Multi-species okadaic acid contamination and human poisoning during a massive bloom of Dinophysis acuminata complex in southern Brazil

Polystyrene microplastics exacerbated the toxicity of okadaic acid to the small intestine in mice

Microplastics (MPs) and okadaic acid (OA) are known to coexist in marine organisms, potentially impacting humans through food chain. However, the combined toxicity of OA and MPs remains unknown. In this study, mice were orally administered OA at 200 μg/kg bw and MPs at 2 mg/kg bw. The co-exposure group showed a significant increase in malondialdehyde (MDA) content and significant decreases in superoxide dismutase (SOD) activity and glutathione (GSH) level compared to the control, MPs and OA groups (p < 0.05). Additionally, the co-exposure group exhibited significantly higher levels of IL-1β and IL-18 compared to other groups (p < 0.05). These results demonstrated that co-exposure to MPs and OA induces oxidative stress and exacerbates inflammation. Histological and cellular ultrastructure analyses suggested that this combined exposure may enhance gut damage and compromise barrier integrity. Consequently, the concentration of OA in the small intestine of the co-exposure group was significantly higher than that in the OA group. Furthermore, MPs were observed in the lamina propria of the gut in the co-exposure group. Transcriptomic analysis revealed that the co-exposure led to increased expression of certain genes related to the NF-κB/NLRP3 pathway compared to the OA and MPs groups. Overall, this combined exposure may disrupt the intestinal barrier, and promote inflammation through the NF-κB/NLRP3 pathway. These findings provide precious information for the understanding of health risks associated with MPs and phycotoxins.

The Prevalence of Marine Lipophilic Phycotoxins Causes Potential Risks in a Tropical Small Island Developing State

Tropical small island developing states (SIDS), with their geographical isolation and limited resources, heavily rely on the fisheries industry for food and revenue. The presence of marine lipophilic phycotoxins (MLPs) poses risks to their economy and human health. To understand the contamination status and potential risks, the Republic of Kiribati was selected as the representative tropical SIDS and 55 species of 256 coral reef fish encompassing multiple trophic levels and feeding strategies were collected to analyze 17 typical MLPs. Our results showed that the potential risks of ciguatoxins were the highest and approximately 62% of fish species may pose risks for consumers. Biomagnification of ciguatoxins was observed in the food web with a trophic magnification factor of 2.90. Brevetoxin-3, okadaic acid, and dinophysistoxin-1 and -2 were first reported, but the risks posed by okadaic acid and dinophysistoxins were found to be negligible. The correlation analysis revealed that fish body size and trophic position are unreliable metrics to indicate the associated risks and prevent the consumption of contaminated fish. The potential risks of MLPs in Kiribati are of concern, and our findings can serve as valuable inputs for developing food safety policies and fisheries management strategies specific to tropical SIDS contexts.

Advances in the Early Warning of Shellfish Toxification by Dinophysis acuminata

In Western Europe, the incidence of DST is likely the highest globally, posing a significant threat with prolonged bans on shellfish harvesting, mainly caused by species of the dinoflagellate genus Dinophysis. Using a time series from 2014 to 2020, our study aimed (i) to determine the concentration of D. acuminata in water at which shellfish toxin levels could surpass the regulatory limit (160 µg OA equiv kg-1) and (ii) to assess the predictability of toxic events for timely mitigation actions, especially concerning potential harvesting bans. The analysis considered factors such as (i) overdispersion in the data, (ii) distinct periods of presence and absence, (iii) the persistence of cells, and (iv) the temporal lag between cells in the water and toxins in shellfish. Four generalized additive models were tested, with the Tweedie (TW-GAM) model showing superior performance (>85%) and lower complexity. The results suggest existing thresholds currently employed (200 and 500 cells L-1) are well-suited for the Portuguese coast, supported by empirical evidence (54-79% accuracy). The developed algorithm allows for thresholds to be tailored on a case-by-case basis, offering flexibility for regional variations.

Precautions for seafood consumers: An updated review of toxicity, bioaccumulation, and rapid detection methods of marine biotoxins

Seafood products are globally consumed, and there is an increasing demand for the quality and safety of these products among consumers. Some seafoods are easily contaminated by marine biotoxins in natural environments or cultured farming processes. When humans ingest different toxins accumulated in seafood, they may exhibit different poisoning symptoms. According to the investigations, marine toxins produced by harmful algal blooms and various other marine organisms mainly accumulate in the body organs such as liver and digestive tract of seafood animals. Several regions around the world have reported incidents of seafood poisoning by biotoxins, posing a threat to human health. Thus, most countries have legislated to specify the permissible levels of these biotoxins in seafood. Therefore, it is necessary for seafood producers and suppliers to conduct necessary testing of toxins in seafood before and after harvesting to prohibit excessive toxins containing seafood from entering the market, which therefore can reduce the occurrence of seafood poisoning incidents. In recent years, some technologies which can quickly, conveniently, and sensitively detect biological toxins in seafood, have been developed and validated, these technologies have the potential to help seafood producers, suppliers and regulatory authorities. This article reviews the seafood toxins sources and types, mechanism of action and bioaccumulation of marine toxins, as well as legislation and rapid detection technologies for biotoxins in seafood for official and fishermen supervision.

