Elevated temperature as the dominant stressor on the harmful algal bloom-causing dinoflagellate Prorocentrum obtusidens in a future ocean scenario.

Marine dinoflagellates are increasingly affected by ongoing global climate changes. While understanding of their physiological and molecular responses to individual stressors anticipated in the future ocean has improved, their responses to multiple concurrent stressors remain poorly understood. Here, we investigated the individual and combined effects of elevated temperature (26 °C relative to 22 °C), increased pCO2 (1000 µatm relative to 400 µatm), and high nitrogen: phosphorus ratio (180:1 relative to 40:1) on a harmful algal bloom-causing dinoflagellate Prorocentrum obtusidens under short-term (28 days) exposure. Elevated temperature was the most dominant stressor affecting P. obtusidens at physiological and transcriptomic levels. It significantly increased cell growth rate and maximum photosynthetic efficiency (Fv/Fm), but reduced chlorophyll a, particulate organic carbon, particulate organic nitrogen, and particulate organic phosphorus. Elevated temperature also interacted with other stressors to produce synergistic positive effects on cell growth and Fv/Fm. Transcriptomic analysis indicated that elevated temperature promoted energy production by enhancing glycolysis, tricarboxylic acid cycle, and nitrogen and carbon assimilation, which supported rapid cell growth but reduced material storage. Increased pCO2 enhanced the expression of genes involved in ionic acid-base regulation and oxidative stress resistance, whereas a high N:P ratio inhibited photosynthesis, compromising cell viability, although the effect was alleviated by elevated temperature. The combined effect of these multiple stressors resulted in increased energy metabolism and up-regulation of material-synthesis pathways compared to the effect caused by elevated temperature alone. Our results underscore ocean warming as the predominant stressor for dinoflagellates and highlight the complex, synergistic effects of multi-stressors on dinoflagellates.

The effects of polystyrene microplastics on feeding, growth, and trophic upgrading of protozoan grazers.

Microplastics have become ubiquitous in the global marine environment, posing substantial influences on marine organism health, food web function and marine ecosystem structure. Protozoan grazers are known for their ability to improve the biochemical constituents of poor-quality algae for subsequent use by higher trophic levels. However, the effects of microplastics on the trophic upgrading of protozoan grazers remain unknown. To address this knowledge gap, the ciliate Euplotes vannus and the heterotrophic dinoflagellate Oxyrrhis marina were exposed to microplastic particles (5 µm) for four days with various concentrations (1-20 mg/L). Both O. marina and E. vannus ingested microplastics. At the exposure level of 20 mg/L, the ingestion rate, growth rate, biovolume, and carbon biomass of E. vannus were significantly decreased by 28.18 %, 32.01 %, 30.46 %, and 82.27 %, respectively, while such effects were not observed for O. marina. The contents of highly unsaturated fatty acids in O. marina and E. vannus on a mixed diet of microplastic particles and green algae significantly reduced by 8.66 % and 41.49 % relative to feeding only on green algae, respectively. Besides, we also observed an increase in the composition of C18:3 (ω-3) and C20:3 (ω-3) concurrence with a significant decrease in C16:0 and C18:0 in E. vannus after 96 h exposure at 20 mg/L. These results indicate that microplastics can weaken trophic upgrading of the nutritional quality by protozoan grazers, which may consequently alter the function of food webs.

Geographic distribution of modern dinoflagellate cysts in surface sediments of the Arabian Sea: significance of taxa and morphometry as potential ecological indicators.

