PO Box 1790 AB Den Burg, the Netherlands</sup>

Palynomorphs, notably sporomorphs and organic-walled dinoflagellate cysts, or “dinocysts”, are the only abundant microfossils consistently present in the sole available central Arctic upper Paleocene to lower Eocene sedimentary succession recovered at the central Lomonosov Ridge by the Integrated Ocean Drilling Program (IODP) Expedition 302 (or the Arctic Coring Expedition, ACEX) in 2004, close to the North Pole. While the analysis and interpretation of a part of these assemblages have so far guided many major stratigraphic, climatological, and paleoenvironmental findings from ACEX, intrinsic details, notably of the dinocyst taxa and assemblages, have not yet been addressed. Here, we present new ACEX dinocyst data for the interval spanning the latest Paleocene to the earliest Eocene (∼56.5–53.8 Ma; cores 32X–27X) and integrate these with previous results. We develop a pragmatic taxonomic framework, document critical biostratigraphic events, and propose two new genera (Guersteinia and Sangiorgia) and seven new species (Batiacasphaera obohikuenobeae, Chaenosphaerula sliwinskae, Heterolaucacysta pramparoae, Pyxidinopsis iakovlevae, Sangiorgia pospelovae, Sangiorgia marretiae, and Spiniferella crouchiae). In addition, we interpret trends and aberrations in dinocyst assemblages in terms of variability in regional temperature, hydrology, and tectonism across the long-term and the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2) global warming phases.

How to cite: Sluijs, A. and Brinkhuis, H. 2024: High Arctic late Paleocene and early Eocene dinoflagellate cysts, J. Micropalaeontol., 43, 441–474, https://doi.org/10.5194/jm-43-441-2024

Tohoku University, Japan.

Y. Cho 1, S. Hidema 2, T. Omura 3, K. Koike 4, K. Koike 5, S. Tsuchiya 1, K. Konoki 1, Y. Oshima 6#, M. Yotsu-Yamashita 1

Saxitoxin biosynthesis and metabolism in dinoflagellates as revealed by metabolic fluxes analysis and studies of early biosynthetic enzymes

^{1Graduate School of Agricultural Science, Tohoku University, Sendai, Japan
2Fukushima Medical University, Fukushima, Japan
3Tokyo University of Marine Science and Technology, Tokyo, Japan
4Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, Japan
5Natural Science Center for Basic Research and Development Hiroshima University, Higashi-Hiroshima, Japan
6Graduate School of Life Sciences, Tohoku University, Sendai, Japan
# Proffesor emeritus
yuko.cho.a4@tohoku.ac.jp}

Saxitoxin (STX) and its analogues are collectively known as paralytic shellfish toxins (PSTs) and are causative agents of paralytic shellfish poisonings. Because these are potent inhibitors of voltage-dependent sodium channels, consuming shellfish contaminated with PSTs can cause food poisoning. The genuine producers of PSTs are various species of marine dinoflagellates (the genera Alexandrium, Pyrodinium and Gymnodinium). The harmful blooms of PST-producing dinoflagellates are found throughout the world and caused serious threats to human health. To develop strategies to predict changes in risk, it is important to elucidate the mechanisms of STX biosynthesis and metabolism. The STX biosynthesis gene clusters (a total of 21 genes) have been identified in another STX producing organism, cyanobacteria. Based on the putative function of these genes and identification of intermediates, the STX biosynthetic pathway was proposed1, 2. However, STX biosynthesis in dinoflagellates have not yet been fully elucidated, because of the unique characteristics of dinoflagellates, such as large genome size, high gene copy number and un-clustered arrangement of genes. Only five putative genes have thus far been reported as full-length sequences in dinoflagellates (sxtA, sxtG, sxtB, sxtI, and sxtU). We are trying to approach the issue from various aspects. By the isotope assisted metabolic flux analysis of STX related compounds (precursors, intermediates and STXs): in vivo labeling method, we proposed the hypothesis that STXs are biosynthesized through de novo and salvage biosynthesis3, 4. Furthermore, we have been focusing on the key enzymes, SxtA and SxtG, that catalyze early steps among STX biosynthetic enzymes. The analysis of abundance and localization of them revealed that SxtA and SxtG are expressed in chloroplasts and the absence of SxtA leads to loss of toxin producibility in the non-toxic subclone of Alexandrium catenella (Group I) 5, 6. The methods we have developed will be useful for elucidating the biosynthesis and metabolism of STX in dinoflagellates, for which conventional genetic engineering methods are not suitable.

References

1. Tsuchiya, S.; Cho, Y.; Yoshioka, R.; Konoki, K.; Nagasawa, K.; Oshima, Y.; Yotsu-Yamashita, M. Angew. Chem. Int. Ed. 2017, 56, 5327–5331.
2. Hakamada, M.; Tokairin, C.; Ishizuka, H.; Adachi, K.; Osawa, T.; Aonuma, S.; Hirozumi, R.; Tsuchiya, S.; Cho, Y.; Kudo, Y.; Konoki, K.; Oshima, Y.; Nagasawa, K.; Yotsu‐Yamashita, M. Chem. Euro. J. 2024, 30, e202304238.
3. Cho, Y.; Tsuchiya, S.; Omura, T.; Koike, K.; Oikawa, H.; Konoki, K.; Oshima, Y.; Yotsu-Yamashita, M. Sci Rep., 2019, 9, 3460.
4. Cho, Y.; Tsuchiya, S.; Omura, T.; Koike, K.; Konoki, K.; Oshima, Y.; Yotsu-Yamashita, M. Harmful Algae 2023, 122, 102372.
5. Cho, Y.; Hidema, S.; Omura, T.; Koike, K.; Koike, K.; Oikawa, H.; Konoki, K.; Oshima, Y.; Yotsu-Yamashita, M. Harmful Algae 2021, 101, 101972.
6. Cho, Y.; Hidema, S.; Omura, T.; Tsuchiya, S.; Konoki, K.; Oshima, Y.; Yotsu-Yamashita, M. Harmful Algae 2024, 139, 102723.

Department of Biology,
Woods Hole Oceanographic Institution (WHOI), Woods Hole, Massachusetts, USA.

Sylvain Gaillard^a,b, Hamish J. Smal^la, Nour Ayache^b, Simon Tanniou^c, Philipp Hess^c, Damien R ́eveillon^c, Constance M. Harris^d, Thomas M. Harris^d, Gail P. Scott^a, Alanna MacIntyre^a, Kimberly S. Reece^a

Assessment of allelochemical interactions between Alexandrium monilatum and other phytoplankton species

^{a Virginia Institute of Marine Science, William & Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA
b Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
c IFREMER, PHYTOX unit, F 44000 Nantes, France
d Department of Chemistry, Vanderbilt University, Nashville, TN, 37235, USA}

Species of Alexandrium can release bioactive extracellular compounds with allelopathic effects on other phytoplankton. The goniodomin producer Alexandrium monilatum forms blooms in the lower Chesapeake Bay, Virginia, US, that co-occur along with or immediately following a bloom of the dinoflagellate Margalefidium polykrikoides, which are often preceded by blooms of the dinoflagellate Akashiwo sanguinea. However, the allelopathic potential of A. monilatum and how it may affect bloom dynamics have not been studied. Using a rapid fluorescence-based bioassay, flow cytometry, and an assessment of immobilization, we determined the effects of A. monilatum culture supernatants and standards of goniodomins on M. polykrikoides, A. sanguinea, and the diatom Chaetoceros muelleri (included as a reference strain). We observed strain-specific effects of the activity on the maximum quantum yield of the photosystem II (Fv/Fm), the morphology, and the mortality of the diatom, as well as a negative effect on the motility of M. polykrikoides, while no effect was observed on A. sanguinea. The study of supernatant time- and temperature-stability, and the absence of a relationship between observed effects and goniodomin concentrations suggested the presence of additional unknown allelochemicals distinct from goniodomins. While A. monilatum is capable of allelopathic interactions in laboratory-based assays, proving the competitive advantage over M. polykrikoides in the environment will require further studies, which will provide a better understanding of the bloom dynamics of these dinoflagellates in the Chesapeake Bay.

Distinguished Professor, Earth Sciences, Brock University, Canada.

Head, Martin J.1

Dual nomenclature in organic-walled dinoflagellate cysts: a new concept for the Code

_{1. Department of Earth Sciences, Brock University, Canada.}

For the first time, dual nomenclature in dinoflagellates is to be supported explicitly under the International Code of Nomenclature for algae, fungi and plants: the new Madrid Code to be published in mid-2025 (Head et al., 2024a). Dual nomenclature is underpinned by conceptual and practical considerations. It allows the separate naming of fossil- and non-fossil species even when they are linked to one another by incubation studies and other techniques (Head et al., 2024b, 2024c). It is needed because fossil- and non-fossil taxonomies are based on different stages of the life cycle and cannot be integrated at the generic level. All taxonomists today who study dinoflagellates, whether living or fossil, place their work under the Code. The Shenzhen Code and its predecessors have supported dual nomenclature implicitly with the help of examples, but without clear explanation of what it is and how it works. In Madrid, Spain, in July 2024, the Nomenclature Section of the XX International Botanical Congress approved two new articles for the Code that remove earlier contradictions and introduce dual nomenclature explicitly, drawing on a critical distinction between ‘synonymy’ and the new concept and term ‘taxonomic equivalence’ (Head et al., 2024a). Examples using Lingulodinium machaerophorum (Deflandre & Cookson 1955) Wall 1967 and its taxonomic equivalent Lingulaulax polyedra (von Stein 1883) Head et al. 2024c, and Spiniferites elongatus and Spiniferites membranaceus and their taxonomic equivalents Gonyaulax ovum (Gaarder 1954) Head et al. 2024d and Gonyaulax lewisiae Head et al. 2024d, are discussed, crucially along with the nomenclatural criteria used to distinguish between a fossil and a non-fossil specimen.

Editorial comment (Marc Gottschling)

Time is not on the side of dual nomenclature.

The preamble of the Botanical Code reads: ‘Biology requires a precise and simple system of nomenclature ... The purpose of giving a name to a taxonomic group is ... to supply a means of referring to it ... Next in importance is the avoidance of the useless creation of names’, and principle IV reads: ‚Each taxonomic group ... can bear only one correct name, the earliest that is in accordance with the rules ...‘. Dual nomenclature as presented by Martin J. Head cannot be harmonised with these aims. This has already become clear from a decades-long discussion about the schism within the fungi, whereby teleomorph and anamorph had different names. It was generally seen as a major step forward in the previous Code that this schism had been overcome and that the 1-organism-1-name concept was now also being adopted for fungi. Feasibly, flagellated and coccoid stages of dinophytes can be integrated, and arguing the converse ignores the decades of diligent work by numerous colleagues. The normal and proven procedure to change the Code is to write a proposal, have it thoroughly reviewed by the respective Special Committees, receive a critical opinion from it and finally vote on it at a Botanical Congress held every five years – none of this has happened in this case. If these rules come into force, they will complicate, not facilitate, the intended aim of the Code: the best possible scientific communication about individual species. These new rules divide the community of biological and palaeontological scientists instead of bridging gaps and effectively advancing a unified naming of species and species groups.

References

Head, M.J., Gravendyck, J., Herendeen, P.S., Turland, N.J., 2024a. Dual nomenclature to be supported explicitly in the International Code of Nomenclature for algae, fungi, and plants. Palynology [Publication September–October 2024].

Head, M.J., Fensome, R.A., Mertens, K.N., and Herendeen, P.S., 2024b. Critique of Proposals 258–260 to eliminate contradiction between Articles 11.7 and 11.8 and to equate non-fossil with fossil names of dinophytes for purposes of priority, by Elbrächter & al. (2023), and ensuing recommendations. TAXON, 73(1): 405–407.

Head, M.J., Mertens, K.N., and Fensome, R.A., 2024c. Dual nomenclature in organic-walled dinoflagellate cysts I: concepts, methods and applications. Palynology 48, No. 2, 2290200.

Head, M.J., Mertens, K.N., and Fensome, R.A., 2024d. Dual nomenclature in organic-walled dinoflagellate cysts II: Spiniferites elongatus Reid 1974 and S. membranaceus (Rossignol 1964) Sarjeant 1970, and their equivalent non-fossil species Gonyaulax ovum (Gaarder 1954) comb. nov. and G. lewisiae sp. nov. Palynology 48, No. 2, 2300838.

Aquatic Ecology Unit, Department of Biology, Lund University, Sweden.

Rengefors, Karin1

Population genomic analyses reveal that salinity and geographic isolation drive diversification in a free‑living protist

_{1. Aquatic Ecology Unit, Department of Biology, Lund University, Sweden.}

Species diversity, distribution and delimitation is challenging in most protists including dinoflagellates. Moreover, because of their small size, cryptic life cycles, and large population sizes, our understanding of speciation in these organisms is very limited. We performed population genomic analyses on 153 strains isolated from eight populations of the recently radiated dinoflagellate genus Apocalathium, to explore the drivers and mechanisms of speciation processes. Species of Apocalathium (previously Peridinium and Scrippsiella) inhabit both freshwater and saline habitats, lakes and seas, and are found in cold temperate environments across the world. RAD sequencing analyses revealed that the populations were overall highly differentiated, but morphological similarity was not congruent with genetic similarity. While geographic isolation was to some extent coupled to genetic distance, this pattern was not consistent. Instead, we found evidence that the environment, specifically salinity, is a major factor in driving ecological speciation in Apocalathium. By coupling RAD sequencing and transcriptome analysis, we could determine that saline populations had unique in RAD-loci coupled to genes involved in osmoregulation, while freshwater populations appear to lack these. Our study highlights that adaptation to freshwater through loss of osmoregulatory genes may be an important speciation mechanism in free-living aquatic protists.

Royal Belgian Institute of Natural Sciences
OD Natural Environment, ATECO, Freshwater Biology, Brussels.

Isa Schön1,2, Yelle Vandenboer1 and Deborah Dupont1

eDNA and metabarcoding as new tool to monitor (toxic) phytoplankton

<sub>1. Royal Belgian Institute of Natural Sciences, OD Nature, ATECO, Freshwater Biology, Vautierstraat 29, 1000 Brussels,
Belgium ischoen@naturalsciences.be
2. Centre for Environmental Sciences, University of Hasselt, Agrolaan Building D, 3590 Diepenbeek, Belgium</sub>

The development of high throughput automatic DNA sequencing methods has led to an explosive growth of environmental DNA and metabarcoding studies. eDNA metabarcoding allows to study an entire community together and has been shown to be faster and cheaper than classic methods to characterize marine biodiversity. Here, we have applied eDNA metabarcoding to phytoplankton of the Belgian part of the North Sea. As part of the monthly monitoring campaigns of our institute, we collected and filtered water samples during 15 cruises with RV Belgica in 2022 and 2023 at three locations. We amplified and sequenced a longer part of 18S than in other studies by using Oxford Nanopore long read sequencing technology. Our approach was highly successful as we could identify phytoplankton taxa to the species level. With this fine resolution, we could unravel temporal and spatial patterns of phytoplankton diversity. Most toxic taxa could also be identified to the species level, allowing us to link their occurrence to potential negative effects. This kind of information is essential for aquaculture, fisheries and human recreation.

Horizontal Evolution of Algal Lifestyles (HEAL), Institut de Biologie, Paris.

