Phylogenetic analysis and yessotoxin profiles of Gonyaulax spinifera cultures from the Benguela Current upwelling system

Toxic effects of combined exposure to homoyessotoxin and nitrite on the survival, antioxidative responses, and apoptosis of the abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) and nitrite (NO2-N), released during harmful dinoflagellate cell lysis adversely affect abalones. However, their toxicity mechanisms in shellfish remain unclear. This study investigated the economic abalone species Haliotis discus hannai exposed to varying concentrations of homo-YTX (0, 2, 5, and 10 µg L-1) and NO2-N (0, 3, and 6 mg L-1) on the basis of their 12 h LC50 values (5.05 µg L-1 and 4.25 mg L-1, respectively) and the environmentally relevant dissolved concentrations during severe dinoflagellate blooms, including mixtures. The test abalones were exposed to homo-YTX and NO2-N for 12 h. The mortality rate (D), reactive oxygen species (ROS) levels, antioxidant defense capabilities, and expression levels of antioxidant-related, Hsp-related, and apoptosis-related genes in abalone gills were assessed. Results showed that the combined exposure to homo-YTX and NO2-N increased the D and ROS levels and upregulated B-cell lymphoma-2 (BCL2)-associated X (BAX) and caspase3 (CASP3) expression levels while reducing glutathione peroxidase (GPx) activity and GPx, CuZnSOD, and BCL2 expression levels. High concentrations of homo-YTX (10 µg L-1) and NO2-N (6 mg L-1) solutions and the combinations of these toxicants inhibited the activities of superoxide dismutase (SOD) and catalase (CAT) and downregulated the expression levels of MnSOD, CAT, Hsp70, and Hsp90. The ROS levels were negatively correlated with the activities of SOD, CAT, and GPx and the expression levels of MnSOD, CuZnSOD, CAT, GPx, Hsp70, Hsp90, and BCL2. These results suggest that homo-YTX, in conjunction with NO2-N, induces oxidative stress, disrupts antioxidant defense systems, and triggers caspase-dependent apoptosis in the gills of abalone. ROS-mediated antioxidative and heat-shock responses and apoptosis emerge as potential toxicity mechanisms affecting the survival of H. discus hannai due to homo-YTX and NO2-N exposure.

Effect of temperature on growth and yessotoxin production of Protoceratium reticulatum and Lingulodinium polyedra (Dinophyceae) isolates from the Portuguese coast (NE Atlantic)

The dinoflagellates Protoceratium reticulatum and Lingulodinium polyedra are potential yessotoxin (YTX) producers, which have been associated with blooms responsible for economic, social, and ecological impacts around the world. They occur in Iberian waters, but in this region, little is known of their ecophysiology and toxin profiles. This study investigated the growth and toxin production of two strains of each species, from the Portuguese coast, at 15 °C, 19 °C, and 23 °C. Growth curves showed higher growth rates at 19 °C, for both species. YTX and three analogs (homo YTX; 45-OH YTX; 45-OH homo YTX) were investigated by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS), and the presence of other analogs was investigated by Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS). No evidence of toxin production was found in L. polyedra. By contrast, YTX and 45,55-diOH-YTX were detected in both strains of P. reticulatum. These results confirm P. reticulatum as a source of yessotoxins along the Portuguese coast and add to the observed high intraspecific variability on YTX production of both species, at a global scale.

ROS-mediated physiological activities and apoptotic effect on the survival of abalone (Haliotis discus hannai) under homoyessotoxin and ammonia stresses

Serious dinoflagellate blooms produce homoyessotoxin (homo-YTX) and ammonia (NH3-N) in eutrophic seawaters, posing threats to the healthy development of the mariculture industry. This study aimed to explore the toxicity mechanism of homo-YTX and NH3-N on the survival of abalone, which is important for the ecotoxicological research and cultivation of shellfish. The economy abalone Haliotis discus hannai was placed in homo-YTX (0, 2, 5, and 10 μg L-1) and NH3-N (0, 1.08, and 3.16 mg L-1) and a mixture of the two compounds to determine the survival rate (S), antioxidative responses, physiological activities, and apoptosis of abalone. Results show that the combination of homo-YTX and NH3-N increased the reactive oxygen species level, the malondialdehyde content, and the expression level of BCL2-associated X but decreased S; the activities of superoxide dismutase, catalase, adenosine triphosphatase, glutamic-pyruvic transaminase, xanthine oxidase, lactate dehydrogenase, and lysozyme; and the expression level of B-cell lymphoma-2. The activities of alkaline phosphatase and acid phosphatase in 10 μg L-1 of homo-YTX and 3.16 mg L-1 of NH3-N solutions and in the mixture of the two toxicants decreased. The caspase3 expression level was downregulated in 10 μg L-1 of homo-YTX. These results suggest that homo-YTX and NH3-N enhanced the oxidative stress and lipid peroxidation reactions, inhibited the energy supply, disrupted the metabolic and immune physiological functions, and activated apoptosis in the gills of abalone. ROS-mediated physiological activities and apoptosis were among the potential toxicity mechanisms of the interactive effects of homo-YTX and NH3-N on abalone.

