Abstracts

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

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

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

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 Greenhough1,2, Craig Waugh1, Roel van Ginkel1, Joel Bowater1, Gurmeet Kaur1, Joy Oakly1, Maxence Plouviez1, Richard A. Ingebrigtsen1, Johan Svenson1, Andrew I Selwood1, Kirsty F Smith1, Chris M Brown2, Julien Vignier1, Nathan J Kenny2, Anne Rolton1}

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.

Recent progress and emerging tools in athecate dinoflagellate classification and phylogeny

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

^{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.

High Arctic late Paleocene and early Eocene dinoflagellate cysts

^{Appy Sluijs1 and Henk Brinkhuis1,2}

<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.

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

^{Y. Cho1, S. Hidema2, T. Omura3, K. Koike4, K. Koike5, S. Tsuchiya1, K. Konoki1, Y. Oshima6#, M. Yotsu-Yamashita1}

^{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.