Dorrell, Richard 1

The bizarre chloroplasts of dinoflagellate algae

_{1. Horizontal Evolution of Algal Lifestyles (HEAL), Institut de Biologie, Paris.}

"Every rule in eukaryotic cell biology is broken by dinoflagellates". But how does this maxim apply to their chloroplasts? In this short talk, I will outline work from my group over the past 15 years to explore the weirdness in dinoflagellate plastid evolution, considering their fragmented genomes, nucleus-encoded proteomes, and propensity for plastid loss and replacement via serial endosymbiosis. I will particularly discuss how Kareniaceaen dinoflagellates, which have replaced the ancestral peridinin plastid with a fucoxanthin-containing one of haptophyte origin, can act as models for how chloroplasts can and do evolve. This includes evidence for a much greater number of endosymbioses in the Kareniaceae than previously reported, with different species independently and repeatedly acquiring haptophyte chloroplasts, with different biological consequences in each case.

University of North Carolina at Charlotte, USA.

Erik L. J. E. Broemsen 1

Thermal ecotypes of Karlodinium veneficum as demonstrated through determination of division time (td) for in situ growth rate measurement

_{1. University of North Carolina at Charlotte}

The toxic dinoflagellate Karlodinium veneficum forms fish killing blooms in temperate estuaries worldwide. These blooms have variable toxicity which may be related to bloom stage and in situ growth rates of the constituent K. veneficum cells. Measurement of in situ growth rates is challenging and methods such as the mitotic index technique require knowledge of the dynamics of cell division. In order to better understand these dynamics, we determined the duration of cell division (td) in four geographically distinct laboratory strains of K. veneficum at three different environmentally relevant temperatures. The results demonstrated that the td value for each strain, growing at strain-specific optimal temperatures, was 1.6 ± 0.1 h. This value corresponded to a range of growth rates from 0.17 ± 0.08 d−1 to 0.62 ± 0.07 d−1. Equivalent values of td spread across four geographically distinct laboratory strains and a nearly fourfold range of growth rates implies that 1.6 h represents the td value of K. veneficum. Additionally, temperature conditions yielding this value for td and the highest growth rates varied among strains, indicating cold-adapted (Norway), warm-adapted (Florida, USA), and eurythermally-adapted (Maryland, USA) strains. These differences have been apparently retained in culture over many years, indicating a conserved genetic basis that suggests distinct thermal ecotypes of the morphospecies K. veneficum. This knowledge together with the first estimate of td for K. veneficum will be useful in future field studies aimed at correlating bloom toxicity with in situ growth rate using the mitotic index technique.

South China Sea Institute of Oceanology, Chinese Academy of Sciences, China.

Dajun Qiu 1*, Jingfu Chen 1, Yu Zhong 1, Lei Wang ₁

The diets of the bloom-forming dinoflagellate Noctiluca scintillans in situ

_{1. CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
*djqiu@scsio.ac.cn}

Red Noctiluca scintillans is a common heterotrophic dinoflagellate that forms blooms in temperate, subtropical, and tropical coastal ecosystems. The diet of this species plays an important role in its cell growth, development, and reproduction. Because limited gene diversity data are available regarding prey of this species, its diet in Daya Bay during a boreal winter bloom is reported using an integrated approach involving light microscopy, single cell isolation and plastid 16S rDNA cloning, and 18S rDNA V4 and V9 region amplification using isolated cells and environmental DNA as templates with high-throughput sequencing. While conventional light microscopy reveals the diet of this species to comprise Coscinodiscus sp. and Stephanopyxis turris (diatoms), copepod eggs, and detritus, plastid gene diversity identifies a diet comprising diatoms, cyanobacteria, and bacteria, and 18S rDNA high-throughput sequencing reveals a diet comprising 36 eukaryote families (primarily copepods, as well as diatoms, dinoflagellates, Ochrophyta, Haptophytes, Chordata, Cercozoans, Chlorophyta, Polychaeta, and ciliates). Dietary staples include copepods, diatoms, dinoflagellates, Ochrophyta, and Synechococcus. High copepod abundance in prey may reflect their relatively high abundance in environmental seawater. Thus, N. scintillans is generally omnivorous but prefers dominant phytoplankton taxa, including Rhizosoleniaceae, Leptocylindraceae, and Cymatosiraceae (diatoms), as well as Gonyaulacaceae (dinoflagellates). An integrated multi-disciplinary approach provides a more comprehensive picture of N. scintillans diet in Daya Bay, and an improved understanding of this species’ ecological niche and trophic role in marine ecosystems.

Marine and Freshwater Research Institute, Hafnarfjörður, Iceland.

Sara Harðardóttir 1,2,17, James S. Haile 3, Jessica Louise Ray 4, Audrey Limoges 1,5, Nicolas Van Nieuwenhove 1,5, Catherine Lalande 6, Pierre-Luc Grondin 6,7, Rebecca Jackson 1,3, Katrine Sandnes Skaa r4, Maija Heikkilä 8, Jørgen Berge 9,10, Nina Lundholm 11, Søren Rysgaard 12,13,14, Marit-Solveig Seidenkrantz 15, Stijn De Schepper 4,16, Eline D. Lorenzen 3, Guillaume Massé 2,7, Connie Lovejoy 2,7, Sofia Ribeiro1

Millennial-scale variations in Arctic sea ice are recorded in sedimentary ancient DNA of the microalga Polarella glacialis

^{1 Glaciology and Climate Department, Geological Survey of Denmark and Greenland, Copenhagen, Denmark.
2 Département de Biologie, Université Laval, Québec, Québec, Canada.
3 Globe Institute, University of Copenhagen, Copenhagen, Denmark.
4 NORCE Norwegian Research Centre AS, Climate & Environment Department, Bergen, Norway.
5 Department of Earth Sciences, University of New Brunswick, Fredericton, Canada.
6 Amundsen Science, Université Laval, Québec City, Canada.
7 Takuvik International Research Laboratory, Université Laval, Québec, Québec, Canada.
8 Helsinki Institute of Sustainability Science, University of Helsinki, Finland.
9 Department of Arctic and Marine Biology, UiT, The Arctic University of Norway, Tromsø, Norway.
10 Centre for Autonomous Marine Operations and Systems, Department of Biology, Norwegian University of Science and Technology, NTNU, Norway.
11 The Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark.
12 Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland.
13 Arctic Research Centre, Department of Biology, Aarhus University, Aarhus C, Denmark.
14 Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada.
15 Paleoceanography and Paleoclimate Group, Arctic Research Centre, and Climate Centre, Department of Geosciences, Aarhus University, Aarhus, Denmark.
16 Bjerknes Centre for Climate Research, Bergen, Norway.
17 Marine and Freshwater Research Institute. Hafnarfjörður, Iceland.}

Sea ice is a critical component of the Earth’s Climate System and a unique habitat. Sea-ice changes prior to the satellite era are poorly documented, and proxy methods are needed to constrain its past variability. Here, we demonstrate the potential of sedimentary DNA from Polarella glacialis, a sea-ice microalga, for tracing past sea-ice conditions. We quantified P. glacialis DNA (targeting the nuclear ribosomal ITS1 region) in Arctic marine and fjord surface sediments and a sediment core from northern Baffin Bay spanning 12,000 years. Sea ice and sediment trap samples confirmed that cysts of P. glacialis are common in first-year sea ice and sinking particulate matter following sea-ice melt. Its detection is more efficient with our molecular approach than standard micropaleontological methods. Given that the species inhabits coastal and marine environments in the Arctic and Antarctic, P. glacialis DNA has the potential to become a useful tool for circum-polar sea-ice reconstructions.

MARUM - Center for Marine Environmental Sciences, Bremen, Germany.

Roza, S. E. V .1, Zonneveld K. A. F. 1,2, Versteegh, G. J. M .3, Pospelova, V .4, Reuter, R. M .1, Stuut, J.- B. 5,6

Unveiling the recent climate change in the Northwest African Coast using time series analysis on dinocyst export production

_{1 MARUM - Center for Marine Environmental Sciences, Bremen, Germany
2 University of Bremen, Department of Geosciences, Bremen, Germany
3 Constructor University, Department of Physics and Earth Sciences, Bremen, Germany
4 University of Minnesota, Department of Earth and Environmental Sciences, Minneapolis, United States of America
5 NIOZ Royal Netherlands Institute for Sea Research, Department of Ocean Systems, Texel, Netherlands
6 Vrije Universiteit (VU) Amsterdam, Faculty of Earth and Life Sciences, Amsterdam, Netherlands}

The anthropogenic carbon contribution and consistent changes in nature have put a huge pressure on the sustainability of all ecosystems, and the ocean is no exception. Investigating high-resolution proxies for environmental reconstruction, such as marine plankton, is crucial to gaining better knowledge about the climate change. Therefore, we deliver a recent record of dinoflagellate cysts (dinocysts) from the coastal upwelling near Cape Blanc (Northwest Africa). Herein, the high plankton production (including dinoflagellates) is accommodated by the annual permanent upwelling and is supported by Saharan dust. Dinocysts were collected by a sediment trap from 2003 until 2020 with a resolution of one to three weeks. This data type is limited, and published studies focus more on the interannual production and ecology of the dinocyst taxa. Under the recent climate change scenario, we want to test the potential of the dinocyst record as a climate proxy. We executed dinocysts record and abiotic factors in this area, such as upwelling wind, dust emission, and sea surface temperature, with wavelet time series analysis to distinguish half-year and annual cycles in each dataset. Moreover, we observed three phases in the upwelling wind and dust emission cycles that also occurred in the dinocyst record. The annual cycle variations suggest a shift in the position of the Inter Tropical Convergence Zone (ITCZ), indicating changes in Northern/Southern hemisphere’s temperature.

LAMPEA, Aix-Marseille University, France.

Leroy, Suzanne 1,2,3 and Marret, Fabienne 3

Dinocyst assemblages in MIS 6 and MIS5 of the Sea of Marmara (Turkey) and similarities with the Caspian Sea

<sub>1. Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France, suzleroy@hotmail.com
2. Aix Marseille Univ, CNRS, Minist. Culture & Com., LAMPEA, 13094 Aix-en-Provence, France
3. School of Environmental Sciences, University of Liverpool, L69 7ZT Liverpool, UK</sub>

The Sea of Marmara (SoM) is the connection between the vast Black Sea-Caspian Sea basin (Pontocaspian) and the Global Ocean via the Mediterranean Sea. Its water levels and water conditions have widely varied over times. Combining two cores in the SoM and using organic-walled dinoflagellate cyst assemblages as the main proxy (combined with alkenones and benthic foraminifera), allow qualitatively reconstructing water conditions during Marine Isotopic Stage (MIS) 6 and 5, such as salinity and oxygen level. A clear main marine phase is illustrated in MIS 5e. A minor marine incursion occurred during MIS 5c, mostly supported by alkenone data. The rest of the record indicates brackish Pontocaspian conditions, with more Spiniferites inaequalis in MIS 6 and more S. cruciformis in the non-marine parts of MIS 5.
At the MIS 6/MIS 5 transition, an earlier initial marine flooding in the SoM (dinocyst assemblages) in comparison to the Black Sea was highlighted. The marine reconnection occurred at different moments as seen in the terrestrial vegetation reconstructed from pollen analysis linking the two seas.
Many dinocyst taxa newly identified in the Caspian Sea, such as Caspidinium rugosum and Impagidinium caspienense, were also found in the brackish phases of the SoM.

Marine Biological Section, University of Copenhagen, Denmark.

Acquired phototrophy in marine protists

Most marine biology text books still split marine planktonic protists into “animals” that feed, and “plants” that photosynthesize and take up inorganic nutrients. This is also how protists usually are dealt with in food web models. However, many protists are mixoplanktonic, i.e. they photosynthesize and engulf prey organisms. In this presentation, I will focus on mixotrophy in protists that lack chloroplasts of their own and thus are dependent on acquired phototrophy. Protists with acquired phototrophy are ubiquitous and can be found in eutrophic coastal waters as well as in oligotrophic oceanic waters. In some cases, they even form blooms or produce phycotoxins that accumulate in the marine food web. The group comprises of protists with endo- and ecto-symbionts as well as protists that sequester chloroplasts, and sometimes, other cell organelles from their prey. It is functionally a quite diverse group, which covers almost the entire mixotrophic spectrum from predominantly phototrophic to predominantly heterotrophic species. In this presentation, I will show examples of their functional biology and ecophysiology, and discuss their success in different habitats.

Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA.

Dr. Bofu Zheng a, Prof. Andrew J. Lucas b, Prof. Peter J.S. Franks b, Dr. Tamara L. Schlosser b, Dr. Clarissa R. Anderson b,c, Prof. Uwe Send b, Prof. Kristen Davis d, Prof. Andrew D. Barton b, Dr. Heidi M. Sosik a

Dinoflagellate vertical migration fuels an intense red tide

^{a Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
b Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
c Southern California Coastal Ocean Observing System
d Department of Earth System Sciences, University of California Irvine, Irvine, California, USA}

Harmful algal blooms (HABs) are increasing globally, causing economic, human health, and ecosystem harm. In spite of the frequent occurrence of HABs, the mechanisms responsible for their exceptionally high biomass remain imperfectly understood. A 50-y-old hypothesis posits that some dense blooms derive from dinoflagellate motility: organisms swim upward during the day to photosynthesize and downward at night to access deep nutrients. This allows dinoflagellates to outgrow their nonmotile competitors. We tested this hypothesis with in situ data from an autonomous, ocean-wave-powered vertical profiling system. In this talk, we’ll show that the dinoflagellate Lingulodinium polyedra’s vertical migration led to depletion of deep nitrate during a 2020 red tide HAB event. Downward migration began at dusk, with the maximum migration depth determined by local nitrate concentrations. Losses of nitrate at depth were balanced by proportional increases in phytoplankton chlorophyll concentrations and suspended particle load, conclusively linking vertical migration to the access and assimilation of deep nitrate in the ocean environment. Vertical migration during the red tide created anomalous biogeochemical conditions compared to 70 y of climatological data, demonstrating the capacity of these events to temporarily reshape the coastal ocean’s ecosystem and biogeochemistry. Advances in the understanding of the physiological, behavioral, and metabolic dynamics of HAB-forming organisms from cutting-edge observational techniques will improve our ability to forecast HABs and mitigate their consequences in the future.

University of Aveiro, Portugal.

Mariana S. Pandeirada a, b*, Sandra C. Craveiro a, b, Niels Daugbjerg c, Øjvind Moestrup c, António J. Calado a, b

Unveiling character evolution in peridinioid dinoflagellates: clarifying phylogeny towards a stable classification

^{a Department of Biology, University of Aveiro, P-3810-193 Aveiro, Portugal
b GeoBioTec Research Unit, University of Aveiro, P-3810-193 Aveiro, Portugal
c Marine Biological Section, Department of Biology, University of Copenhagen, Universitetsparken 4, DK-2100 Copenhagen Ø, Denmark
*mpandeirada@ua.pt}

Combination of detailed cell ultrastructure with DNA-based phylogenies has led to major changes to dinoflagellate classification over the past two decades. A series of descriptions and redefinitions of genera and families has resulted, both in athecate and thecate forms. In the thecate Peridiniales, or, in a more general sense, peridinioids, the description of new genera and the new family Peridiniopsidaceae has resulted from phylogenetic analyses using the several parts of the ribosomal operon, either concatenated or in isolation, and analyses of ultrastructural features of freshwater species previously placed in the genera Peridinium and Peridiniopsis. Our current understanding of the family Peridiniopsidaceae highlighted the unreliability of features associated with plate arrangements of the theca, even those traditionally viewed as secure markers of close relatedness between species, such as the presence or absence of an apical pore complex (apc), or the number of intercalary plates on the epicone. The family name is based on the generic name Peridiniopsis, which traditionally included species with an apc and 0-1 intercalary plates. Also included in the family are the genera Palatinus and Parvodinium, both with species common in fresh water, and later also the marine Johsia and, most recently, Chiharadinium. The group thus circumscribed now exhibits a surprising array of combinations of these features: apc absent and two intercalary plates (Palatinus); apc present and two intercalary plates (the group of species originally included in Parvodinium sensu stricto and Johsia); and apc present and three intercalary plates (Chiharadinium). In addition, Parvodinium has been shown to include also species with zero or one intercalary plates only.
In view of the inadequacy of traditional tabulation markers, we have looked at the cell organization at the ultrastructural level to try to make sense of the morphological basis of the affinity revealed by DNA sequences of members of the Peridiniopsidaceae.