Occurrence and distribution of lipophilic marine algal toxins in the coastal seawater of Southeast China and the South China Sea

The composition, levels, and spatial distribution of dissolved lipophilic marine algal toxins (LMATs) including cyclic imines (CIs), yessotoxins (YTXs), okadaic acid (OA) and its derivatives, pectenotoxins (PTXs), azaspiracids (AZAs), and brevetoxins (BTXs) in the coastal waters of Southeast China (Xiamen) and the South China Sea (Hainan Island and Beibu Gulf) were investigated and compared for the first time. Dissolved AZA3 was firstly detected in the coastal seawater of China. OA and PTX2 were widely distributed in the three areas studied. Gymnodimine (GYM), 13-desmethyl spirolide C (SPX1), YTX, and homo-yessotoxins (h-YTX) were found mainly in the South China Sea. The average ∑LMAT concentrations in the coastal waters of Xiamen, Hainan Island, and Beibu Gulf were 10.02 ng/L, 4.21 ng/L, and 44.27 ng/L, respectively. More groups and much higher concentrations of LMATs occurred in the South China Sea than that in the other sea areas of China.

Metabarcoding of harmful algal bloom species in sediments from four coastal areas of the southeast China

In the past three decades, harmful algal blooms (HAB) have become more frequent and widespread in southeast Chinese sea areas. Resting stages are regarded as the “seed bank” of algal blooms, and play an important role in initiating HABs. The distribution of resting stages in sediments especially those of HAB species can make good predictions about the potential risk of future blooms, however with limited reports. In this study, surface sediment samples were collected in the four sea areas along the southeast Chinese coasts, including Dafeng Port (DF) in the southern Yellow Sea, Xiangshan Bay (XS), Funing Bay (FN), and Dongshan Bay (DS) in the East China Sea. Diversity and community structure of eukaryotic microalgae in surface sediments were assessed by metabarcoding V4 region of the 18S rDNA, focusing on the distribution of HAB species. Biogenic elements including total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), biogenic silicon (BSi), and moisture content (MC) were analyzed. A total of 454 eukaryotic algal OTUs were detected, which belonged to 31 classes of 9 phyla. Altogether 149 algal species were detected in this study, and 59 taxa have been reported to form resting stages. Eukaryotic algal community was similar in XS, FN and DS of the East China Sea, which were predominated by dinoflagellates. However, algal community was different in DF of the Yellow Sea, and characterized by the dominance of chrysophytes and low OTU richness. The distribution of most abundant HAB species showed positive correlations with TN, BSi, and TOC, suggesting that eutrophication and consequent increase in diatom productivity may have a significant influence on the distribution of HAB species and facilitate the occurrence of HABs. Furthermore, HAB species occurred more abundantly and widely in FN. Our results suggest high potential risks of HABs in the southeast Chinese coast especially in Funing Bay.

Changes in physiological activities are responsible for homoyessotoxin-induced toxicity in abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) is a lipid-soluble toxin produced by toxic dinoflagellates. It is widely distributed in marine ecosystems worldwide, and it poses a threat to the survival of aquatic animals. The tissues of the abalone Haliotis discus hannai are easily damaged by homo-YTX during harmful algal blooms. In this study, H. discus hannai was exposed to homo-YTX (0, 2, 5, and 10 µg L^-1) to evaluate the rates of survival (S) and death (D) and the antioxidative, metabolic, and digestive physiological responses in the gills and digestive gland of abalone. Homo-YTX decreased S and the activities of Na⁺/K⁺-adenosine triphosphatase, Ca²⁺/Mg²⁺-adenosine triphosphatase, superoxide dismutase, catalase, alkaline phosphatase, xanthine oxidase, lactate dehydrogenase, amylase, protease, and lipase. Meanwhile, D, the reactive oxygen species level, and the malondialdehyde content increased with increasing concentrations of homo-YTX. In addition, homo-YTX induced oxidative stress, enhanced the lipid peroxidation reaction, reduced the energy supply, and inhibited the metabolic and digestive physiological activities in the gills and digestive gland of abalone. Oxidative stress-mediated insufficient energy supply and physiological activity reduction caused the death of abalone.