Studies on dinoflagellate cysts in the Arabian Sea (AS) are limited to the coastal waters, but no information from the deeper depths. The dinoflagellate cyst assemblages in surface sediment samples (0-2 cm) from the deeper depths (up to ~ 4500 m) of central (oxygen minimum zone (OMZ)) and southeastern (oligotrophic) AS revealed that the relatively good numbers of cyst concentrations reach deeper depths of OMZ (3505 m) and oligotrophic (4368 m) regions, but the former harbored more cyst concentrations than the latter. The cyst concentration and species count (including HAB species) recorded here are lower compared to the eastern (EAS) and western (WAS) AS, but the autotrophic cyst dominance (74-83%) at deeper depths is in contrast with the heterotrophic dominance in coastal AS. Of the recorded 41 cyst species (belonging to 18 genera), four species (cyst of Cladopyxis sp., Operculodinium janduchenei, Stelladinium bifurcatum, and Protoperidinium monospinum) from the deepest part of oligotrophic AS form the first report. In contrast, Spiniferites and Lingulodinium cysts were common occurrences. Taxonomic comparison with literature revealed (i) the prevalence of more cosmopolitan species (32 species) which could be due to the prevalence of large and small-scale lateral transport of cysts in oligotrophic regions followed by OMZ and coastal regions, respectively, and (ii) very few region-specific species, i.e., cyst of Protoperidinium latissimum, Lejeunecysta sabrina, cyst of Protoperidinium denticulatum in EAS and Impagidinium patulum, and I. strialatum, in WAS. Interestingly, variability in the morphometry was evident between the coastal and open oceans in some cosmopolitan cysts, e.g., Operculodinium centrocarpum and Lingulodinium machaerophorum. These findings from the less studied pelagic regions will contribute to the growing knowledge of dinoflagellate cyst distribution patterns and highlight the significance of cyst taxa and morphology as potential ecological indicators for AS.

Modification of the Trizol Method for the Extraction of RNA from Prorocentrum triestinum ACIZ_LEM2.

In samples of harmful algal blooms (HABs), seawater can contain a high abundance of microorganisms and elemental ions. Along with the hardness of the walls of key HAB dinoflagellates such as Prorocentrum triestinum, this makes RNA extraction very difficult. These components interfere with RNA isolation, causing its degradation, in addition to the complex seawater properties of HABs that could hinder RNA isolation for effective RNA sequencing and transcriptome profiling. In this study, an RNA isolation technique was established through the modification of the Trizol method by applying the Micropestle System on cell pellets of P. triestinum frozen at -20 °C, obtained from 400 mL of culture with a total of 107 cells/mL. The results of the modified Trizol protocol generated quality RNA samples for transcriptomics sequencing, as determined by their measurement in Analyzer Agilent 4150.

Discharge of ballast residual sediments during de-ballasting procedures: A more realistic estimate of propagule pressure.

Ship ballast residual sediments are an important vector of introduction for non-indigenous species. We evaluated the proportion of residual sediments and associated organisms released during de-ballasting operations of a commercial bulk carrier and estimated a total residual sediment accumulation of ∼13 t, with accumulations of up to 20 cm in some tank areas that had accumulated over 11 years. We observed interior hull-fouling (anemones, hydrozoans, and bryozoans) and high abundances of viable invertebrate resting stages and dinoflagellate cysts in sediments. Although we determined that <1 % of residual sediments and associated resting stages were resuspended and released into the environment during individual de-ballasting events, this represents a substantial inoculum of 21 × 107 viable dinoflagellate cysts and 7.5 × 105 invertebrate resting stages with many taxa being nonindigenous, cryptogenic, or toxic/harmful species. The methods used and results will help estimate propagule pressure associated with this pathway and will be relevant for residual sediments and nonindigenous species management.

Morphological, Toxicological, and Biochemical Characterization of Two Species of Gambierdiscus from Bahía de La Paz, Gulf of California.

We describe five new isolates of two Gambierdiscus species from Bahía de La Paz in the southern Gulf of California. Batch cultures of Gambierdiscus were established for morphological characterization using light microscopy (LM) and scanning electron microscopy (SEM). Pigment and amino acid profiles were also analyzed using high-performance liquid chromatography (HPLC-UV and HPLC-DAD). Finally, toxicity (CTX-like and MTX-like activity) was evaluated using the Artemia salina assay (ARTOX), mouse assay (MBA), marine fish assay (MFA), and fluorescent receptor binding assay (fRBA). These strains were identified as Gambierdiscus cf. caribaeus and Gambierdiscus cf. carpenteri. Toxicity for CTX-like and MTX-like activity was confirmed in all evaluated clones. Seven pigments were detected, with chlorophyll a, pyridine, Chl2, and diadinoxanthin being particularly noteworthy. For the first time, a screening of the amino acid profile of Gambierdiscus from the Pacific Ocean was conducted, which showed 14 amino acids for all strains except histidine, which was only present in G. cf. caribeaus. We report the presence of Gambierdiscus and Fukuyoa species in the Mexican Pacific, where ciguatera fish poisoning (CFP) cases have occurred.

Inactivation in vitro of the marine parasite Amyloodinium ocellatum.