C/O East China Sea Research Center, Nagasaki University, Japan.

Kazumi Matsuoka*

A reconstruction of environmental changes before and after the Anthropocene boundary (1950s-1960s) - the case of the inner part of Beppu Bay over the past 150 years using aquatic palynomorphs

*C/O East China Sea Research Center, Nagasaki University

A wide variety of organic microfossils are preserved in marine sediments. These include pollen grains, fern spores, fungal spores, dinoflagellate cysts, foraminiferal linings, ciliate remains, dormant crustacean eggs, turbellarian egg capsules, and acritarchs. These organic microfossils, except for pollen grains, fern and fungal spores, are called aquatic palynomorphs. For the reconstruction of past marine environments, observations and counting of these palynomorphs have been employed for long time. In my talk, I would like to clarify the environmental changes before and after the Anthropocene boundary in the inner part of Beppu Bay, Kyushu, Japan.

Stratigraphic cluster analysis using aquatic palynomorphs preserved in the core sediments revealed a rapid eutrophication due to anthropogenic activities from the mid 1960s in Beppu Bay. The aquatic palynomorph assemblages were divided into three major units: BP-I, BP-II and BP-III, whilst dinoflagellate cyst assemblages were divided into four different units in Beppu Bay: BP-A, BP-B, BP-C, and BP-D. Unit boundaries based on aquatic palynomorphs and dinoflagellate cysts were different except for the upper part, BP-III and BP-D, both of which clearly indicated anthropogenic eutrophication in both seawater and bottom sediments. On the other hand, in dinoflagellate cyst assemblages, Unit BP-A was characterized by a stable occurrence of the gonyaulacoid Spiniferites bulloideus and Spiniferites hyperacanthus, Lingulodinium machaerophorum, and a reduction of the heterotrophic peridinioid Brigantedinium spp. In unit BP-C, there was a clear decrease of L. machaerophorum. Unit BP-B was characterized by decreases of S. bulloideus, S. hyperacanthus, and L. machaerophorum, and a small increase of Spiniferites bentorii. Unit BP-C was characterized by an increase in S. bulloideus and the heterotrophic peridinioid Echinidinium spp. Unit BP-D was subdivided into Subunit BP-D1 where dinoflagellate cysts showed a marked increase in S. bulloideus accompanied by the appearance of L. machaerophorum and Tuberculodinium vancampoae, and Subunit PB-D2 where there was a decrease of the total of dinoflagellate cysts. From the dinoflagellate cyst assemblages, the marine environment of the period of unit BP-A was suggested to be warm and stable. However, L. machaerophorum started to decrease in BP-B. The clear decrease of L. machaerophorum suggests that the marine environment became cooler than that of Unit BP-A. Significant increases of S. bulloideus, S. hyperacanthus, L. machaerophorum, T. vancampoae, Brigantedinium spp., and Polykrikos kofoidii were characteristic of Unit BP-D. The increase in total dinoflagellate cyst density and the increase of the ratio of heterotrophic dinoflagellate cysts in Subunit BP-D1 are manifestations of the Oslo fjord Signal and heterotroph Signal, respectively. In addition, the decrease in microforaminiferal linings that continued from Unit BP-C to Unit BP-D might indicate a deterioration of the bottom sedimentary environment.

Department of Biology and Center for Environmental and Marine Studies, University of Aveiro, Portugal.

Jörg C. Frommlet*

Evidence for an autoendolithic life history of free-living symbiodiniaceans

_{*Department of Biology and Center for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal}

Dinoflagellates from the family Symbiodiniaceae engage in trophic endosymbioses with corals and various other marine hosts and play a pivotal role in sustaining the productivity and diversity of coral reef ecosystems. Yet, parallel to evolving symbiotic life histories, many symbiodiniaceans also preserved the ability to live as free-living cells outside of their hosts. The existence of these free-living populations and their importance as environmental pool from which hosts can acquire symbionts has been known for decades. Benthic habitats, especially reef sands, appear to be hotspots for free-living symbiodiniaceans, but their benthic life history has remained elusive.
A surprising new lead in the study of benthic symbiodiniaceans emerged when we discovered that in culture these dinoflagellates commonly form calcifying bacterial-algal biofilms that precipitate sand grain-like deposits and encase symbiodiniaceans as viable endolithic cells. The formation of these microbialites, we termed symbiolites, is induced by photosynthesis within the biofilm microenvironment, qualifying symbiodiniaceans as autoendoliths, i.e., organisms that actively construct their endolithic habitat through mineral precipitation. Endolithic symbiodiniaceans remain alive and photosynthetically active for weeks and upon a re-supply of nutrients they can partially dissolve the mineral and vacate the symbiolite. Because of this reversibility of the autoendolithic process, symbiolite formation does not appear to be a dead end for endolithic cells but instead points toward a transient autoendolithic phase in the life history of benthic symbiodiniaceans. Direct support for this hypothesis since emerged in form of diverse endolithic symbiodiniacean communities that we discovered across the globe.
In this seminar, I will give an overview of our work on this novel bacterial-algal calcification process, starting with its discovery in culture; over mechanistic and functional studies of the calcification process; to our latest field-based data. Further, I will discuss the potential function of creating an endolithic life stage; how endolithic populations could play an important role in the uptake of symbionts by corals; and what fate this life stage could have in the face of ocean acidification.

Biomineralization and Crystallography, Institute for Geosciences, JGU Mainz, Germany.

Anne Jantschke*, Iddo Pinkas⁺, Andreas Schertel⁺, Prof. Lia Addadi⁺ and Prof. Steve Weiner⁺

Biomineralization pathways in calcifying dinoflagellates: uptake, storage in MgCaP rich bodies and formation of the shell

_{*Biomineralization and Crystallography, Institute for Geosciences, JGU Mainz, Germany
+Structural Biology, Weizmann Institute of Science, Rehovot, Israel}

During the last decades, significant progress has been made in understanding biomineral formation in model microalgae like diatoms and coccolithophores. In contrast, the mechanisms that control the intricate mineral construction in calcareous dinoflagellates are practically unknown. Our main objectives are to gain insight into their mineral architecture, subcellular structures that may play a role in biomineralization, and calcite morphogenesis. Two representative members of calcareous dinoflagellates were investigated using cryo-electron microscopy (cryo SEM and cryo FIB SEM) in combination with various spectroscopic techniques (FT-IR, Raman, Fluorescence, EDS) enabling an investigation of cells as close as possible to the natural state.
Calcite formation occurs via multiple independent nucleation events inside the so-called outer matrix. Based on 2D and 3D cryo-electron microscopic datasets it is shown that individual calcite crystals grow with preferred orientation into a dense reticular network resulting in a highly regular, porous calcite shell.
In both species, vacuoles containing crystalline inclusions were observed using cryo-SEM. So far, crystalline deposits were assigned to calcite assuming that they are involved in shell formation. Surprisingly, using in situ Raman spectroscopic imaging these crystalline inclusions could be identified as anhydrous guanine in the biogenic β-form using their low-wavenumber Raman signature.
Interestingly, live-cell fluorescence imaging with Calcein-AM, cryo-sectioning and cryo-EDS show the presence of small MgCaP-rich mineral bodies within the same vacuolar enclosures. 3D cryo-FIB-SEM imaging of a calcifying cell shows a remarkably large number (353) of these bodies distributed in the cell volume. Out of these bodies, 52 (~15%) are located between the two inner organic layers of the outer matrix. We suggest that these MgCaP-rich bodies are being secreted into the outer matrix and are part of a Ca-concentrating or transport mechanism.
Based on our results a new dinoflagellate biomineralization model was developed which includes the active uptake of Ca2+, temporary deposition in MgCaP-precursor bodies, extrusion into the outer matrix and transformation into low Mg-calcite.

University of Oslo, Norway.

Dale, Barrie¹

Paleontological Evidence for Dinoflagellates and Ciliates as Early Eukaryotes

_{1University of Oslo, Norway.}

Molecular trees and geochemical markers suggest the divergence of dinoflagellates as early eukaryotes (~650 million years ago), but the traditional fossil record of cysts (dinocysts) starts during the Triassic (~230 million years ago). A re-evaluation of the pre-Triassic record shows that many acritarchs (microfossils of uncertain affinities) are dinocysts representing “missing” fossil evidence. Traditional diagnostic criteria for dinocysts, based on morphologic comparisons with motile stages, are biased towards thecate species. The approach proposed here, based on the more natural comparison with living cysts, includes athecate species. Many living cysts of athecate species would be “acritarchs” if found as fossils, and many earlier acritarchs would be accepted as dinoflagellate cysts if found living. The earliest acritarchs represent an innovation with profound implications for evolution: a cell wall of sporopollenin-like material enabling survival from microbial attack, in a then microbial-dominated world. Related cell wall material most likely evolved as protection for crucial
stages in sexual reproduction (e.g., cysts in ciliates and dinoflagellates, and spores and pollen in algae and plants). Ciliates and dinoflagellates may have evolved in response to extreme climatic conditions in the Cryogenian, where a robust resting cyst would be advantageous. Thecate dinoflagellates most likely evolved from athecate forms, possibly in response to predatory pressure.

Centro de Investigación Mariña (CIM), Universidade de Vigo, Departamento de Bioloxía Vexetal e
Ciencias do Solo, Facultade de Ciencias, Vigo, Spain.

García-Moreiras, I.1 , Hatherly, M.2, Zonneveld, K.3, Dubert, J.4, Nolasco, R.4, Santos, A.I.5,6, Oliveira, A. 6, Moita, T.7, Oliveira, P.B.8, Magalhães, J.9, Amorim, A.2

Physical and biological processes influencing dinoflagellate cyst distribution in the benthic nepheloid layer off Figueira da Foz (Atlantic Iberian margin)

^{1Centro de Investigación Mariña (CIM), Universidade de Vigo, Departamento de Bioloxía Vexetal e Ciencias do Solo, Facultade de Ciencias, Vigo, Spain
2Centro de Ciências do Mar e do Ambiente (MARE) /ARNET - Aquatic Research Network, , Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
3Center for Marine Environmental Sciences (MARUM) and Geosciences Department, University of Bremen, Bremen, Germany
4Centro de Estudos Do Ambiente e Do Mar (CESAM) e Departamento de Física, Universidade de Aveiro, 3810-193, Aveiro, Portugal.
5Marine Geology Division, Instituto Hidrográfico (IH), Lisbon, Portugal
6Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
7Centro de Ciências do Mar (CCMAR), Universidade do Algarve, Faro, Portugal
8Instituto Português do Mar e da Atmosfera (IPMA), Algés, Portugal
9Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR) e Departamento de Geociências, Ambiente e Ordenamento do Território (DGAOT), Universidade do Porto, Porto, Portugal}

The production of benthic resting stages (cysts) in the life cycle of many dinoflagellates is recognized as a key survival and dispersal strategy. Nevertheless, the coupling of biological and physical mechanisms involved in their transport, sedimentation and the initiation of planktonic blooms are still little understood. Where are the cysts produced before they accumulate on the sea bottom? Does the Benthic Nepheloid Layer (BNL) influence cyst distribution? Are there viable cysts in the BNL that may have the potential to seed planktonic populations? Are cysts in the BNL reflecting cyst assemblages in the underlying bottom sediments? These are some of the questions that have motivated the design of this multi-disciplinary study, which included the analysis of dinoflagellate cysts (composition and abundances) in the BNL along a land-sea transect off Figueira da Foz, NW Portuguese coast (Atlantic Iberian margin). This region is affected by seasonal upwelling that brings nutrient-rich waters and contributes to the high primary productivity that characterizes these coastal ecosystems. Environmental data and water samples were collected at different depths and in two different days (14th and 19th September 2019) to study spatial and temporal changes of physical properties and cyst assemblages. BNL cyst records were compared to planktonic records (cysts and vegetative cells from cyst-forming species) collected at different levels (0-75 m) above the BNL, along the same transect. They were also compared to the cyst rain collected by a sediment trap and with sediment cyst records to study the origin of cysts in the BNL. The survey covered a change from active to relaxed upwelling conditions with an increase of thermal stratification. In this talk I will discuss the relevance of cross- and along-shore transport on the distribution of cysts in the studied coastal transect, based on physical and biological (cysts and vegetative cells) in-situ data, along with new results obtained from particle back-track Lagrangian experiments that enabled reconstructing the trajectory of cysts in the BNL. Multi-disciplinary evidence support that during the survey the cyst distribution in the water column and underlying sediments was influenced by lateral transport in the BNL. This highlights the importance of physical transport processes on the geographical segregation of cyst production and cyst deposition areas. In consequence, cysts accumulated in the sediments are a mixture of locally and regionally produced cysts. Furthermore, high abundances of viable cysts were recorded in the BNL. Evidence suggests that during the survey, the majority of these cysts were produced in the upper water column (local or regional) rather than being resuspended from surface sediments. Cysts in BNL are exposed to higher oxygen concentrations, do not have to escape the sediment matrix and are closer to the euphotic layer, this could lead to higher germination rate and germling survival than in the bottom sediments; therefore, the BNL may act as a reservoir of viable cysts that have the potential to seed planktonic blooms.

Department of Biomolecular Sciences
University of Urbino, Campus Enrico Mattei, Urbino, Italy.

Antonella Penna¹*

Different aspects on the dinoflagellate molecular ecology: a focus on the Mediterranean Sea

_{1 Department of Biomolecular Sciences, University of Urbino, Campus Enrico Mattei, Urbino, Italy
*antonella.penna@uniurb.it}

The huge and complex biodiversity of dinoflagellates stimulated interesting ecological and molecular studies mainly aimed at harmful species worldwide. Their toxic blooms cause serious impacts to human health, marine environment, and economic maritime activities at many coastal sites. Innovative approaches and methods not only for rapid and accurate detection and count of HAB species, but also for species-specific identification and reliable quantification of abundance are in constant demand; further, the ultimate goal includes the development of early warning and forecasting systems for HABs.
In the Mediterranean Sea, in the last decades, a number of dinoflagellate species caused toxic blooms with impacts on the ecosystem functioning and human health.
Molecular and genetic population studies proved the complexity of some species (i.e., Alexandrium or Ostreopsis genera) and allowed to gain new insights into phytoplankton assemblage structure in the Mediterranean Sea. Taxon-specific primers designed on rDNA ribosomal and saxitoxin genes allowed to develop and apply new identification and counting qPCR-based assays, which proved to be more rapid, sensitive and specific when applied in various substrates, such as the water column, sediments and aerosol.
In the recent aquaculture system investigated for the PSP toxin producing species, the sxtA1 gene qPCR assay can support the analytical methods for STX determination in seawater and shellfish especially at early warning stage of toxic blooms. Further, predictive models can play an important role in managing and forecasting HABs. Models based on Machine Learning techniques and principally those based on Random Forests are very promising both at regional and at wider scale.
Very recently, plastic and microplastic debris were investigated negatively impacting the ecological functioning of oceans. The potential risk of harmful microalgae dispersal associated with plastic pollution was illustrated as well as for chemical compounds to transfer through the trophic chain with implications for human health and marine ecosystem in the Mediterranean Sea.