Unraveling the Gonyaulax baltica Species Complex: Cyst-theca Relationship of Impagidinium variaseptum, Spiniferites pseudodelicatus sp. nov. and S. ristingensis (Gonyaulacaceae, Dinophyceae), With Descriptions of Gonyaulax bohaiensis sp. nov, G. amoyensis sp. nov. and G. portimonensis sp. nov

The taxonomy of the extant dinoflagellate genus Gonyaulax is challenging since its thecate morphology is rather conservative. In contrast, cysts of Gonyaulax are varied in morphology and have been related with the fossil-based genera Spiniferites and Impagidinium. To better understand the systematics of Gonyaulax species, we performed germination experiments on cysts that can be identified as S. ristingensis, an unidentified Spiniferites with petaloid processes here described as Spiniferites pseudodelicatus sp. nov. and Impagidinium variaseptum from Chinese and Portuguese waters. Despite marked differences in cyst morphology, motile cells of S. pseudodelicatus and I. variaseptum are indistinguishable from Gonyaulax baltica. Motile cells hatched from S. ristingensis are morphologically similar to G. baltica as well but differ in the presence of one pronounced antapical spine. Three new species, Gonyaulax amoyensis (cyst equivalent S. pseudodelicatus), Gonyaulax bohaiensis (cyst equivalent I. variaseptum), and Gonyaulax portimonensis (cyst equivalent S. ristingensis), were erected. In addition, a new ribotype (B) of G. baltica was reported from South Korea and a bloom of G. baltica ribotype B is reported from New Zealand. Molecular phylogeny based on LSU and SSU rRNA gene sequences revealed that Gonyaulax species with minute or short antapical spines formed a well-resolved clade, whereas species with two pronounced antapical spines or lack of antapical spines formed the sister clade. Six strains of four above species were examined for yessotoxin production by liquid chromatography coupled with tandem mass spectrometry, and very low concentrations of yessotoxin were detected for one G. bohaiensis strain.

Spatial distribution and source of biotoxins in phytoplankton from the South China Sea, China

Marine phycotoxins severely threaten ecosystem health and mariculture. This study investigates the spatial distribution and source of diverse phycotoxins in the South China Sea (SCS), during four 2019/2020 cruises. Saxitoxin (STX) and okadaic acid (OA) -groups, azaspiracids, cyclic imines, pectenotoxins (PTX), yessotoxins, and domoic acid (DA) toxins were analyzed in microalgal samples. PTX2 occurred with the highest (93.5%) detection rate (DR) during all cruises, especially in the Pearl River Estuary (PRE) in June 2019. Homo-yessotoxin (hYTX) and DA were found during three cruises in August 2020, and high DR of hYTX (67.7%, 29.3%) and DA (29.0%, 29.3%) in the PRE and Guangdong coast, respectively, in June 2019 and 2020, peaking at concentrations of 777 pg hYTX L^-1 and 38514 pg DA L^-1. The phycotoxin distribution demonstrated that DA-producing microalgae gathered close to the PRE and Guangdong coast, while hYTX-producing microalgae distributed relatively far offshore. Microalgae producing PTX2- and STX-group toxins were more widely living in the SCS. High-throughput sequencing results suggested that Alexandrium pacificum and Gonyaulax spinifera were responsible for STX-group toxins and hYTX, respectively, while Pseudo-nitzschia cuspidata was the main source of DA. Widely distributed PTX2, hYTX, and DA were reported for the first time in the SCS.