The ectoparasite Amyloodinium ocellatum is a dinoflagellate that causes severe morbidity and mortality in both brackish and marine warmwater aquaculture fishes worldwide. A. ocellatum has a triphasic life cycle based on a free-living flagellate (the dinospore), a parasitic stage (the trophont) and a resting and reproductive cyst (the tomont). Current chemical treatments have shown some efficacy in eliminating dinospores but fail to inactivate the tomonts. Here we evaluated the efficacy of alternative treatments in vitro through sporulation tests and the quantification of dinospore production and motility. Hydrogen peroxide and peracetic acid efficiently decreased dinospore production at low concentrations, but total inactivation of tomonts was only achieved with higher dosages. Tomont inactivation was also observed with disinfectants such as sodium hypochlorite and Virkon S. This work provides insights into effective and environmentally friendly alternatives for the elimination of resistant forms of the marine parasite A. ocellatum.

Bioactivity of Amphidinol-Containing Extracts of Amphidinium carterae Grown Under Varying Cultivation Conditions.

Microalgae are of great interest due to their ability to produce valuable compounds, such as pigments, omega-3 fatty acids, antioxidants, and antimicrobials. The dinoflagellate genus Amphidinium is particularly notable for its amphidinol-like compounds, which exhibit antibacterial and antifungal properties. This study utilized a two-stage cultivation method to grow Amphidinium carterae CCAP 1102/8 under varying conditions, such as blue LED light, increased salinity, and the addition of sodium carbonate or hydrogen peroxide. After cultivation, the biomass was extracted and fractionated using solid-phase extraction, yielding six fractions per treatment. These fractions were analyzed using Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS/MS) to identify their chemical components. Key amphidinol compounds (AM-B, AM-C, AM-22, and AM-A) were identified, with AM-B being the most abundant in Fraction 4, followed by AM-C. Fraction 5 also contained a significant amount of AM-C along with an unknown compound. Fraction 4 returned the highest antimicrobial activity against the pathogens Staphylococcus aureus, Enterococcus faecalis, and Candida albicans, with Minimal Biocidal Concentrations (MBCs) ranging from 1 to 512 µg/mL. Results indicate that the modulation of both amphidinol profile and fraction bioactivity can be induced by adjusting the cultivation parameters used to grow two-stage batch cultures of A. carterae.

Sub-lethal effects of metals and pesticides on the freshwater dinoflagellate Palatinus apiculatus and environmental implications.

Microalgae are unicellular, photosynthetic organisms in aquatic environments and are sensitive to water quality and contaminants. While green algae and diatoms are widely used for toxicity assessments, there is a relatively limited amount of toxicity data available for freshwater dinoflagellates. Here, we evaluated the sub-lethal effects of the metals Cu, Cr, Ni, and Zn and the herbicides atrazine and S-metolachlor on the freshwater dinoflagellate Palatinus apiculatus. Based on the 72-h median effective concentration (EC50), P. apiculatus showed sensitive responses to metals in the order of Cu (0.052 mg L-1), Cr (0.085 mg L-1), Zn (0.098 mg L-1), and Ni (0.13 mg L-1). Among the tested herbicides, P. apiculatus was more sensitive to atrazine (0.0048 mg L-1) than S-metolachlor (0.062 mg L-1). In addition, we observed morphological alterations and significant increases in reactive oxygen species (ROS) production in cells exposed to 0.05 mg L-1 of Cu and 0.005 mg L-1 of atrazine. These indicated that metals and pesticides induced oxidative stress in cellular metabolic processes and consequently caused severe physiological damage to the cells. Our results provide baseline data on the toxic effects of typical environmental contaminants on freshwater dinoflagellate, suggesting that P. apiculatus could be used as a bioindicator in freshwater toxicity assessments. PRACTITIONER POINTS: The sub-lethal effects of metals and pesticides on the freshwater dinoflagellate Palatinus apiculatus were evaluated. Palatinus sensitively responded to metals and pesticides; of test chemicals, atrazine (0.0048 mg L-1 of EC50) was the most sensitive. Metals and pesticides induced oxidative stress and consequently caused severe physiological damage to the Palatinus cells. The freshwater dinoflagellate Palatinus can be used as a bioindicator in freshwater toxicity assessments.