Department of Earth Sciences, Brock University, St. Catharines, Canada.
Natural History, Plants and Climate Change, Royal Ontario Museum, Toronto, Canada.

Francine M.G. McCARTHY^1,2*
Donya C. STINIS-DANESH^3,4*

Why do the cysts of freshwater dinoflagellates remain underutilised in paleolimnological studies?

1 Department of Earth Sciences, Brock University, St. Catharines, Canada
2 Natural History, Plants and Climate Change, Royal Ontario Museum, Toronto, Canada
* fmccarthy@brocku.ca
3 Paleoecological Environmental Assessment and Research Laboratory (PEARL), Department of Biology, Queen’s University, Kingston, Canada
4 Department of Ecosystems and Landscape Dynamics, Institute of Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands

Although they are known from non-marine sediments at least as old as Cretaceous, the cysts of freshwater dinoflagellates are rarely employed as paleolimnological proxies, especially compared to other algal microfossil groups. There are two main reasons for this: 1) taxonomic- most palynologists fail to recognize cysts other than those with clear peridinialean morphologies as having dinoflagellate affinities, and theca-cyst relationships have been conclusively documented for a relatively small proportion of freshwater dinoflagellate taxa; and 2) taphonomic – the few attempts to relate cyst assemblages with phycological assemblages have identified a complex relationship, and the effects of taphonomy, on cyst assemblages remain relatively poorly understood. Water column-to-lakebed studies (including sediment trap analysis) and laboratory exposure of cyst assemblages to oxidation undertaken from lakes in the Dorset Lakes region of south-central Ontario has shed light on these issues, in particular illustrating the effects of differential susceptibility to oxidation on cyst assemblages. While taxonomic and taphonomic issues exist in marine environments, substantial effort has been expended to relate the distribution of dinoflagellate cysts in modern marine sediments with environmental parameters, allowing development of transfer functions. In contrast, the first calibration set was recently created, identifying lake depth, trophic state and pH as the most important environmental variables controlling the distribution of 38 cyst morphotypes in 32 lakes in the Experimental Lakes Area of northwestern Ontario, Canada. Applying lessons learned from these investigations to a core from which several other paleoenvironmental proxies have been studied illustrates the current value of dinoflagellate cysts in paleolimnological investigations and suggests where additional effort should be focused to maximize their potential.

Department of Freshwater and Marine Ecology (FAME), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam.

Corina Brussaard^1*

Phytoplankton virus ecology (with a focus on Phaeocystis)

<sup>1a Department of Freshwater and Marine Ecology (FAME), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, P.O. Box 94920, 1090
XH, Amsterdam, The Netherlands
2 Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands
* Corina.Brussaard@nioz.nl</sup>

With more than 70% of the living biomass in the oceans being microbial, marine viruses have plenty of unicellular hosts to choose from. Viruses for all taxonomic phytoplankton groups have been reported but a more detailed comprehension of their impact on population dynamics of the various phytoplankton under natural conditions is still limited. Using methods developed to enumerate aquatic viruses and determine the host specific mortality rates in the field, we show that viral lysis is a highly important loss factor for marine phytoplankton with average rates comparable to the more traditional losses by grazing. We translate our findings to carbon to better understand how viral activity affects the transfer of matter & energy, as well as the biogeochemical cycling. Dependent on their hosts’ metabolism, viral production is influenced by environmental factors affecting host growth and viability. At the same time, environmental variables regulate viral abundance through particle decay and loss of infectivity. Considering the increasing pressure of global climate change on aquatic systems, it is timely to study also virus-host interactions under different environmental conditions. Well-controlled experimental studies using key virus-host model systems are used to unravel underlying mechanisms. During this presentation, I will focus on the harmful algal species Phaeocystis globosa and highlight the level of viral control on population dynamics, the influence of key environmental factors.

CSS, Inc. Under Contract to National Oceanic and Atmospheric Administration (NOAA), National Ocean Service, National Centers for Coastal Ocean Science, Beaufort, North Carolina, USA.

R. Wayne Litaker¹ and Brittany Ott^2*

Criteria for using rDNA sequences to define dinoflagellate species

<sup>1 CSS, Inc. Under Contract to National Oceanic and Atmospheric Administration (NOAA), National Ocean Service, National Centers for Coastal Ocean Science, Beaufort Laboratory, Beaufort, North Carolina, United States of America. Wayne.R.Litaker@noaa.gov
2 Joint Institute for Food Safety and Applied Nutrition (JIFSAN), University of Maryland—College Park, College Park, MD, United States of America, Cell Biology and Molecular Genetics, University of Maryland—College Park, College Park, MD, United States of America
* Currently at: Center for Food Safety and Applied Nutrition, Office of Food Additive Safety, Department of Science and Technology—College Park, College Park, MD, United States of America.
brittany.ott@fda.hhs.gov</sup>

rDNA sequences have been used to successfully delineate species in numerous animal and plant lineages. For dinoflagellates, the degree to which rDNA-based phylogenies can be used to distinguish species is controversial with some researchers arguing single gene phylogenies are inadequate and that only multigene phylogenies can provide sufficiently strong molecular evidence for species boundaries. This study was consequently undertaken to (1) begin addressing the efficacy of rDNA versus multigene phylogenies to delineate dinoflagellate species, (2) to conduct an extensive literature survey encompassing 473 manuscripts representing 232 genera and 863 described species to quantify how well SSU, ITS/5.8S or 5’ LSU phylogenies successfully delineated morphologically defined dinoflagellate species, and (3) to determine if a defined scheme governing how to jointly weight morphological characters versus rDNA phylogenies when describing dinoflagellate species could be developed. To address these questions, we constructed transcriptomic libraries for nine Gambierdiscus species and downloaded previously published libraries for related species to determine how well the D1-D3 and ITS/5.8S rDNA gene regions versus multigene phylogenies delineate these species. Both the D1-D3 and ITS/5.8S phylogenies and the multigene phylogenies were found to identify Gambierdiscus and Alexandrium species equally well. Results from the literature survey showed joint D1-D3 rDNA and ITS phylogenies are capable of identifying 97% of described dinoflagellate species, including all the species currently belonging to the harmful algal bloom genera Alexandrium, Ostreopsis and Gambierdiscus. The results from objectives 1 and 2 were sufficient to construct a protocol for identifying when ITS/5.8S rDNA sequence data would take precedence over morphological features in describing new dinoflagellate species. The protocol addresses situations such as: a) when a new species is both morphologically and molecularly distinct from other known species; b) when a new species and closely related species are morphologically indistinguishable, but genetically distinct; and c) how to handle potentially cryptic species and cases where morphotypes are clearly distinct but have the same rDNA sequence. The protocol also addresses other molecular, morphological, and genetic approaches required to resolve species boundaries in the small minority of species where the D1-D3/ITS region phylogenies fail.

Department of Biological Sciences, Hokkaido University, Japan.

Kevin C. WAKEMAN^1*

Patterns of Evolution and Diversity of Symbiotic Marine Alveolates

<sup>1 Institute for the Advancement of Higher Education, Hokkaido University, Japan
* wakeman.kevin@gmail.com</sup>

Alveolates are a diverse group of single celled eukaryotes (protists) that have been traditionally defined by three major groups: apicomplexans, dinoflagellates, and ciliates. More contemporary work on select alveolate lineages (i.e., early diverging parasitic lineages) has let researchers in this field revisit some of the earliest stages of alveolate evolution. In this talk, I will give a brief introduction to alveolate lineages, covering some of the recent advances in the field. In particular, I will discuss on-going themes related to the early diversification and host specificity of parasitic alveolates within the genera Haplozoon, and Platyproteum. Here, I will present some preliminary work that highlights coevolutionary patterns (host specificity) between these parasites and their hosts. I will also cover some of the character evolution of these groups that make them intriguing models for understanding the early evolution of alveolates and the independent evolutionary transition from a free-living (photosynthetic) ancestor to an obligate parasitic niche.

Department of Oceanography, Texas A&M University, College Station, Texas, USA.

James M. FIORENDINO¹, Daniel L. ROELKE², Lisa CAMPBELL¹

Portion Control: Modelling the Effect of Prey Size on Dinophysis Blooms in the Gulf of Mexico

^{1Department of Oceanography, Texas A&M University, College Station, TX 77843, USA
2Department of Marine Biology, Texas A&M University at Galveston, Galveston, TX, 77553, USA
*fiorenja@tamu.edu}

Increasingly common blooms of toxic Dinophysis species represent a threat to human health and shellfish fisheries in the United States. The dependence of mixotrophic kleptoplastidic Dinophysis species on specific prey, the marine ciliate Mesodinium rubrum, further complicates predicting and mitigating the impacts of Dinophysis blooms. A decade of high temporal resolution monitoring of the phytoplankton community along the Texas, United States coast with Imaging FlowCytobots (IFCB) has revealed seasonal Dinophysis ovum blooms of varying intensity that occur between January and April in the Gulf of Mexico. Previous analysis of IFCB field data revealed a weak time-lagged relationship between D. ovum and Mesodinium abundance. Recent laboratory culturing experiments have indicated temperature and prey biomass are important factors influencing Dinophysis biomass and growth rates. Utilizing data from laboratory culturing experiments and the Texas Observatory for Algal Succession Timeseries, we developed a model of Dinophysis and prey population dynamics in the Gulf of Mexico. The model results indicated prey biomass, rather than abundance alone, was a more reliable predictor of D. ovum bloom onset and intensity. We also found temperature played an important role in the onset of D. ovum blooms, specifically overlap of D. ovum and its prey. The influence of future warming on D. ovum bloom dynamics in the Gulf of Mexico will determine whether increases in D. ovum bloom frequency or intensity are likely to occur.

Department of Physics, Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University. Centre for Complex Systems Studies, Utrecht University, Utrecht, the Netherlands.

Peter D. NOOTEBOOM^1,2*

The journey of sinking marine microplankton and its implication for palaeoceanographic reconstructions

<sup>1 Department of Physics, Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Utrecht, Netherlands
2 Centre for Complex Systems Studies, Utrecht University, Utrecht, Netherlands
* p.d.nooteboom@uu.com</sup>

A primary part of the Earth's archive to reconstruct past climates is provided by marine sediments, consisting of (fossil remains from) microplankton. The microplankton species in the bottom sediments originated from a location close to the ocean surface before they started sinking to the bottom. Hence, microplankton at the ocean bottom is representative of the ocean surface environment and can be used for palaeoceanographic reconstructions. It is often assumed that these planktonic species sunk vertically downwards. However, the microplankton is transported laterally by ocean currents during its sinking journey.
Here we model the transport of dinoflagellate cysts (dinocysts) during their sinking journey in global high-resolution (0.1˚ horizontally) model simulations of the present-day and middle-late Eocene oceans. We investigate the implications of their lateral displacement on the interpretation of sedimentary dinocyst data when these are used for palaeoceanographic reconstructions.
For example, if subtropical microplankton species are found near Antarctica in a specific time period, two hypotheses can be tested with this method: (a) the ocean near Antarctica had subtropical temperatures, or (b) Antarctica was not subtropical, but the microplankton were transported laterally by ocean currents and originated from another region with subtropical temperatures.

Ifremer, PHYTOX, Laboratoire METALG, Nantes, France.

PHILIPP HESS^1*, KENNETH MERTENS², NICOLAS CHOMERAT², VERONIQUE SECHET³, FABIENNE HERVE¹, LOÏC PLESSIS¹, DAMIEN REVEILLON¹, PATRICE BREHMER⁴

Vulcanodinium rugosum - a potent and ubiquitous genus affecting mice and man

<sup>1 Ifremer, PHYTOX, Laboratoire METALG, 44000 Nantes, France
2 Ifremer, LITTORAL, LER-BO, 29000 Concarneau, France
3Ifremer, PHYTOX, Laboratoire PHYSALG, 4400, France
4 IRD, Univ Brest, CNRS, Ifremer, Lemar, Sub Regional Fisheries Commission (SRFC), Dakar, Senegal
* philipp.hess@ifremer.fr</sup>

The monotypic genus Vulcanodinium was erected in 2011 [1], and the unique species V. rugosum was associated with the production of pinnatoxins the same year [2]. According to its morphology, V. rugosum is closely related to peridinioid/scrippsielloid dinoflagellates, such as the genus Bysmatrum from which it can be distinguished mainly by the pattern of anterior intercalary plates. Based on LSU rDNA sequence data, the taxon was shown to belong to the order Peridiniales but it was not possible to affiliate it to a particular family, and molecular data showing a rather high divergence from other peridinioids supports the erection of the genus. Few studies focused on the life cycle of this organism [3, 4], but while V. rugosum has been observed as a pelagic species, it also frequently forms clusters of non-motile (temporary cyst-like) cells embedded in a highly adherent mucous. Its pelagic life forms obviously may contribute to its spread and some of the effects discussed below.
Pinnatoxins (PnTXs), and their derivatives, pteriatoxins (PtTXs), are a group of macrocycles with cyclic imine and spiro-functions similar to spirolides and have been identified in shellfish well before the discovery of their causative organism [5-9]. Pinnatoxins are potent neurotoxins that were discovered using an isolation scheme bioguided by intraperitoneal mouse bioassay [7]. The toxins act via blocking neurotransmission through their strong binding to the nicotinic acetylcholine receptor [10, 11], and also activate Ca2+-channels and inhibit expression of vascular cell adhesion molecule 1 (VCAM-1) [12]. After isolation of a peridinioid dinoflagellate producer in New Zealand and the isolation of pinnatoxins E and F in 2010 [13, 14], pinnatoxins were also rapidly reported in Australia, China, Japan, Canada and Europe in both algal strains and shellfish in areas of different ecology, notably Norway and France [2, 4, 15-20], even if numerous ecological studies suggest warm water temperatures as a driver for significant bloom development [21-24]. There is significant diversity of PnTXs among strains isolated from different regions which may vouch for further studies on intra-specific genetic diversity, and ballast water or other ship vectors have been suggested as a possible route of distribution of these organisms around the globe.
Studies on the cytotoxicity of the first French strain suggested presence of several toxins [25, 26]. Indeed, a novel toxin, i.e. portimine, was simultaneously reported from a New Zealand strain. Portimine is a small macrocycle that also contains a cyclic imine group but only a single carbon with spiro-functionality, and presents greater cytotoxicity than PnTXs. Contrarily to the diversity of PnTXs, all strains characterized globally appear to produce portimine. Shellfish appear to preferentially accumulate PnTXs rather than portimine, and PnTXs have been classified as fast acting or presenting atypical toxicity observed in mice, i.e. symptoms within 15 min. Still, to date, no acute intoxication through consumption of shellfish by humans has been confirmed to have been caused by PnTXs. Surprisingly, a bloom of V. rugosum in Cienfuegos Bay, Cuba, has been reported to cause dermatitis in bathers [24], and we report here an event in Senegal where, in addition to PnTX-H, record values for portimine occurred in an offshore environment affecting artisanal fishermen with similar symptoms in 2020 and 2021. Further research is underway to elucidate causative compounds and mechanisms of toxicity as well the genetic signature of strains involved.