New Trends in the Occurrence of Yessotoxins in the Northwestern Adriatic Sea

Yessotoxins (YTXs) are polycyclic toxic ether compounds produced by phytoplanktonic dinoflagellates which accumulate in filter-feeding organisms. We know that the water temperature in our areas Northwestern Adriatic Sea is optimal for the growth of potentially toxic algae (around 20 °C). In recent years, these temperatures have remained at these levels for longer and longer periods, probably due to global warming, which has led to an excessive increase in toxin levels. The interruption of mussel harvesting caused by algae negatively affects farmers’ revenues and the availability of local fish, causing a major economic loss in Italy’s main shellfish sector. Methods: In the nine years considered, 3359 samples were examined: 1715 marine waters, 73 common clams; 732 mussels; 66 oysters; and 773 veracious clams. Bivalve molluscs were examined for the presence of marine biotoxins, including YTXs, while potentially toxic algae, including those producing YTXs, were searched for and counted in marine waters. The method adopted for the quantification of lipophilic toxins involves the use of an LC-MS/MS system. The enumeration of phytoplankton cells was performed according to the Utermhöl method. Results: Between 2012 and 2020, 706 molluscs were tested for YTXs. In total, 246 samples tested positive, i.e., 34.84%. Of the positive samples, 30 exceeded the legal limit. Conclusion: In this regard, it is essential to develop and activate, as soon as possible, an “early warning” system that allows a better control of the production areas of live bivalve molluscs, thus allowing an optimal management of the plants in these critical situations.

Distribution and diversity of eukaryotic microalgae in Kuwait waters assessed using 18S rRNA gene sequencing

The microbial communities play a crucial role in ecosystem functioning through interactions among individuals and taxonomic groups in a highly dynamic marine ecosystem. The structure and functioning of the microbial communities are often influenced by the changes in the surrounding environment. Monitoring the microbial diversity of the marine ecosystem helps to understand spatial patterns of microbial community and changes due to season, climate, and various drivers of biological diversity. Kuwait is characterized by an arid environment with a high degree of temperature variation during summer and winter. Our understanding of spatial distribution patterns of microbial communities, their diversity, and the influence of human activities on the degree of changes in the diversity of the microbial community in Kuwait territorial waters remain unclear. In this study, we employed 18S rRNA sequencing to explore marine microalgal community composition and dynamics in seawater samples collected from Kuwait waters over two seasonal cycles across six locations. A total of 448,184 sequences across 36 replicates corresponding to 12 samples from six stations were obtained. The quality-filtered sequences were clustered into 1,293 representative sequences, which were then classified into different eukaryotic taxa. This study reveals that the phytoplankton community in Kuwait waters is diverse and shows significant variations among different taxa during summer and winter. Dinoflagellates and diatoms were the most abundant season-dependent microalgae taxa in Kuwait waters. Alexandrium and Pyrophacus were abundant in summer, whereas Gonyaulax was abundant during the winter. The abundance of Coscinodiscus and Navicula, of the diatom genera, were also dependent upon both seasonal and possible anthropogenic factors. Our results demonstrate the effectiveness of a sequencing-based approach, which could be used to improve the accuracy of quantitative eukaryotic microbial community profiles.

Harmful algal blooms of the Benguela eastern boundary upwelling system

The Benguela Upwelling System (BUS) is subject to a high incidence of HABs. Of the major shellfish poisoning syndromes associated with HABs, Paralytic and Diarrhetic Shellfish Poisoning (PSP and DSP) pose the greatest concern, but as documented herein there are several other HAB organisms that are also present. Blooms of Alexandrium catenella have been recognised as the typical cause of PSP since 1948. In addition to the risk posed to human health A. catenella has also been the cause of large shellfish and bird mortalities. An additional risk of PSP is provided by Alexandrium minutum first detected in Cape Town harbour in 2003. DSP was identified on the South African coast for the first time in 1991. Although several Dinophysis spp. known to cause DSP have been recognized as a component of the plankton of the region, it is accepted that DSP is usually attributed to D. acuminata or D. fortii. In the southern Benguela both Pseudo-nitzschia australis and Pseudo-nitzschia multiseries have been identified and shown to produce domoic acid. Multiple Pseudo-nitzschia spp. have been identified in the northern Benguela with the potentially toxigenic Pseudo-nitzschia pungens and P. australis dominant inshore. The yessotoxin (YTX) producing dinoflagellates Gonyaulax spinifera, Lingulodinium polyedrum and Protoceratium reticulatum are all known to form blooms and YTXs have been the cause of massive mortalities of farmed abalone. Prominent fish-killing blooms include Karlodinium veneficum in the northern Benguela and Karenia cristata in the southern Benguela. Shellfish farms in an embayment of the southern Benguela have suffered reduced growth rates due to the ecosystem disruptive blooms of Aureococcus anophagefferens. High biomass dinoflagellate blooms often attributed to Tripos and Prorocentrum spp. characterise the entire region and major mortalities of marine life are regularly attributed to their decay and the subsequent development of anoxic conditions.