The Ciliate Euplotes balteatus Exhibits Removal Capacity upon the Dinoflagellates Karenia mikimotoi and Prorocentrum shikokuense.

The significant threat posed by the ichthyotoxic dinoflagellate Karenia mikimotoi to coastal aquaculture, resulting in substantial economic losses, underscores the need for control and mitigation strategies. Bio-mitigation of algal blooms through grazers presents advantages in sustainability compared to methods relying on chemical or physical procedures. This study explored the inhibitory effect of nine Euplotes spp. (Alveolata, Ciliophora) isolates on simulated blooms, with E. balteatus W413 displaying removal capacity for K. mikimotoi and robust growth in co-cultivation. The unique size plasticity in W413 revealed an efficient predation strategy, as an increase in cellular size enables it to shift prey from bacteria to algal cells. The enlarged cell volume facilitates W413 to accommodate more algal cells, bestowing it with a high ingestion rate and removal capacity upon K. mikimotoi. Furthermore, W413 exhibited considerable inhibition towards co-occurring bloom species, specifically Prorocentrum shikokuense and Karenia spp., implying its potential to mitigate mixed-species blooms. The study enhances our understanding of the prey selectivity of Euplotes species and proposes E. balteatus as a potential bio-mitigation candidate for K. mikimotoi blooms, emphasizing the significance of micro-grazers in marine ecosystems.

Long-term changes in spatiotemporal distribution of Noctiluca scintillans in the southern North Sea.

To assess the spatiotemporal evolution of the heterotrophic dinoflagellate Noctiluca scintillans in the North Sea, the Helgoland Roads time series and Continuous Plankton Recorder survey were analysed using generalized additive models. Over the last decades, blooms of N. scintillans have occurred more frequently and intensively in many regions. This harmful algal bloom forming species can alter food webs, reduce ecosystem productivity, and lead to economic losses while causing lower aquacultural yields. After the 1990s, N. scintillans abundances have significantly increased by 1.65-fold and a significant prolongation of the bloom window was found (from 27.5 to 98 days in recent decades) off the island of Helgoland, Germany. Significant correlations were found between bloom initiation and nutrients, as well as light availability since these factors lead to increased prey availability. Highest abundances of N. scintillans were associated with water temperatures around 17 °C and wind speed below 6 ms-1 causing dense surface accumulations. Solar radiation of more than 200 Wm-2 was identified as a main driver for post-bloom conditions as it can deteriorate the cells and lead to the decline of N. scintillans abundances. In the southern North Sea, N. scintillans occurrences have intensified and spread since the 1980s with hotspots identified as the coastal waters adjacent to the estuaries of the Elbe and Rhine rivers.

Molecular monitoring of Dinophysis species assemblage in mussel farms in the Northwestern Adriatic Sea.

Several Dinophysis species can produce potent lipophilic toxins that pose a risk to human health when contaminated seafood is consumed, especially filter-feeding bivalve mussels. In the mussel farms of the Northwestern Adriatic Sea, seawater and seafood are regularly monitored for the presence of Dinophysis species and their associated toxins, but the current methodological approaches, such as light microscopy determinations, require a long time to make results available to local authorities. A molecular qPCR-based assay can be used to quantify various toxic Dinophysis species in a shorter timeframe. However, this approach is not currently employed in official testing activities. In this study, field samples were collected monthly or bi-weekly over one year from various mussel farms along the Northwestern Adriatic coast. The abundance of Dinophysis species in the seawater was determined using both traditional microscopy and qPCR assays. In addition, the concentration of lipophilic toxins for DSP in mussel flesh was quantified using LC-MS/MS focusing on the okadaic acid group. Dinophysis spp. site-specific single cells were isolated and analysed by qPCR yielding a mean rDNA copy number per cell of 1.21 × 104 ± 1.81 × 103. The qPCR assay gave an efficiency of 98 % and detected up to 10 copies of the rDNA target gene. The qPCR and light microscopy determinations in environmental samples showed a significant positive correlation (Spearman rs = 0.57, p-value < 0.001) with a ratio of 2.24 between the two quantification methods, indicating that light microscopy estimates were generally 44.6 % lower than those obtained by the qPCR assay. The qPCR approach showed several advantages such as rapidity, sensitivity and efficiency over conventional microscopy analysis, showing its potential future role in phytoplankton monitoring under the Official Controls Regulations for shellfish.