References

1. Nézan, E. and N. Chomérat, Vulcanodinium rugosum gen. et sp. nov. (Dinophyceae), un nouveau dinoflagellé marin de la côte méditerraneenne française. Cryptogamie, Algologie, 2011. 32(1): p. 3-18.
2. Rhodes, L., et al., Dinoflagellate Vulcanodinium rugosum identified as the causative organism of pinnatoxins in Australia, New Zealand and Japan. Phycologia, 2011. 50(6): p. 624-628.
3. Abadie, E., Etude de Vulcanodinium rugosum (Dinoflagellé producteur de pinnatoxines) se développant dans la lagune méditerranéenne de l’Ingril. 2015, Université de Montpellier.
4. Zeng, N., et al., The first report of Vulcanodinium rugosum (Dinophyceae) from the South China Sea with a focus on the life cycle. New Zealand Journal of Marine and Freshwater Research, 2012. 46(4): p. 511-521.
5. Zheng, S.Z., et al., The isolation and bioactivities of pinnatoxin. Chin. J. Mar. Drugs, 1990. 33: p. 33-35.
6. Chou, T., et al., Structure of pinnatoxins, potent shellfish poisons. Tennen Yuki Kagobutsu Toronkai Koen Yoshishu, 1994. 36th: p. 57-64.
7. Uemura, D., et al., Pinnatoxin A: a toxic amphoteric macroycle from the Okinawan bivalve Pinna muricata. J. Am. Chem. Soc., 1995. 117: p. 1155-1156.
8. Chou, T., et al., Isolation and structure of pinnatoxin D, a new shellfish poison from the okinawan bivalve Pinna muricata. Tetrahedron Letters, 1996. 37(23): p. 4027-4030.
9. Takada, N., et al., Structural determination of pteriatoxins A, B and C, extremely potent toxins from the bivalve Pteria penguin. Tetrahedron Letters, 2001. 42(20): p. 3495-3497.
10. Araoz, R., et al., Total Synthesis of Pinnatoxins A and G and Revision of the Mode of Action of Pinnatoxin A. Journal of the American Chemical Society, 2011. 133(27): p. 10499-10511.
11. Hellyer, S.D., et al., Marine algal pinnatoxins E and F cause neuromuscular block in an in vitro hemidiaphragm preparation. Toxicon, 2011. 58(8): p. 693-699.
12. Kuramoto, M., H. Arimoto, and D. Uemura, Studies in bioactive marine alkaloids. Journal of Synthetic Organic Chemistry Japan, 2003. 61(11): p. 1099-1105.
13. Rhodes, L., et al., Production of pinnatoxins by a peridinoid dinoflagellate isolated from Northland, New Zealand. Harmful Algae, 2010. 9(4): p. 384-389.
14. Selwood, A.I., et al., Isolation, Structural Determination and Acute Toxicity of Pinnatoxins E, F and G. Journal of Agricultural and Food Chemistry, 2010. 58(10): p. 6532-6542.
15. Rhodes, L., et al., Production of pinnatoxins E, F and G by scrippsielloid dinoflagellates isolated from Franklin Harbour, South Australia. New Zealand Journal of Marine and Freshwater Research, 2011. 45(4): p. 703-709.
16. Rundberget, T., et al., Pinnatoxins and spirolides in Norwegian blue mussels and seawater. Toxicon, 2011. 58(8): p. 700-11.
17. Smith, K.F., et al., A dinoflagellate producer of pinnatoxin G, isolated from sub-tropical Japanese waters. Harmful Algae, 2011. 10(6): p. 702-705.
18. Hess, P., et al., Pinnatoxines en lien avec l’espèce Vulcanodinium rugosum. 2012.
19. McCarron, P., et al., Identification of pinnatoxins and discovery of their fatty acid ester metabolites in mussels (Mytilus edulis) from Eastern Canada. Journal of Agricultural and Food Chemistry, 2012. 60(6): p. 1437-46.
20. Hess, P., et al., Pinnatoxin G is responsible for atypical toxicity in mussels (Mytilus galloprovincialis) and clams (Venerupis decussata) from Ingril, a French Mediterranean lagoon. Toxicon, 2013. 75: p. 16-26.
21. Hernandez-Becerril, D.U., M.C. Rodriguez-Palacio, and C. Lozano-Ramirez, Morphology and life stages of the potentially pinnatoxin-producing thecate dinoflagellate Vulcanodinium rugosum from the tropical Mexican Pacific. Botanica Marina, 2013. 56(5-6): p. 535-540.
22. Abadie, E., et al., Toxin and growth responses of the neurotoxic dinoflagellate Vulcanodinium rugosum to varying temperature and salinity. Toxins, 2016. 8(5): p. 18.
23. Abadie, E., et al., What are the main environmental factors driving the development of the neurotoxic dinoflagellate Vulcanodinium rugosum in a Mediterranean ecosystem (Ingril lagoon, France)? Harmful Algae, 2018. 75: p. 75-86.
24. Moreira-Gonzalez, A.R., et al., Summer bloom of Vulcanodinium rugosum in Cienfuegos Bay (Cuba) associated to dermatitis in swimmers. Science of the Total Environment, 2021. 757: p. 12.
25. Geiger, M., et al., Cytotoxicity, fractionation and dereplication of extracts of the dinoflagellate Vulcanodinium rugosum, a producer of Pinnatoxin G. Marine Drugs, 2013. 11(9): p. 3350-3371.
26. Geiger, M., et al., Cellular models and cytotoxicity of pinnatoxin-G and extracts of the dinoflagellate Vulcanodinium rugosum recently isolated from the French mediterranean lagoon of Ingril. Toxicon, 2013. 75(0): p. 215-216.

Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands.

Peter K. BIJL¹

DINOSTRAT: A global database of the stratigraphic and paleolatitudinal distribution of Mesozoic-Cenozoic organic-walled dinoflagellate cysts

<sup>1 Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands
* p.k.bijl@uu.nl</sup>

Mesozoic–Cenozoic organic-walled dinoflagellate cyst (dinocyst) biostratigraphy is a crucial tool for relative and absolute age control in complex ancient sedimentary systems. However, stratigraphic ranges of dinocysts are found to be strongly diachronous geographically. A global compilation of state-of-the-art calibrated regional stratigraphic ranges could assist in quantifying regional differences and evaluate underlying causes. For this reason, DINOSTRAT is initiated – an open source, iterative, community-fed database intended to house all regional chronostratigraphic calibrations of dinocyst events (https://github.com/bijlpeter83/DINOSTRAT.git). DINOSTRAT version 2.0 includes >8500 entries of first and last occurrences (collectively called “events”) of >1900 dinocyst taxa, and their absolute ties to the chronostratigraphic time scale of Gradstein et al., 2020. Entries are derived from over 200 publications and 190 sedimentary sections. DINOSTRAT interpolates paleolatitudes of regional dinocyst events, allowing evaluation of the paleolatitudinal variability of dinocyst event ages. DINOSTRAT allows for open accessibility and searchability, on region, age, and taxon. In my seminar, I will present a selection of the data in DINOSTRAT: (1) the (paleo)latitudinal spread and evolutionary history of modern dinocyst species; (2) the evolutionary patterns and paleolatitudinal spread of dinoflagellate cyst (sub)families; (3) a selection of key dinocyst events which are particularly synchronous. Although several dinocysts show – at the resolution of their calibration – quasi-synchronous event ages, indeed many species have remarkable diachroneity. DINOSTRAT provides the data storage approach by which the community can now start to relate diachroneity to (1) inadequate tie to chronostratigraphic time scales; (2) complications in taxonomic concepts and (3) ocean connectivity and/or the affinities of taxa to environmental conditions. I aim to convince the audience to contribute to DINOSTRAT in the future, with comments, publications and suggestions.

Earth Sciences, University College London, UK.

_{Jeremy R. YOUNG1*, Ian PROBERT2, Kenneth Neil MERTENS3, Jane M. LEWIS4}

Dinotax - first stages of establishing a web-database of extant dinoflagellate taxonomy

1 Earth Sciences, University College London, UK
2 Sorbonne Université, CNRS, FR2424 Station Biologique de Roscoff, France
3 Ifremer, LITTORAL, Place de la Croix, BP40537, 29900 Concarneau CEDEX, France
4 Shetland UHI, Shetland, UK
* jeremy.young@ucl.ac.uk

Learning, communicating and synthesising taxonomy has always been a challenge, especially in groups such as dinoflagellates with high diversity and wide biogeographic distribution. We have recently received French funding for a major research project “Phenomap” focussed on improving knowledge of phytoplankton diversity, taxonomy and phylogeny. As part of this we aim to develop a new online database of extant dinoflagellate taxonomy, building on the success of the Nannotax (www.mikrotax.org/Nannotax3) and pforams@mikrotax (www.mikrotax.org/pforams) databases, which cover coccolithophores (and other haptophytes) and planktonic foraminifera respectively. These systems have achieved the objectives of proving accessible and authoritative online syntheses and are very well-used by students, researchers and consultants across the globe, both as reference tools and as practical identification guides. The Dinotax database will have a similar structure to those systems, and, although dinoflagellates are a much more diverse group, it will be of similar size, since it will only deal with extant taxa (fossil dinocyst taxonomy is synthesised separately by DINOFLAJ, Williams et al. 2017, and their stratigraphy and paleolatitudinal distribution by DINOSTRAT, Bijl 2022). Dinotax will include both a catalogue database of all described species and a separate, but linked, database providing a monographic overview of current working taxonomy. With generous assistance from Mike Guiry the basic taxonomic framework of these two databases has been created and linked to a bibliographic database (with PDFs). We are now preparing to develop the database by collecting images and reviewing recent syntheses on dinoflagellate taxonomy.
This talk will provide a first opportunity to introduce the project to a wider group of dinoflagellate specialists, and we are very open to suggestions, discussion of priorities and, of course, offers of help.

References

• Williams, G.L., Fensome, R.A., and MacRae, R.A., 2017. DINOFLAJ3. American Association of Stratigraphic Palynologists, Data Series no. 2. http://dinoflaj.smu.ca/dinoflaj3.
• Bijl, P.K., 2022. DINOSTRAT: a global database of the stratigraphic and paleolatitudinal distribution of Mesozoic–Cenozoic organic-walled dinoflagellate cysts. Earth Syst. Sci. Data 14, 579-617.

Systematics, Biodiversity and Evolution of Plants, Ludwig-Maximilians-University Munich (LMU), Munich, Germany.

_{Juliana CHACÓN1*, Uwe JOHN2, Juliane KRETSCHMANN1, Stefan NEUHAUS2, Herwig STIBOR3, Anže ŽERDONER ČALASAN1, Marc GOTTSCHLING1}

Dinophyte diversity in Bavarian lakes and algal species successions at Munich Botanical Gardens (Germany): Using phylogenetic placement of environmental sequences and reliable taxonomic databases to study algal biodiversity

_{1 Systematics, Biodiversity and Evolution of Plants, Ludwig-Maximilians-University Munich (LMU), Munich, Germany
2 Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, AWI, Bremerhaven, Germany
3 Aquatic Ecology, Biology II, LEMAR, Ludwig-Maximilians University Munich (LMU), Munich, Germany
*Juliana.chacon@bio.lmu.de}

Reliable determination of organisms is the necessary prerequisite to explore their spatial and temporal distribution and to study their evolution, ecology and dispersal. The Bavarian state in Germany provides a great study system for research on the origin and diversification of freshwater organisms including dinophytes, due to the presence of extensive lake districts and ice age river valleys, which are ecologically very diverse. In this study, we obtained amplicon sequence data (SSU-rRNA) from environmental samples collected in Upper Bavaria. Using bioinformatic pipelines, we found 186 dinophycean operational taxonomic units (OTUs) that were further classified by means of a phylogenetic placement approach. The Maximum likelihood tree as inferred from a well-curated reference alignment comprised a systematically representative set of 241 dinophytes, covering the known molecular diversity and considering type material. Environmental OTUs were scattered over the reference tree, but accumulated mostly in freshwater lineages, especially taxa that are frequently encountered in Bavaria (i.e., Apocalathium, Ceratium or Peridinium). Particularly within Peridiniaceae, intraspecific sequence variation was suitable to determine species of Peridinium. Twenty-one OTUs showed identical sequences to known and vouchered sequences, of which two have been gained from type material, namely Palatinus apiculatus and Theleodinium calcisporum. Our approach indicates that high-throughput sequencing of environmental samples is effective for reliable determination of freshwater dinophytes and highlights the importance of well-curated reference data bases. We are now using this methodology within a biomonitoring project, which is being conducted at the ponds of the Munich Botanical Gardens. Our metabarcoding approach aims to examine the algal diversity in terms of seasonality and annual species successions. The goal is to develop awareness of the importance of the microalgal biodiversity in this microbial domain and their impact in the context of the current climate change.

Institut de Ciències del Mar (CSIC) Barcelona, Spain.

_{Albert REÑÉ1*}

Insights on sand-dwelling dinoflagellates communities combining morphological and metabarcoding approaches

<sub>1 Institut de Ciències del Mar (CSIC) Pg. Marítim de la Barceloneta, 37-49 08003 Barcelona, Catalonia (Spain)
* albertrene@icm.csic.es</sub>

Around 10% of known marine dinoflagellates species are benthic. However, the diversity of sand-dwelling dinoflagellates remains unexplored in many areas, and little is known about their distribution and ecology. During last years, efforts have been conducted to determine the community composition of sand-dwelling dinoflagellates in the NW Mediterranean Sea combining morphological (light and electron microscopy) and molecular (single-cell PCR, metabarcoding of V4 18S rDNA) techniques. Such approach was also performed in the German Wadden Sea, an area were benthic dinoflagellates are well known. The morphological characterization and molecular information obtained resulted in the description of several new species and genera, and the taxonomic reclassification of some others. The performance of treatments commonly used to retrieve genomic DNA from sediments was then evaluated, determining the accuracy of information obtained by metabarcoding. The molecular characterization of Mediterranean communities allowed the observation of some trends in the temporal dynamics during spring and summer, including the temporality of some species. Additionally, significant differences in the community composition of Wadden Sea locations were observed. All these studies highlight that a better performance is achieved when combining microscopy observations and molecular approaches. In any case, efforts are still needed to characterize sand-dwelling dinoflagellates, and to better understand the spatial and temporal distribution of species and their ecological role.

Department of Geology, Ghent University, Ghent, Belgium.