Red tides in the Galician rías: historical overview, ecological impact, and future monitoring strategies

The Galician rías (NW Iberia, Spain) are coastal embayments at the northern boundary of the Canary Current upwelling system. Their favourable conditions for phytoplankton growth turn them into a suitable area for the development of aquaculture activities and a site of most of the national shellfish production. Phytoplankton blooms, a natural phenomenon inside the rías, under certain conditions eventually lead to seawater discolourations (colloquially known as "red tides"). Because of their transient nature, available records derive mainly from opportunistic samplings or casual observations, and are scattered in the literature. As a rule of thumb, red tides in the NW Iberian Peninsula are of non-toxic nature and are not systematically monitored. However, in recent years striking exceptions such as those of the toxic dinoflagellate Alexandrium minutum, a producer of paralytic shellfish toxins, have been registered. The present study goes through a historical overview of red tides in the Galician rías, describing their colouring, responsible organisms, seasonal and geographical occurrence, and their association with other features (harmful algal blooms, biotoxins and shellfish harvesting closures, bioluminescence, etc.), ending with social challenges and proposals for improving the monitoring of red tides in the future.

Occurrence of potentially toxic microalgae and diarrhetic shellfish toxins in the digestive tracts of green sea turtles (Chelonia mydas) from southern Brazil

Algal toxins are involved in the mortality and/or illness of marine organisms via consumption of contaminated prey, or upon direct exposure to toxic cells. In this study, the presence of potentially toxic microalgal cells was investigated within the digestive tract contents of a threatened species of green turtle (Chelonia mydas). Additionally, lipophilic toxins were determined by LC-MS/MS in tissue samples (liver, stomach and/or intestine) of selected animals (n = 39 individuals) found dead-stranded in southern Brazil, from winter/2015 to autumn/2016. Thirteen potentially toxic species of microalgae (both benthic and planktonic), including seven dinoflagellates, six cyanobacteria and one diatom, were found in the digestive tract contents of green turtles. Among them, dinoflagellates belonging to the Dinophysis acuminata species complex were the most frequent (36%) and abundant (maximum average abundance of 566 cells g-1 in spring/2015). Moreover, 23% of the examined sea turtles exhibited detectable levels of the diarrhetic shellfish toxin okadaic acid (OA) in washed digestive tissues. Seven individuals accumulated OA in their intestines (max. 24.1 ng g-1) and two in the stomachs (max. 7.4 ng g-1). Toxin levels in the tissues were directly and significantly (r = 0.70, p < 0.025) associated with the cell abundance of OA-producing D. acuminata and Prorocentrum lima species complexes within the digestive contents of green turtles. Although OA concentrations were relatively low, possible chronic exposure might deteriorate general health conditions of exposed sea turtles, increasing the risk for diseases. Okadaic acid has been regarded as a tumor-promoting compound and an environmental co-factor in the incidence of fibropapillomatosis, a frequent disease in juvenile green turtles inhabiting this geographic region. Even though, only one green turtle containing OA in the digestive tissues (out of six examined) also presented fibropapillomatosis in this study. Notwithstanding, sea turtles are sentinels of ocean health. Monitoring the accumulation of algal toxins and their negative effects on these organisms contributes to conserving biodiversity and marine habitats.

Exposure to okadaic acid could disrupt the colonic microenvironment in rats

Okadaic acid (OA) is one of the most prevalent marine phycotoxin with complex toxicity, which can lead to toxic symptoms such as diarrhea, vomiting, nausea, abdominal pain, and gastrointestinal discomfort. Studies have shown that the main affected tissue of OA is digestive tract. However, its toxic mechanism is not yet fully understood. In this study, we investigated the changes that occurred in the epithelial microenvironment following OA exposure, including the epithelial barrier and gut bacteria. We found that impaired epithelial cell junctions, mucus layer destruction, cytoskeletal remodeling, and increased bacterial invasion occurred in colon of rats after OA exposure. At the same time, the gut bacteria decreased in the abundance of beneficial bacteria and increased in the abundance of pathogenic bacteria, and there was a significant negative correlation between the abundance of pathogenic bacteria represented by Escherichia/Shigella and animal body weight. Metagenomic analysis inferred that Escherichia coli and Shigella spp. in Escherichia/Shigella may be involved in the process of cytoskeletal remodeling and mucosal layer damage caused by OA. Although more evidence is needed, our results suggest that opportunistic pathogens may be involved in the complex toxicity of OA during OA-induced epithelial barrier damage.