Co-occurrence between key HAB species and particle-attached bacteria and substrate specificity of attached bacteria in the coastal ecosystem.

The ecological dynamics of particle-attached bacteria (PAB) were observed through changes in the core phytoplankton phycosphere, and were associated with the dynamics of free-living bacteria (FLB) using metabarcoding and microscopic analyses over 210 days (with weekly sampling intervals) in the Jangmok coastal ecosystem, South Korea. Cluster analysis and non-metric multidimensional scaling classified the phytoplankton community into six groups comprising core phytoplankton species, including the harmful algal species Akashiwo sanguinea (dinoflagellate) in late autumn, Teleaulax amphioxeia (cryptomonads) in early winter and spring, Skeletonema marinoi-dohrnii complex (diatom) in winter, Pseudo-nitzschia delicatissima (diatom) in early spring, and diatom complexes such as Chaetoceros curvisetus and Leptocylindrus danicus in late spring. We identified 59 and 32 indicators in PAB and FLB, respectively, which rapidly changed with the succession of the six core phytoplankton species. The characteristics of PAB were mainly divided into "Random encounters" or "Attraction of motivation by chemotaxis." When Akashiwo sanguinea bloomed, bacteria of the genera Kordiimonas and Polaribacter, which are commonly observed in PAB and FLB, indicated "Random encounter" characteristics. In addition, Sedimenticola of PAB was uniquely presented in Akashiwo sanguinea, exhibiting characteristics of "Attraction of motivation by chemotaxis." In contrast, FLB followed the strategy of "Random encounters" because it was not affected by specific habitats and energy sources. Thus, many common bacteria were PAB and FLB, thereby dictating the bacteria's strategy of "Random encounters." "Attraction of motivation by chemotaxis" has characteristics of the species-specific interactions between PAB and specific harmful algal species, and is potentially influenced by organic matter of core phytoplankton cell surface and/or EPS released from phytoplankton.

Phylogeny and ultrastructure of a non-toxigenic dinoflagellate Amphidoma fulgens sp. nov. (Amphidomataceae, Dinophyceae), with a wide distribution across Asian Pacific.

Amphidoma languida, a marine thecate dinoflagellate that produces the lipophilic toxin azaspiracids (AZAs), is primarily found in the Atlantic. Although this species has not been recorded in the Asian Pacific, environmental DNAs related to Am. languida have been widely detected in the region by metabarcoding analysis. Their morphology and AZA production remain unclear. In this study, the morphology, ultrastructure, phylogeny, and AZA production of nine Amphidoma strains isolated from Japan, Malaysia, and Philippines were investigated. Phylogenetic trees inferred from rDNAs (SSU, ITS, and LSU rDNA) showed monophyly of the nine Pacific strains and were sister to the Am. languida clade, including the toxigenic strains from the Atlantic. Cells were ellipsoid, 8.7-16.7 µm in length and 7.4-14.0 µm in width, with a conspicuous apical pore complex. A large nucleus in the hyposome, parietal chloroplast with a spherical pyrenoid in the episome, and refractile bodies were observed. Thecal tabulation was typical of Amphidoma, Po, cp, X, 6', 6'', 6C, 5S, 6''', 2''''. A ventral pore was located on the anterior of 1' plate, beside the suture to 6' plate. The presence of a ventral depression, on the anterior of anterior sulcal plate, was different from Am. languida. A large antapical pore, containing approximately 10 small pores, was observed. Cells were apparently smaller than Am. trioculata, a species possessing three pores (ventral pore, ventral depression, and antapical pore). TEM showed the presence of crystalline structures, resembling guanine crystals, and cytoplasmic invaginations into the pyrenoid matrix. Flagellar apparatus lacking the striated root connective is similar to peridinioids and related dinoflagellates. AZAs were not detected from the Pacific strains by LC-MS/MS. This non-toxigenic Amphidoma species, here we propose as Amphidoma fulgens sp. nov., is widely distributed in the Asian Pacific. Moreover, molecular comparison also suggested that most of the environmental DNA sequences previously reported as Am. languida or related sequences from the Asian Pacific were attributable to Am. fulgens.

Determining ecological interactions of key dinoflagellate species using an intensive metabarcoding approach in a semi-closed coastal ecosystem of South Korea.