_{Pieter R. GURDEBEKE1*, Kenneth N. MERTENS2, Vera POSPELOVA3,4, Kazumi MATSUOKA5, Zhen LI4, Kristin E. GRIBBLE6, Haifeng GU6, Kara BOGUS8,9, Henk VRIELINCK10, Stephen LOUWYE1}

The dinoflagellate cyst genus Votadinium Reid (Dinophyceae, Peridiniales, Protoperidiniaceae): Taxonomic revision, phylogeny, and cyst wall composition

<sub>1 Department of Geology, Ghent University, Ghent, Belgium.
2 Ifremer, LITTORAL, Concarneau, France
3 Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA
4 School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada.
5 Institute for East China Sea Research (ECSER), Taira-machi, Nagasaki, Japan
6 Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, USA.
7 Third Institute of Oceanography, State Oceanic Administration, Xiamen, China
8 International Ocean Discovery Program, Texas A&M University, College Station, TX, USA.
9 Camborne School of Mines, University of Exeter, Penryn, Cornwall, UK.
10 Department of Solid State Sciences, Ghent University, Ghent, Belgium
* pieter.gurdebeke@ugent.be</sub>

The taxonomy of the dinoflagellate cyst-based genus Votadinium has been in need of revision. This is accomplished here by integrating morphology, large subunit (LSU) rDNA sequences, and cyst wall composition analyses through micro-Fourier transform infrared spectroscopy. Three new species, Votadinium pontifossatum, V. rhomboideum and V. reidii, are described as cyst stages of Protoperidinium paraoblongum, P. quadrioblongum, and P. steidingerae, respectively. A previously undescribed type of ornamentation is reported for V. pontifossatum. A fourth new species is assigned to V. concavum. Furthermore, Lejeunecysta psilodora Benedek (= Lejeunecysta psuchra Matsuoka), is re-described as V. psilodora and the holotype re-illustrated, as is done for the holotype of V. spinosum Reid. New illustrations are provided for V. elongatum and V. nanhaiense. LSU rDNA sequences of V. concavum reveal its placement in the Oceanica section of the genus Protoperidinium, supporting earlier evidence that the Oceanica section and the cyst-based genus Votadinium form a monophyletic clade. Thus, Votadinium could be considered the cyst equivalent of the motile-defined Oceanica section. The cyst walls of Votadinium spinosum, V. calvum and V. pontifossatum are built from carbohydrate-based macromolecules with N-containing functional groups, in agreement with the heterotrophic nature of their motile stage. Comparison with related genera Trinovantedinium and Quinquecuspis reveals that the species and genera can be separated based on cyst wall composition, supporting a phylogeny based on molecular data and/or ecological differences. Furthermore, Trinovantedinium applanatum spectra unexpectedly show an additional absorption at 1510 cm−1, indicating an aromatic group that is commonly reported for sporopollenin and not seen in dinoflagellate cysts so far. This study stabilizes the taxonomy of the cyst genus Votadinium, clarifies its relationship to the Oceanica section of Protoperidinium, and further supports the application of whole cyst wall chemistry in helping address problems in dinoflagellate cyst taxonomy and ecology.

Department of Ocean Science, Faculty of Marine Environment and Resources, Tokyo University of Marine Science and Technology, Tokyo, Japan.

_{Leila BASTI1*, Satoshi NAGAI2, Kyohito NAGAI3}

Food Security and Harmful Dinophyte Blooms: Impacts on Aquaculture and Recent Advances in Biosensors and Molecular Detection

<sub>1 Department of Ocean Science, Faculty of Marine Environment and Resources, Tokyo University of Marine Science and Technology, Tokyo, Japan
2 Japan Fisheries Research and Education Agency, National Research Institute of Fisheries Science, Yokohama, Japan
3 Pearl Research Laboratory, K. Mikimoto & Co. LtD., Mie, Japan
* bastileila@gmail.com</sub>

Aquaculture is expected to expand globally in response to a surge in the demand for a new source of protein as conventional agriculture systems are declining, especially in regions seeing a significant growth of their human populations. Marine and freshwater aquaculture is seen as the most environmentally-friendly food production system that would offer a sustainable alternative to the traditional plant and livestock categories. Numerous natural and engineered environments are seen as suitable for an unlimited opportunity for food production and growth over the coming decades.
However, several constraints including harmful algal blooms (HAB) will hamper the provision of long-term food security. HAB have been increasing globally over the past decades due to many factors, including climate change and increased anthropogenic pressures on freshwater and coastal environments paralleled to increased aquaculture activities. With the recent alarming projections of significant climatic and oceanic shifts driven by climate change, constraints to aquaculture systems need to be addressed in a more urgent way to secure the future of food production. In particular, dinophytes represent the most widespread HAB that have been forming recurrent blooms of devastating impacts on aquaculture farms. In the present seminar, a historical overview of the impacts of harmful dinophytes on aquaculture farms driven from global data is given, as well as the toxic effects of the most recurrent harmful dinophytes on fish and shellfish from experimental studies. The recent advances in the developments of biosensors and molecular detection tools for prediction and biomonitoring of harmful dinophytes are also presented.

Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands.

_{Lena M. THÖLE1*, Peter D. NOTEBOOM2,3 Suning HOU1, Ruijan WANG4, Senyan NIE4, Elisabeth MICHEL5, Isabel SAUERMILCH1, Fabienne MARRET6, Francesca SANGIORGI1, Peter K. BIJL1}

Closing the Antarctic Void: Tighter Constraints on Biogeographic Affinities of Modern Dinoflagellate Cyst Assemblages in the Southern Ocean with Implications for Sea Surface Temperatures and Sea Ice Reconstructions

<sub>1 Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands
2 Institute for Marine and Atmospheric Research Utrecht, Utrecht, the Netherlands
3 Centre for Complex System Studies, Utrecht University, Utrecht, the Netherlands
4 State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
5 Laboratoire des Sciences du Climate et de l’Environnement, LSCE/IPSL, University de Paris-Saclay, Gif-sur-Yvette, France
6 Department of Geography and Planning, University of Liverpool, Liverpool, United Kingdom
* l.m.thole@uu.nl</sub>

Dinoflagellate cyst assemblages are used to reconstruct paleosurface ocean conditions such as sea surface temperature (SST), nutrients or sea ice for Antarctic Circumpolar Current-specific zones and fronts. Yet, a low surface sediment sample coverage in ice-proximal sites increases the uncertainty in polar environments and limits the use of dinocyst assemblages as sea ice proxy.
Here, we present a new dataset (n = 73) of surface sediment dinoflagellate cyst assemblages from ice-proximal locations around Antarctica. We add this to previously published data for the Southern Hemisphere (now 655 samples) to capture the distribution along the full range of environmental gradients. We perform k-means clustering on an ice-proximal and the entire southern hemisphere data set to potentially distinguish regional ice-proximal and southern hemispheric latitudinal differences. We reproduce a similar clustering as found previously, with additional clusters in the AZ dominated by Selenopemphix antarctica or Islandinium minutum.
A part of the uncertainty in dinocyst-environment relationships has been ascribed to strong lateral particle transport in the Southern Ocean. To incorporate this potential influence, we compare environmental parameters of overlying surface waters for each cluster with those derived from Lagrangian particle tracking simulations in a high-resolution (1/12° horizontally) ocean model with 25 m/day sinking speed. In general, we find similarly constrained cluster-specific environmental parameters when lateral transport is considered.
Our results emphasize the potential of dinoflagellate cysts as valuable proxies for SST and sea ice in the Southern Hemisphere. Considering lateral particle transport better represents the source regions but does not change the assigned environmental parameters. This encourages future efforts to translate dinocyst assemblages into quantitative tools for paleoceanographic reconstructions.

Estuary Research Center, Shimane University, Matsue, Japan.

_{Takuto ANDO1*, Kazumi MATUOKA2, Karin ZONNEVELD3, Gerard VERSTEEGH4, Mika ISHIGAKI5, Tatsuyuki YAMAMOTO6}

Macromolecules analyses of cyst wall of Alexandrium catenella/pacificum using ATR-FTIR and Raman spectroscopy

<sub>1 Estuary Research Center, Shimane University, Matsue, Japan
2 Institute for East China Sea Research, Nagasaki University, Nagasaki, Japan
3 Center for Marine Environmental Sciences (MARUM), Bremen University, Bremen, Germany
4 Marine Biochemistry Section, Alfred-Wegener-Institute, Bremerhaven, Germany
5 Center for Promotion of Project Research. Shimane University, Matsue, Japan
6 Faculty of Life and Environmental Sciences, Shimane University, Matsue, Japan
* tact@soc.shimane-u.ac.jp</sub>

Blooms (red-tides) caused by dinoflagellates, especially toxic/harmful species, in coastal waters adversely impact both marine ecosystems and human health. Formation of dinocysts and their preservation in the sediments are therefore essential subjects for understanding the bloom mechanisms. Alexandrium catenella/pacificum are toxic species (paralytic shellfish poisoning) that produce elliptical transparent cysts. These cysts are generally rather labile than those of other gonyaulacoid cysts. The lability of dinocysts during early diagenesis is related to, as yet largely unknown, differences in macromolecular composition. Macromolecular analysis using micro-FTIR may shed light on the preservation/decomposition process of palynomorphs. Raman microscopy is another spectroscopic method to observe the macromolecular structure and can obtain a micron- or submicron resolution. However, it is difficult to get good spectra due to emission of autofluorescence from targeted palynomorphs using light with short wavelengths (e.g., 532 nm laser). In this presentation, we present the results of both ATR-FTIR and micro-Raman analysis of the cyst of Alexandrium catenella/pacificum.
IR spectra of A. catenella/pacificum cysts are characterized by a dominant absorption band between 1200-1000 cm-1 and weak bands between 1450-1200 cm-1 and 1800-1600 cm-1. Cluster analysis of the IR spectra for wave lengths between 800-1800cm-1 suggest that the macromolecular structure of A. catenella/pacificum cysts is very close to cellulose. However, the highest peak in the spectra of A. catenella/pacificum cysts in the 1200-1000 cm-1 window is at ~1033cm-1 and lower than for cellulose (~1059 cm-1). The Raman spectra (with using a 785 nm laser) for these cysts show main peaks around 1050-1170 cm-1 and these overlap with those of cellulose. The Raman spectra of A. catenella/pacificum cyst also include the higher peaks around 1500-1200 cm-1 region and show a moderate peak at 898 cm-1, which are characteristics of polysaccharides with 1,6- and β-glucoside bonds, respectively. We therefore suggest that the macromolecules in the cyst of A. catenella/pacificum are composed of the polysaccharide with β-1,4-glucoside bonds including smaller number of β-1,6-glucoside bonds. These data suggest the cyst of A. catenella/pacificum is susceptible to decomposition by cellulase compared to other gonyaulacoid dinocysts.

European Centre for Environment and Human Health, Truro, UK.

^{Nick YOUNG1,2*, Richard A. SHARPE1,2,3, Rosa BARCIELA1,2,4, Gordon NICHOLS2, Keith DAVIDSON5, Elisa BERDALET6, Lora E. FLEMING1,2}

Marine harmful algal blooms and observed human health effects – what is the evidence?

<sup>1 European Centre for Environment and Human Health, Truro, UK
2 University of Exeter Medical School, Exeter, UK
3 Public Health, Cornwall, Truro, UK
4 Met Office, Exeter, UK
5 Scottish Association for Marine Science, Scottish Marine Institute, Oban, UK
6 Institute of Marine Sciences (CSIC), Passeig Marítim de la Barceloneta, Barcelona, Spain
* Ny252@exeter.ac.uk</sup>

Exposure to harmful algal blooms (HABs) can lead to well recognised acute patterns of illness in humans. We carried out a scoping review using established methodology to map the evidence for associations between marine HABs and observed both acute and chronic human health effects. A systematic and reproducible search of publications from 1985 until May 2019 was conducted using diverse electronic databases. Following de-duplication, 5301 records were identified, of which 380 were included in the final qualitative synthesis. Most studies (220; 57.9%) related to Ciguatera Poisoning. Anecdotal and case reports were the most frequent study types (242; 63.7%), whereas there were fewer formal epidemiological studies (35; 9.2%). Only four studies related to chronic exposure to HABs. Few studies reported the use of human specimens for confirmation of the cause of illness (32; 8.4%). This study highlighted gaps in the evidence base including a lack of formal surveillance and epidemiological studies, limited use of toxin measurements in human samples, and a scarcity of studies of chronic exposure. Future research and policy should provide a baseline understanding of the burden of human disease to inform the evaluation of the current and future impacts of climate change and HABs on human health.

Swedish Meteorological and Hydrological Institute, Norrköping, Sweden.

^{Bengt KARLSON1, Agneta ANDERSSON2, Anders F. ANDERSSON3, Sonia BRUGEL2, Krzysztof JURDZINSKI3, Mikael HEDBLOM4, Meike LATZ3, Markus LINDH4, Jenny LYCKEN4 and Anders TORSTENSSON4}

Diversity and distribution of pelagic dinoflagellates along a salinity gradient from the Baltic Sea to the Skagerrak based on a combination of metabarcoding and microscopy

^{1 Oceanographic Research, Swedish Meteorological and Hydrological Institute, Gothenburg, Sweden
2 Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
3 Department of Gene Technology, SciLifeLab, School of Biotechnology, KTH Royal Institute of Technology, Stockholm, Sweden
4 Oceanographic Services, Swedish Meteorological and Hydrological Institute, Gothenburg, Sweden}

The Baltic Sea area is located in Northern Europe. The area is strongly affected by anthropogenic eutrophication. In addition, long term changes in salinity and temperature are observed, likely due to climate change. The surface waters form a salinity gradient from c. 3-30 from the northernmost part, the Bothnian Bay, to the Skagerrak, which is part of the Greater North Sea. Dinoflagellates are important primary producers in the area. Some phycotoxin producing dinoflagellates cause problems for the mussel and oyster industry, mainly in the Skagerrak. High biomass blooms of Karenia mikimotoi and Karlodinium veneficum have caused fish mortalities. Other high biomass dinoflagellate blooms include Tripos spp., Lepidodinium sp. and Noctiluca scintillans. Plankton diversity and distribution have been investigated since the 1800s. In the beginning silk nets were used for sampling and light microscopy for analysis. During the last ~30 years tube sampling and concentration of samples using the sedimentation chamber method and analysis using inverted light microscopes (Utermöhl 1958) have been the dominating monitoring method. In a study aiming to investigate the usefulness of adding metabarcoding and high throughput sequencing as a monitoring tool, the diversity and distribution of Dinophyceae was investigated during year 2019 and part of 2020 based on the V4 region of 18S rDNA (primers according to Piredda et al. 2017). The PR2 database was used for annotating ASV’s (Guillou et al 2013). Preliminary results show that 10 different orders of Dinophyceae were observed using a combination of metabarcoding and the Utermöhl method. However, each method only resulted in observations of representatives of nine orders each. Microscopy resulted in observations of 35 genera while 18S metabarcoding revealed 79 annotated genera. At the species level the preliminary data show 73 species based on microscopy and 142 annotated species based on 18S metabarcoding. Additional aspects will be discussed.

References

Guillou, L. et al. 2013. The Protist Ribosomal Reference database (PR(2)): a catalog of unicellular eukaryote Small Sub-Unit rRNA sequences with curated taxonomy. Nucleic Acids Res. 41(Database issue), D597-D604. Version 4.14.0 25 June 2021

Piredda, R. et al. 2017. Diversity and temporal patterns of planktonic protist assemblages at a Mediterranean Long Term Ecological Research site. FEMS microbiology ecology 93(1), fiw200.

Utermöhl, H., 1958. Zur Vervollkomnung der quantitativen Phytoplankton-Methodik. Mitt. int. Ver. ther. angew. Limnol. 9, 1-38.

School of Earth and Ocean Sciences, University of Victoria, Canada.

^{Sandy MCLACHLAN1*, Vera POSPELOVA2,1 and Elaine C. HUMPHREY1}

Morphological variance within the spiniferate gonyaulacacean dinoflagellate cyst Cannosphaeropsis franciscana across the K/Pg boundary; the case for vesiculation as an ecophenotypic character with consideration for the genus Hafniasphaera

<sup>1 School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada
2 Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA
* sandyymcl@uvic.ca</sup>

The recent discovery of an Upper Cretaceous–lower Paleogene (upper Maastrichtian–lower Selandian) succession within the Oyster Bay Formation on eastern Vancouver Island, British Columbia, Canada, has been made based on dinoflagellate cyst biostratigraphic controls (McLachlan and Pospelova 2021). This recent work has presented the opportunity to analyze an unprecedent range of variation within an enigmatic spiniferate gonyaulacacean genus and species, Cannosphaeropsis franciscana (McLachlan et al. 2021). Using both transmitted light and scanning electron microscopy, we observe forms across a broad morphological plexus which encompasses differences in process type, autophragm geometry and most significantly, vesiculation. The presence and extent of cyst vesiculation is established as a key diagnostic character resulting in the erection of three subspecies: Cannosphaeropsis franciscana subsp. franciscana (autonym), Cannosphaeropsis franciscana subsp. vacuoseptata subsp. nov. and Cannosphaeropsis franciscana subsp. vesiculata subsp. nov. The onset and decline of vesiculate forms within the lowest Danian interval is grounds for the interpretation that the subspecies reflect an ecophenotypic response to changing paleoenvironmental factors above the K/Pg boundary, specifically those of unstable, stratified marine conditions associated with the post-Cretaceous transgressive phase. Assemblage data throughout the formation also reveal members of the vesiculate genus Hafniasphaera increase their abundances in nutrient-rich and likely stratified coastal waters when Spiniferites species are also abundant. The development of vesicles is suggested as an adaptation to prolong cyst buoyancy and slow descent in the water column. An extensive literature review considering all illustrated reports of formally recognized species belonging to the genera Cannosphaeropsis and Hafniasphaera is also presented alongside taxa chronostratigraphic ranges.