Sample pooling and incurred samples improve analytical throughput and quality control of lipophilic phycotoxins screening in bivalve mollusks

Lipophilic marine biotoxins (LMBs) are one of the main risks associated with the consumption of mussels and oysters. Sanitary and analytical control programs are developed to detect the occurrence of these toxins in seafood before they reach toxic levels. To ensure quick results, methods must be easy and fast to perform. In this work, we demonstrated that incurred samples were a viable alternative to validation and internal quality control studies for the analysis of LMBs in bivalve mollusks. These samples were used to optimize, validate, and monitor a simple and fast ultrasound-assisted extraction (UAE) procedure. An internal quality control material containing okadaic acid (227 ± 46 µg kg-1) was produced and characterized. This material had its homogeneity and stability verified and was included as a quality control in all batches of analytical routine. Besides, a sample pooling protocol for extracts analysis was developed, based on tests for COVID-19. Up to 10 samples could be analyzed simultaneously, reducing the instrumental time of analysis by up to 80%. The UAE and sample pooling approaches were then applied to more than 450 samples, of which at least 100 were positive for the okadaic acid group of toxins.

Metabolites dynamics exacerbated by external nutrients inputs into a Ceratium hirundinella-dominated bloom in the Pengxi River, Three Gorges Reservoir, China

Secondary metabolites (toxins) production during harmful algal blooms (HABs) further increases the public health risks associated with water quality deterioration from anthropogenic eutrophication. In the present study, the dynamic pattern in the production of metabolites under different nutrient conditions in Ceratium-dominated spring HABs was investigated in Pengxi River, China. Results revealed five (5) important toxins all attributable to the Dinophyceae including azaspiracid 2&4, okadaic acid, tetrodotoxin, brevetoxin, and saxitoxin, each exhibiting certain levels of specificity to the ecosystem enrichments. In effect, while the production of azaspiracid 2 and okadaic acid was N-driven, azaspiracid 4 and tetrodotoxin were enhanced by Ca enrichment. The ambient HABs community structure shows absolute ecosystem dominance by a dinoflagellate, Ceratium hirundinella with relative abundance ((RA = 78.81%, p ˂ 0.05). However, P enrichment triggered a slight shift (p ≥ 0.05) in the HABs species structure within the cyanobacteria strictly represented by Chroococcus minor (RA = 26.60%) and Dolichospermum circinalis (RA = 23.91%) initiating possible emergency dominance. The effect of nutrient addition on biomass production as chlorophyll-a (Chl-a) confirmed a P-limited ecosystem juxtaposed by a secondary limitation by Ca. The significant stimulation on biomass as Chl-a from day 3 through day 4 by N and the multiple enrichments designated as NPFeCa was attributed to luxury consumption rather than limitation following N repletion thus delaying biomass accumulation. The study, therefore, offers useful insights into the dynamic pattern of toxins during spring HABs while it also provides comprehensive knowledge of the HABs impact predictions in the TGR.

Mortality and histopathology in sheepshead minnow (Cyprinodon variegatus) larvae exposed to pectenotoxin-2 and Dinophysis acuminata

Toxic species of the dinoflagellate genus Dinophysis can produce diarrheic toxins including okadaic acid (OA) and dinophysistoxins (DTXs), and the non-diarrheic pectenotoxins (PTXs). Okadaic acid and DTXs cause diarrheic shellfish poisoning (DSP) in human consumers, and also cause cytotoxic, immunotoxic and genotoxic effects in a variety of mollusks and fishes at different life stages in vitro. The possible effects of co-produced PTXs or live cells of Dinophysis to aquatic organisms, however, are less understood. Effects on an early life stage of sheepshead minnow (Cyprinodon variegatus), a common finfish in eastern USA estuaries, were evaluated using a 96-h toxicity bioassay. Three-week old larvae were exposed to PTX2 concentrations from 50 to 4000 nM, live Dinophysis acuminata culture (strain DAVA01), live cells resuspended in clean medium or culture filtrate. This D. acuminata strain produced mainly intracellular PTX2 (≈ 21 pg cell^-1), with much lower levels of OA and dinophysistoxin-1. No mortality or gill damages were observed in larvae exposed to D. acuminata (from 5 to 5500 cells mL^-1), resuspended cells and culture filtrate. However, exposure to purified PTX2 at intermediate to high concentrations (from 250 to 4000 nM) resulted in 8 to 100% mortality after 96 h (24-h LC₅₀ of 1231 nM). Histopathology and transmission electron microscopy of fish exposed to intermediate to high PTX2 concentrations revealed important gill damage, including intercellular edema, necrosis and sloughing of gill respiratory epithelia, and damage to the osmoregulatory epithelium, including hypertrophy, proliferation, redistribution and necrosis of chloride cells. Tissue damage in gills is likely caused by the interaction of PTX2 with the actin cytoskeleton of the affected gill epithelia. Overall, the severe gill pathology observed following the PTX2 exposure suggested death was due to loss of respiratory and osmoregulatory functions in C. variegatus larvae.