Marine phytoplankton communities are pivotal in biogeochemical cycles and impact global climate change. However, the dynamics of the dinoflagellate community, its co-occurrence relationship with other eukaryotic plankton communities, and environmental factors remain poorly understood. In this study, we aimed to analyze the temporal changes in the eukaryotic plankton community using a 18S rDNA metabarcoding approach. We performed intensive monitoring for 439 days at intervals of three days during the period from November 2018 to June 2020 (n = 260) in Jangmok Bay Time-series Monitoring Site in South Korea. Among the 16,224 amplicon sequence variants (ASVs) obtained, dinoflagellates were the most abundant in the plankton community (38 % of total relative abundance). The dinoflagellate community was divided into 21 groups via cluster analysis, which showed an annually similar distribution of low-temperature periods. Additionally, we selected 11 taxa that had an occurrence mean exceeding 1 % of the total dinoflagellate abundance, accounting for 93 % of the total dinoflagellate community: namely Heterocapsa rotundata, Gymnodinium sp., Akashiwo sanguinea, Amoebophrya sp., Euduboscquella sp., Spiniferites ramosus, Dissodinium pseudolunula, Sinophysis sp., Karlodinium veneficum, and Katodinium glaucum. The key dinoflagellate species were well represented at temporally variable levels over an entire year. Heterocapsa rotundata was not significantly affected by water temperature, whereas its dynamics were largely influenced by strong predation pressure, competition, and/or the supplementation of food sources. The growth of A. sanguinea was associated with dissolved inorganic phosphorus concentrations, while Euduboscquella sp. showed a significant relationship with D. pseudolunula and K. glaucum, largely representing a positive association that implies possible parasitic mechanisms. This study demonstrated interactions between key dinoflagellate species and the environment, as well as parasites, predators, competitors, and feeders.

Allelochemicals determine competition and grazing control in Alexandrium catenella.

The production of allelochemicals by the toxigenic dinoflagellate Alexandrium catenella is one of the suggested mechanisms to facilitate its bloom formation and persistence by outcompeting other phototrophic protists and reducing grazing pressure. In Southern California, toxic events caused by A. catenella and paralytic shellfish toxins (PSTs) regularly impact coastal ecosystems; however, the trophic interactions and mechanisms promoting this species in a food web context are still not fully understood. In the present study, we combined a dynamical mathematical model with laboratory experiments to investigate potential toxic and allelochemical effects of an A. catenella strain isolated off the coast of Los Angeles, Southern California, on competitors and a common zooplankton consumer. Experiments were conducted using three toxigenic strains of A. catenella, comparing the new Californian isolate (Alex Cal) to two strains previously described from the North Sea, a lytic (Alex2) and non-lytic (Alex5) strain, testing for donor density-dependent effects on two phytoplankton species (Rhodomonas salina, Tetraselmis sp.) and on the rotifer Brachionus plicatilis. Bioassays revealed a steep decline in competitor and consumer populations with increasing Alex Cal concentrations, indicating an intermediate lytic activity compared to the North Sea strains (lytic Alex2 and non-lytic Alex5). The rotifer fed and grew well on the PST- toxic, but non-lytic Alex5 strain, while its survival significantly decreased with increasing concentrations of the two lytic strains Alex Cal and Alex 2, indicating that negative effects on the rotifer were mediated by allelochemicals rather than PST-toxins. Mixed culture experiments including both competitors and consumers demonstrated that the intensity of allelochemical effects not only depended on the A. catenella density but also on the target density. Negative effects on grazers were alleviated by co-occurring competitors with a lower sensitivity to allelochemicals, thus reducing harmful compounds and allowing grazing control on the dinoflagellate to come into effect again. Results from mixed culture experiments were supported by the mathematical approach used in this study which was calibrated with data from simple monoculture growth, pairwise competition and predator-prey experiments, demonstrating the applicability of this model approach to predict the outcome of more complex food web dynamics at the community level.

An effective algaecide for the targeted destruction of Karenia brevis.