References

McLachlan, S.M.S., Pospelova, V. 2021. Dinoflagellate cyst-based paleoenvironmental reconstructions and phytoplankton paleoecology across the Cretaceous–Paleogene (K/Pg) boundary interval, Vancouver Island, British Columbia, Canada. Cretaceous Research 126, 104878, doi: 10.1016/j.cretres.2021.104878.

McLachlan, S.M.S., Pospelova, V., Humphrey, E.H. 2021. Vesiculation in the dinoflagellate cyst Cannosphaeropsis franciscana Damassa, 1979 across the K/Pg boundary (Vancouver Island, Canada) with implications for spiniferate gonyaulacacean taxonomy and ecophenotypy. Review of Palaeobotany and Palynology 292, 104452, doi: 10.1016/j.revpalbo.2021.104452.

Biology Department, Woods Hole Oceanographic Institution, USA.

^{Donald M. ANDERSON1, Evangeline FACHON1, Robert S. PICKART2, Peigen LIN2, Alexis D. FISCHER1, Mindy L. RICHLEN1, Victoria UVA1, Michael BROSNAHAN1, Leah MCRAVEN2, Frank BAHR2, Kathi LEFEBVRE3, Jacqueline M. GREBMEIER4, Seth DANIELSON5, Yihua LYU6, Yuri FUKAI7}

Evidence for massive and recurrent toxic blooms of Alexandrium catenella in the Alaskan Arctic

^{1 Biology Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA
2 Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA
3 Environmental and Fisheries Sciences Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 2725 Montlake Blvd. East, Seattle, WA 98112, USA
4 University of Maryland Center for Environmental Sciences, Chesapeake Biological Laboratory, Solomons, MD 20688, USA
5 College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks AK 99775, USA,
6 South China Sea Environmental Monitoring Center, State Oceanic Administration, Guangzhou 510300, P.R. China
7 Graduate School of Environmental Science, Hokkaido University, North 10 West 5, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan}

Among the organisms that spread into and flourish in Arctic waters with rising temperatures and sea ice loss are toxic algae, a group of harmful algal bloom (HAB) species that produce potent biotoxins. Alexandrium catenella, a cyst-forming dinoflagellate that causes paralytic shellfish poisoning (PSP) throughout the world, has been observed in Alaskan waters for decades and is known to be transported into Arctic regions in waters transiting northward through Bering Strait, yet there is little recognition of this organism as a human health concern north of the Strait. Here we describe an exceptionally large A. catenella benthic cyst bed and hydrographic conditions across the Chukchi Sea that support germination and development of recurrent, self-initiating, and self-seeding blooms. Two prominent cyst accumulation zones result from deposition promoted by weak circulation. Cyst concentrations are among the highest reported globally for this species and the cyst bed is at least 6X larger in area than any other. These extraordinary accumulations are attributed to repeated inputs from advected southern blooms and to localized cyst formation and deposition. Over the last two decades, warming has likely increased the magnitude of the germination flux two-fold and advanced the timing of cell inoculation into the euphotic zone by 20 days. Conditions are also now favorable for bloom development in surface waters. The region is poised to support annually recurrent A. catenella blooms that are unprecedented in scale, posing a significant and worrisome threat to public and ecosystem health in Alaskan Arctic communities where economies are subsistence based.

Department of Geology, Ghent University, Belgium.

^{Pjotr MEYVISCH1*, Pieter Roger GURDEBEKE1, Henk VRIELINCK2, Kenneth Neil MERTENS3, Gerard VERSTEEGH4, Katarzyna ŚLIWIŃSKA5, Stephen LOUWYE1}

Recent advances in infrared spectroscopy applied to single specimen dinoflagellate cysts: methodological framework and applications

<sub>1 Department of Geology, Ghent University, 9000 Ghent, Belgium
2 Department of Solid State Sciences, Ghent University, 9000 Ghent, Belgium
3 Ifremer, LITTORAL, F‐29900 Concarneau, France
4 Marine Biochemistry section, Alfred-Wegener-Institute, 27570 Bremerhaven, Germany
5 Department of Stratigraphy, GEUS, 1350 Copenhagen, Denmark
* pjotr.meyvisch@ugent.be</sub>

Fourier-transformed infrared (FTIR) spectroscopy is a spectrochemical technique able to retrieve macromolecular information from organic materials. When combined with a microscope (micro-FTIR), the (geo)chemical composition of single specimen dinoflagellate cysts (dinocysts) can be determined. Over the last decades a small number of dinocyst micro-FTIR studies booked often inconsistent results by overlooking important methodological aspects during analysis.
This study takes into account variables like sample preparation, specimen morphology and size and spectral data processing steps and presents a standardized method based on attenuated total reflectance (ATR) micro-FTIR spectroscopy which is able to collect robust spectral datasets. These datasets are largely devoid of nonchemical artifacts inherent to other infrared spectrochemical methods which have typically been used in similar studies in the past (i.e. transmission and transflection spectroscopy). Several guidelines are proposed which facilitate the collection and qualitative interpretation of highly reproducible and repeatable spectrochemical dinocyst data. These, in turn, pave the way for a systematic exploration of dinocyst chemistry and its assessment as a chemotaxonomical tool or proxy.
An ATR micro-FTIR case study on morphologically similar late Paleogene to early Neogene dinocysts Palaeocystodinium golzowense, Svalbardella clausii and Svalbardella cooksoniae is also presented, which highlights the chemotaxonomical potential of the method.

Climate Change Cluster (C3), University of Technology Sydney, New South Wales, Australia.

_{Michaela E. LARSSON1,2*, Anna R. BRAMUCCI1, Sinead COLLINS3, Gustaaf HALLEGRAEFF4, Tim KAHLKE1, Jean-Baptiste RAINA1, Justin R. SEYMOUR1, Martina A. DOBLIN1}

Mucospheres produced by the mixotrophic dinoflagellate Prorocentrum cf. balticum impact ocean carbon cycling

<sup>1 Climate Change Cluster (C3), University of Technology Sydney, New South Wales, Australia
2 Phytoplankton Ecology Unit, Department of Water and Environmental Regulation, Joondalup, Western Australia, Australia
3 Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
4 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, 7001, Australia
* Michaela.Larsson@uts.edu.au</sup>

Marine microbes govern ocean productivity and biogeochemistry, which ultimately regulates global climate (Falkowski et al., 1998). Mixotrophic protists (single celled eukaryotic organisms) that engage both phototrophy (photosynthesise) and phago-heterotrophy (engulfment of particles) (Flynn et al. 2019) – contribute substantially to energy fluxes and biogeochemical cycles because of their nutritional flexibility (Mitra et al. 2016), ability to occupy wide environmental niches (Edwards 2019; Ward et al. 2011), and influence on trophic dynamics (Caron 2016; Ward and Follows 2016). However, the degree to which this important functional group and their behaviours shape these global scale processes remains largely unquantified (Worden et al. 2015). In this seminar, we will reveal the feeding mechanism of the mixotrophic dinoflagellate, Prorocentrum cf. balticum, and describe the sophisticated foraging strategy it uses to attract, capture, and immobilise microbial prey. We will also discuss how this previously undescribed behaviour involving the production of carbon-rich mucoid structures we have termed ‘mucospheres’, represents an overlooked, yet potentially significant mechanism for oceanic carbon export.

References

• Falkowski, P.G., Barber, R.T., Smetacek, V., 1998. Biogeochemical controls and feedbacks on ocean primary production. Science 281, 200–206.
• Flynn, K.J. et al., 2019. Mixotrophic protists and a new paradigm for marine ecology: where does plankton research go now? Journal of Plankton Research 41, 375–391.
• Mitra, A. et al., 2016. Defining planktonic protist functional groups on mechanisms for energy and nutrient acquisition: incorporation of diverse mixotrophic strategies. Protist 167, 106–120.
• Edwards, K.F., 2019. Mixotrophy in nanoflagellates across environmental gradients in the ocean. Proceedings of the National Academy of Sciences 116, 6211–6220.
• Ward, B.A., Dutkiewicz, S., Barton, A.D., Follows, M.J., 2011. Biophysical aspects of resource acquisition and competition in algal mixotrophs. The American Naturalist 178, 98–112.
• Caron, D.A., 2016. Mixotrophy stirs up our understanding of marine food webs. Proceedings of the National Academy of Sciences 113, 2806–2808.
• Ward, B.A., Follows, M.J., 2016. Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux. Proceedings of the National Academy of Sciences 113, 2958–2963.
• Worden, A.Z. et al., 2015. Rethinking the marine carbon cycle: factoring in the multifarious lifestyles of microbes. Science 347.

Ifremer, DYNECO Centre de Brest, France.

^{Raffaele SIANO1*}

Back to the past: sedimentary archives revealed dinoflagellate communities shifts and species adaptations due to human impact in the Bay of Brest (France)

<sup>1 Ifremer, DYNECO Centre de Brest, France
* raffaele.siano@ifremer.fr</sup>

The study of dinoflagellate remains (viable and fossilised resting stages, sedimentary ancient DNA) across stratified layers of marine sediment cores allows the assessment of centuries-old community and population dynamics. When resting stages can be revived from ancient sediments and monoclonal strains are established and compared to contemporary ones, species physiological and genetic adaptation patterns evolved across time can be inferred. Environmental and experimental observations can be related to other paleo-ecological proxies, such as organic and inorganic pollutants, to determine whether the observed dinoflagellate community and species variations are an effect of human impact. In the Bay of Brest (Brittany, France) paleogenetic studies allowed ca. 1400 years of retrospective analyses of dinoflagellate community and harmful species. Heavy metal pollution traces in sediments ascribed to the World War II period coincided with irreversible dinoflagellate community shifts. After the war and especially from the 1980’s to 1990’s, dinoflagellate genera shift followed chronic contaminations of agricultural origin and the harmful species Alexandrium minutum progressively developed across the 20th century (Siano et al., 2021). In order to assess the physiological adaptations of modern populations to the increase in eutrophication and to the progressive phosphorous limitation that occurred in the area across the 20th century, resurrection ecology experiments were carried out on buried cysts of A. minutum and, for comparison, on Scrippsiella acuminata and S. donghaienis. Using a plant seed-inspired priming approach, 150-year old cyst revivification and an increase in the number of revived cells were obtained by stimulating germination using melatonin and gibberellic acid (Delebecq et al., 2020). Metabolomics profiles of A. minutum strains of the eutrophication (1980’s) and post-eutrophication period (2000’s) cultivated in P-depleted conditions were similar, conversely to those of S. donghaienis strains that were significantly different for 27 lipophilic compounds. However, when the alkaline phosphatase (AP) activity was measured at single cell level with an ad-hoc developed microfluidic systems and in P-depleted culture conditions, consistent differences were observed between strains of the pre-eutrophication (1940’s) and the beginning of the post-eutrophication period (1990’s), both in A. minutum and S. acuminata. For both species, total AP in the 1990’s decade was significantly lower than in the 1940’s. Considering that the AP is produced in P limitation, these results suggest that both species would have adapted to the decreasing concentration of phosphorus in the environment. Alexandrium minutum produced less AP, meaning that this species would perform better in P limitation, likely thriving upon internal phosphorous stocks, an adaption that would explain its ecological success in recent time in the Bay of Brest (Girault et al., 2021). These results suggest that the evolution of specific biological traits in dinoflagellate species is a key factor to explain multiannual species dynamics and that paleo-ecological approaches can help unveiling and understanding this process.

References

• Delebecq, G., Schmidt, S., Ehrhold, A., Latimier, M., Siano, R., 2020. Revival of ancient marine dinoflagellates using molecular biostimulation . Journal of Phycology 56, 1077–1089.
• Girault, M., Siano, R., Labry, C., Latimier, M., Jauzein, C., Beneyton, T., Buisson, L., Del Amo, Y., Baret, J.-C. (2021). Variable inter and intraspecies alkaline phosphatase activity within single cells of revived dinoflagellates. Isme Journal 15, 2057–2069.
• Siano, R., Lassudrie, M., Cuzin, P., Briant, N., Loizeau, V., Schmidt, S., Ehrhold, A., Mertens, K.N., Lambert, C., Quintric, L., Noël, C., Latimier, M., Quéré, J., Durand, P., Penaud, A., 2021. Sediment archives reveal irreversible shifts in plankton communities after World War II and agricultural pollution. Current Biology 31, 2682–2689.

MARUM, Center for Marine Environmental Sciences, University of Bremen, Germany.

^{Karin ZONNEVELD1*}

Where do dinoflagellate cysts in marine sediments come from?

<sup>1 MARUM, Center for Marine Environmental Sciences, University of Bremen, Leobener Str. 8,
28359 Bremen, Germany
* kzonneveld@marum.de</sup>

Finding the answer on this question is of major importance both in studies investigating the dynamics of harmful algal blooms as well as in paleo-environmental studies where fossilized cyst associations in sediments are being used to reconstruct past upper ocean environmental and oceanographic conditions at times of deposition.
To address this question it is important to know where dinoflagellate cysts are being produced in the upper water column and if and how they are laterally and/or vertically transported, dispersed and/or resuspended during the settling and embedding process. Despite increasing information about these processes in coastal environments, extremely little information is known from the open ocean.
To decrease this gap of information we used the excellent sea going facilities at the MARUM/University of Bremen to study the track of dinoflagellate cysts from their production towards embedding in sea floor sediments in the open ocean upwelling system off Cape Blanc (NW Africa). This region is characterised by permanent upwelling along the shelf break, bringing nutrient rich deep waters to the ocean surface. Furthermore frequent dust storms blow trace element rich Sahara sediments into the area. The combination of upwelling and dust input results in this area being one of the most productive regions in the world.
To study the production, vertical/lateral transport and embedding/resuspension of dinoflagellate cysts we collected the upper ocean cyst export production with free drifting traps that were placed in active upwelling cells and in a more offshore located upwelling filament. By following the traps several days with a daily collecting of cysts at three different water depths, information about the species succession was obtained. Cyst associations of the traps were compared to associations in selected deeper water layers (e.g. nepheloid layers) by in-situ pumps as well as surface sediments.
During this lecture I will present the results from our studies carried out at times of maximal upwelling intensity in November 2018 and, for the region, minimal upwelling intensity in August 2020. Results allow the recognition of both vertical and lateral transport of cysts in the water column during the settling process. Lateral transport of cysts in the region appeared related to the presence of nepheloid layers that origin at the shelf break and can be followed to about 130km offshore. Furthermore, the results show that at times of maximal upwelling, the deep ocean is spiced by resuspended cysts that origin at the coastal shelf area.

Laboratoire Géosciences Océans (LGO, UBO, IUEM, UMR 6538), Brest, France.

