Abstracts

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.