We address the targeted destruction of Karenia brevis using the algaecide calcium peroxide, in tandem with the flocculation and sinking of the species. The specific aspect of the approach is the incorporation of the algaecide within the floc to rapidly kill K. brevis, thus minimizing escape of cells from the floc and reentry to the water column. CaO2 gradually produces H2O2, which diffuses through cell membranes and induces oxidative stress, leading to cell death via excessive reactive oxygen species (ROS) formation. The effect of varying doses of calcium peroxide on K. brevis cells was measured with pulse amplitude modulated fluorometry and indicated that doses as low as 30 mg/L when integrated into flocs are effective in suppressing photosynthesis. Cell viability assays also indicate that such low levels are sufficient to cause cell death in a 3-6 hour time period. Thus, the proposed technology involving the incorporation of calcium peroxide in a cationic flocculating agent (polyaluminum chloride, PAC) leads to an inexpensive and scalable technology to mitigate harmful algal blooms of K. brevis.

Toxic effects of the emerging Alexandrium pseudogonyaulax (Dinophyceae) on multiple trophic levels of the pelagic food web.

The dinoflagellate Alexandrium pseudogonyaulax, a harmful algal bloom species, is currently appearing in increasing frequency and abundance across Northern European waters, displacing other Alexandrium species. This mixotrophic alga produces goniodomins (GDs) and bioactive extracellular substances (BECs) that may pose a threat to coastal ecosystems and other marine resources. This study demonstrated the adverse effects of A. pseudogonyaulax on four marine trophic levels, including microalgae (Rhodomonas salina), microzooplankton (Polykrikos kofoidii) and mesozooplankton (Acartia tonsa), as well as fish gill cells (RTgill-W1, Oncorhynchus mykiss), ultimately leading to enhanced mortality and cell lysis. Furthermore, cell-free supernatants collected from A. pseudogonyaulax cultures caused complete loss of metabolic activity in the RTgill-W1 cell line, indicating ichthyotoxic properties, while all tested GDs were much less toxic. In addition, cell-free supernatants of A. pseudogonyaulax led to cell lysis of R. salina, while all tested GDs were non-lytic. Finally, reduced egg hatching rates of A. tonsa eggs exposed to cell-free supernatants of A. pseudogonyaulax and impaired mobility of P. kofoidii and A. tonsa exposed to A. pseudogonyaulax were also observed. Altogether, bioassay results suggest that the toxicity of A. pseudogonyaulax is mainly driven by BECs and not by GDs, although further research into factors modulating the lytic activity of Alexandrium spp. are needed.

Sterolysin from a 1950s culture of Karlodinium veneficum (aka Gymnodinium veneficum Ballantine) forms lethal sterol dependent membrane pores.

In 1957 Abbott and Ballantine described a highly toxic activity from a dinoflagellate isolated from the English Channel in 1949 by Mary Park. From a culture maintained at Plymouth Laboratory since 1950, we have been able to isolate two toxic molecules (abbotoxin and 59-E-Chloro-abbotoxin), determine the planar structures by analysis of HRMS and 1D and 2D NMR spectra, and found them to be karlotoxin (KmTx) congeners. Both toxins kill larval zebrafish with symptoms identical to those described by Abbot and Ballantine for gobies (Gobius virescens). Using surface plasma resonance the sterol binding specificity of karlotoxins is shown to require desmethyl sterols. Our results with black lipid membranes indicate that karlotoxin forms large-conductance channels in the lipid membrane, which are characterized by large ionic conductance, poor ionic selectivity, and a complex gating behavior that exhibits strong voltage dependence and multiple gating patterns. In addition, we show that KmTx 2 pore formation is a highly targeted mechanism involving sterol-specificity. This is the first report of the functional properties of the membrane pores formed by karlotoxins and is consistent with the initial observations of Abbott and Ballantine from 1957.

A functional-group-based perspective on the response of marine phytoplankton to mesoscale eddies.

This study analyzed the response of marine phytoplankton to environmental changes induced by mesoscale warm eddies through the lens of functional groups, highlighting the complex interactions within the ecosystem. It was found that warm eddies significantly affected phytoplankton distribution, with cell abundance in the center being only 75.60 cells/L, compared to 1095.00 cells/L in the periphery. Vertical transport within warm eddies altered light conditions, affecting photophilic diatoms more, while increased temperatures favored the growth of warm-water dinoflagellates. This study also emphasized that ocean currents were significant factors, showing correlations with various functional groups and playing a key role in material transport and phytoplankton distribution. Additionally, the distinct responses of different functional groups to temperature and salinity underscored their unique adaptations to environmental changes. In periods without warm eddies, phytoplankton primarily congregated in shallower water layers.