^{Vincent COUSSIN1, Aurélie PENAUD2, Nathalie COMBOURIEU-NEBOUT3, Odile PEYRON4, Sabine SCHMIDT5, Sébastien ZARAGOSI6, Yannick MIRAS7, Nathalie BABONNEAU8}

Marine and continental palynological evidence for the understanding of modern environments in the Western Mediterranean Sea (Algerian margin and Gulf of Lion)

^{1 Laboratoire Géosciences Océans (LGO, UBO, IUEM, UMR 6538), vincent.coussin@univ-brest.fr
2 Laboratoire Géosciences Océans (LGO, UBO, IUEM, UMR 6538), aurelie.penaud@univ-brest.fr
3 Histoire Naturelle de l’Homme Préhistorique (HNHP, MNHN, CNRS, UMR7194), nathalie.combourieu-nebout@mnhn.fr
4 Institut des Sciences de l’Evolution de Montpellier (ISEM, Université de Montpellier 2, CNRS, UMR 5554), odile.peyron@umontpellier.fr
5 Laboratoire Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC, Université de Bordeaux, CNRS, UMR 5808), sabine.schmidt@u-bordeaux.fr
6 Laboratoire Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC, Université de Bordeaux, CNRS, UMR 5808), sebastien.zaragosi@u-bordeaux.fr
7 Histoire Naturelle de l’Homme Préhistorique (HNHP, MNHN, CNRS, UMR7194), yannick.miras@mnhn.fr
8 Laboratoire Géosciences Océans (LGO, UBO, IUEM, UMR 6538), nathalie.babonneau@univ-brest.fr}

The Mediterranean Sea is generally described as an oligotrophic area where primary productivity is limited to few coastal environments characterized by nutrient-enriched fluvial inputs. However, several studies have shown that the Western Mediterranean hydrology presents major seasonal productive patterns linked to either large fluviatile inputs (e.g. Adriatic Sea under Po river plumes (Zonneveld et al., 2009) or seasonal upwelling cells (e.g. Alboran sea (Penaud et al., 2011). This study aims at: i) discussing the organic microfossil assemblages (pollen grains, dinoflagellate cysts and other non-pollen palynomorphs) from two different productive zones of the Western Mediterranean Sea as well as ii) underlining the interconnections between marine and continental influence responsible for marine and terrestrial palynomorph present-day spatial distributions. Samples from 25 sites collected from the Gulf of Lion and the Algerian Margin have been analysed in order to compare these two present-day noteworthy productive areas. Results highlight: i) the Gulf of Lion’s marine productivity driven by a conjunction of Rhône river inputs and seasonal upwelling mechanisms, ii) the strong productive pattern of the frontal meeting zone between Modified Atlantic Waters and Surface Mediterranean Waters (i.e. water density front mixings and related upwelling). Moreover, these two productive patterns are discussed at the light of major links allowing to understand continental (vegetation witnesses) and marine (sea-surface hydrological conditions) bio-indicators. This study will therefore allow to better interpret paleoenvironmental signatures derived from palynomorphs in Holocene studies from the Algerian Margin (MD04-2801; (Babonneau et al., 2012) and the Gulf of Lion (KCGC-31; (Bassetti et al., 2016) where palynological investigations have never been performed.

References

• Babonneau, N., Cattaneo, A., Savoye, B., Barjavel, G., Deverchere, J., Yelles, K., 2012. The Kramis fan offshore western Algeria: the role of sediment waves in turbiditic levee growth. SEPM Special Publication 99, 293–308.
• Bassetti, M., Berne, S., Sicre, M., Dennielou, B., Alonso, Y., Buscail, R., Jalali, B., Hebert, B., Menniti, C., 2016. Holocene hydrological changes of the Rhone River (NW Mediterranean) as recorded in the marine mud belt. Climate of the Past Discussions 1–31. https://doi.org/10.5194/cp-12-1539-2016
• Penaud, A., Eynaud, F., Sanchez Goñi, M., Malaizé, B., Jean Louis, T., Rossignol, L., 2011. Contrasting sea-surface responses between the western Mediterranean Sea and eastern subtropical latitudes of the North Atlantic during abrupt climatic events of MIS 3. Marine Micropaleontology 80, 1–17. https://doi.org/10.1016/j.marmicro.2011.03.002
• Zonneveld, K.A.F., Chen, L., Möbius, J., Mahmoud, M.S., 2009. Environmental significance of dinoflagellate cysts from the proximal part of the Po-river discharge plume (off southern Italy, Eastern Mediterranean). Journal of Sea Research 62, 189–213. https://doi.org/10.1016/j.seares.2009.02.003

Ludwig-Maximilians-Universität München, Germany.

^{Marc GOTTSCHLING1*}

The importance of the epitype concept for reliable species determination in protists such as dinophytes

<sup>1 Department Biologie: Systematik, Biodiversität und Evolution der Pflanzen, GeoBio-Center, Ludwig-Maximilians-Universität München, Menzinger Str. 67, D – 80 638 Munich, Germany
* gottschling@bio.lmu.de</sup>

Type material, particularly of older taxa, consists of specimens mounted permanently on glass or mica slides or of illustrations only. In many cases, type material is ambiguous and makes reliable species determination problematic. For a correct application of such ambiguous scientific names, the Shenzhen (‘botanical’) Code (ICN) provides a tool for designation of interpretative epitypes. The taxonomic identity of dinophytes is clarified by collecting samples at corresponding type localities. After establishing living strains, species are DNA-barcoded using rRNA sequences and investigated using contemporary light and scanning electron microscopy. Strains that are morphologically consistent with corresponding protologues are used for designation of interpretative epitypes. The significant difference from the historical types is that fully documented epitypes correspond to living material enabling DNA sequencing as well as experiments in ecology. Thus, epitypification is a key tool for a stable taxonomy and reliable species determination.

Limnological Institute, Siberian Branch of the Russian Academy of Sciences, Irkutsk.

^{Natalia ANNENKOVA1*}

Dinoflagellates, which live or probably live in the ancient Lake Baikal: single cell and DNA metabarcoding studies

<sup>1 Limnological Institute, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
* tasha.annenkova@gmail.com</sup>

Most molecular-genetic studies of freshwater protists correspond mainly to Northern Europe and North America. Lake Baikal is situated in the Eastern Siberia, Asia. It is the largest (by volume) and the oldest freshwater lake in the world. In contrast to its age of about 26 Myrs, our data suggest that a few known Baikal dinoflagellates are young species, which recently diverged from marine species. This makes them interesting objects to study speciation processes. At the same time our ongoing 18S rDNA metabarcoding studies reveal higher dinoflagellate diversity in the lake than previously was known. DNA fragments of Amoebophrya and Syndiniales were also found in Baikal. Of special interest is benthic species, because ancient Baikal taxa are commonly found within benthic community. However, analyzing DNA metabarcoding data we need to consider false-positive bias, which could be found in such data. Overall, dinoflagellate studies in Baikal region may help to feel the gaps in their phylogeography, as well as to provide a new knowledge about their adaptations to specific Baikal conditions.

Universitat de Barcelona, Spain.

^{Francesc RUBIÓ GARRIDO1* & Elisa BERDALET1}

Ostreopsis cf. ovata: A friendly dinoflagellate who likes to attach to different macroalgae and to a bryozoan

<sup>1 Institut de Ciències del Mar (CSIC), Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalonia, Spain
* franrubio96@gmail.com</sup>

Benthic toxic harmful algal bloom occurrence, and in particular, the proliferations of the species Ostreopsis cf. ovata, are becoming more frequent in temperate regions. O. cf. ovata recurrent blooms covering macroalgal communities have been reported in the last 20 years in the beach of Sant Andreu de Llavaneres (NW Mediterranean) during the summer fall period. The monitoring of these blooms in this beach has been conducted by sampling the dominant macroalgae, usually Jania spp. and Ellisolandia spp. However, to have a better understanding on the substrates to which O. cf. ovata attaches in this hot spot, the taxonomic characterization of the macroalgal communities was conducted during the 2019 and 2020 summers. In addition, in 2020 the O. cf. ovata bloom was monitored by sampling the above mentioned taxa as well as three abundant macroalgae, namely, Padina pavonica, Dictyota dichotoma and Halopteris scoparia and the bryozoan Amathia verticillata which appeared for the first time in that site.

In both sampled periods, the macroalgal communities were dominated by Corallinales species which formed turfs typical of non complex and degraded habitats, subjected to anthropogenic pressure (highly urbanized and eutrophic). Quantitatively, the cell concentrations of O. cf. ovata per fresh weight of the different substrates sampled in 2020 showed high variability along the bloom with the highest values estimated on Jania spp. and A. verticillata. Qualitatively, the general temporal trend of the 2020 bloom was pretty similar, independently of the sampled substrate, suggesting that any dominant macroalga can be appropriate to monitor an O. cf. ovata bloom. However, given that the absolute cell concentrations are used to ascertain the risk of the bloom to human health, more in depth studies of the links between O. cf. ovata and the benthic substrates are required.

Marine Biological Association of the UK, Plymouth, UK.

^{Linda K. MEDLIN1* Maria GAMELLA2, Gerardo MENGS3, Verónica SERAFÍN2, Susana CAMPUZANO2, José M. PINGARRÓN2}

Advances in the detection of toxic algae using electrochemical biosensors

<sup>1 Marine Biological Association of the UK, The Citadel, Plymouth, UK PL1 2PB
2 Department of Analytical Chemistry, Universidad Complutense de Madrid, E-28040 Madrid, Spain
3 Ecotoxilab, 28550 Madrid, Spain
* lkm@mba.ac.uk</sup>

Harmful algal blooms (HABs) are becoming more frequent as climate changes, with tropical toxic species moving northward, e.g. up the Iberian Peninsula. Monitoring programs, detecting the presence of toxic algae before they bloom, are of paramount importance to protect aquatic ecosystems, aquaculture, human health and local economies. Rapid and reliable species identification methods using molecular barcodes coupled to biosensor detection tools have received increasing attention as an alternative to the legally required but impractical standard microscopic counting-based techniques. Our electrochemical detection system for the determination of these toxic algae has been improved moving from the conventional sandwich hybridization protocols using different redox mediators and signaling probes modified with different labels to a novel strategy involving the recognition of heteroduplexes by selective commercial antibodies further labeled with bacterial antibody binding proteins conjugated with multiple enzyme molecules. Although each development has increased sensitivity, the most significant (a 100-fold increase in signal) has been produced with this latest strategy. Our newest results involve the use of magnetic microbeads (MBs) and amperometric detection at screen-printed carbon electrodes (SPCEs) to detect the RNA of our target toxic species. With these improvements, our current system is able to detect as low as 5 cells per liter for some species, by using a fast, simple and cheap methodology that can be integrated in easy-to-use portable systems. Our long-term goal is to apply this optimized protocol in a laboratory on a chip (LOC) with up to 200 electrodes for the simultaneous detection of all toxic species.

Université de Bordeaux, France.

^{Coralie ZORZI1,2* and Anne DE VERNAL1}

Paleoceanographical changes of the Plio-Pleistocene based on marine palynological approach at ODP Sites 882 and 887, western and eastern North Pacific

<sup>1 GEOTOP, Université du Québec à Montréal, Montréal, Canada
2 EPHE-EPOC, Université de Bordeaux, France
* coraliezorzi@gmail.com</sup>

The growth of glaciers in Alaska during the early Pliocene is in disagreement with the hypothesis suggesting that development of permanent continental ice in the circum-North Pacific is associated to onset of the modern halocline at 2.7 Ma (cf. Haug et al. 2005). However, the rarity of paleoceanography data documenting salinity in the eastern North Pacific prevents full understanding of the relationship between the halocline development and glaciers growth at regional scale. Numerical simulations have led to suggest that a strong contrast over the subarctic gyre during the Pliocene, with warm sea surface temperature (SST) in the east and cold SST in the west, might explain early ice extend in North America. Here again, the lack of paleoceanographic data is critical. In the view to fill this gap and to better constrain the scheme of the Plio-Pleisctocene climate-ocean-ice transition in the northern North Pacific region, we investigated the dinocyst assemblages at Ocean Drilling Program (ODP) Sites 882 and 887, located in the west and east respectively. Until 4.2 Ma, species associated with subpolar waters, Pyxidinopsis braboi, Filisphaera filifera and Impagidinium pallidum, are reported in the western Pacific. The presence of these species contrasts with the occurrence of Ataxiodinium zevenboomii, Impagidinium velorum and Impagidinium patulum in the Gulf of Alaska, which are associated with warm and temperate sea surface conditions. Between 4.2 and 2.7 Ma, the species assemblages at both sites are characterized by the dominance of the cold tolerant taxon Habibacysta tectata, which alternates with Impagidinium detroitense, and suggests homogenous cooling of the Pacific subarctic gyre until 2.7 Ma. After 2.7 Ma, dinocyst assemblages suggest temperate conditions and seasonal warming seat the surface due enhanced stratification, with the onset of the halocline. Concomitant extinction of Impagidinium detroitense, which marks a major biostratigraphical limit, is reported ~ 2.7 Ma at both ODP Sites 882 and 882, supports simultaneous onset of the modern halocline in the North Pacific. Dinocysts assemblages suggest the presence of warmer sea surface conditions in the Gulf of Alaska during the Pliocene and tend to support strong zonal contrast in the subarctic gyre prior to 4.2 Ma leading to early glaciers growth fostered by high evaporation and moisture supply in the east. However, our results also indicate a reduction of east-west gradient at 4.2 Ma, well before the development of the halocline at 2.7 Ma, which is recorded here for the first time in the Gulf of Alaska.

Université de Bordeaux, France.

^{Shauna MURRAY1*}

Ciguatera Fish Poisoning and Gambierdiscus species in Australia and the Pacific

<sup>1 University of Technology Sydney, School of Life Sciences, PO Box 123 Broadway NSW 2007, Australia
* Shauna.Murray@uts.edu.au</sup>

Ciguatera Fish Poisoning (CFP) is an illness caused by the accumulation of Ciguatera Toxins (CTX) produced by certain species of Gambierdiscus in edible fish. It is common in Australia and the wider Pacific region. In Australia, > 1400 cases and two fatalities were reported over a ~45 year period, with an estimated reporting rate of ~10%, indicating ~300 cases occur annually. Prior to 2014, only one CFP event was linked to a fish caught south of Queensland (29°S). Since then, 26 cases of CFP have occurred in more southerly regions, including a fish caught at Crowdy Head (32°S), the most southerly reported fish containing CTXs. The warming East Australian Current and its southward intrusion appears linked to the increased and more southerly distribution of CFP.
This expanding public health threat has highlighted the need to assess our knowledge of CFP, CTXs Gambierdiscus in Australia and the Pacific. Since 1991, when the first Gambierdiscus spp. from Australia were isolated and cultured, knowledge of the diversity and CTX production of Gambierdiscus has greatly expanded. Few Gambierdiscus species cultured worldwide produce P-CTX 4A, 4B, 3C, which are the analogs known to bioconvert to P-CTX-1B in the presence of fish liver enzymes. In Pacific countries neighbouring Australia, such as the Cook Islands and French Polynesia, the species G. polynesiensis consistently produces high levels of P-CTX 4A, 4B, 3C, and its abundance has been significantly positively correlated with CFP incidences in reef fish.
In Australia, four new Gambierdiscus species have been found (G. lapillus, G. honu, G. holmesi, G. lewisii) and these and other species found (G. carpenteri, Fukuyoa spp.) do not produce known CTXs. However, relatively few studies have been conducted. This work will build on our knowledge of CTX causative and vector species to provide the information needed to manage increasing risks of CFP in Australia.