Phycotoxins and marine annelids - A global review

Several species of microalgae can produce potent phycotoxins that negatively affect aquatic organisms and their consumers following different exposure routes, as well as toxicokinetic (TK) and toxicodynamic (TD) processes. Benthic organisms are especially vulnerable as they are exposed to both benthic and planktonic species causative of harmful algal blooms (HABs). While benthic algae can come into direct contact with annelids during substrate remobilization, planktonic cells can settle to the bottom mostly during senescence and/or encystment stages, and in shallow and calm waters. We performed a systematic, qualitative review of the literature on the phycotoxin TK and TD processes in marine annelids, summarizing the most relevant findings and general trends. Besides, by using innovative analytical/statistical approaches, we were able to detect patterns and gaps in the current literature, thus pointing to future research directions. We retrieved and analyzed studies involving diarrhetic shellfish toxins (DSTs), paralytic shellfish toxins (PSTs), brevetoxins (PbTXs), domoic acid (DA), as well as palytoxin and its congeners, the ovatoxins (treated together as PLTXs). It is worth mentioning that studies evaluating other phycotoxins (e.g., ciguatoxins, yessotoxins) were not found in the literature. The absence of data on PbTXs, PSTs and DA is the largest gap hampering TK assessment in annelids, although some relevant information on TD is already available. Whereas lethal effects from DSTs have not been reported, more potent toxins like PbTXs, PSTs, DA and those grouped as PLTX-like compounds can cause mortality and/or marked decrease in annelid abundance. In addition, phycotoxins have been linked to sublethal effects on annelid cells. Although very sparse, field and laboratory studies offer strong evidence that annelids may be reliable indicators of toxin exposure and their negative effects during both early and later stages of HABs in marine environments. Besides quickly responding to these compounds at both organismic and suborganismic levels, annelids are easily found in areas affected by HABs. The use of annelids in future investigations evaluating the action mechanisms of toxic microalgae on marine invertebrates should be thus encouraged. In this case, the choice for widely dispersed and numerically dominant species of annelids would strengthen the validation and extrapolation of results from risk assessments in areas affected by HABs worldwide.

Cytotoxicity and intestinal permeability of phycotoxins assessed by the human Caco-2 cell model

Phycotoxins are a class of multiple natural metabolites produced by microalgae in marine and freshwater ecosystems that bioaccumulate in food webs, particularly in shellfish, having a great impact on human health. Phycotoxins are mainly leached and absorbed in the small intestine when human consumers accidentally ingest toxic aquatic products contaminated by them. To assess the intestinal uptake and damage of phycotoxins, a typical in vitro model was developed and widely applied using the human colorectal adenocarcinoma Caco-2 cell line. In this review, the application cases were summarized for multiple phycotoxins, including microcystins (MCs), cylindrospermopsins (CYNs), domoic acids (DAs), saxitoxins (STXs), palytoxins (PLTXs), okadaic acids (OAs), pectenotoxins (PTXs) and azaspiracids (AZAs). The results of the previous studies showed that each group of phycotoxins presented different cytotoxicity and mechanisms to Caco-2 cells, and significant discrepancies in the transport of phycotoxin across the Caco-2 cell monolayers. Therefore, this review describes the evaluation assays of the Caco-2 cell monolayer model, illustrates the principles of several primary cytotoxicity evaluation assays, and summarizes the cytotoxicity of each group of phycotoxins to Caco-2 cells line and their cellular transport, and finally proposes the development of multicellular intestinal models for future comprehensive studies on the toxicity and absorption of phycotoxins in the intestine. It will improve the understanding of Caco-2 cell monolayer models in the toxicology studies on phycotoxins and the potentially detrimental effects of microalgal toxins on the human intestine.

A simple method to evaluate the toxic effects of Prorocentrum lima extracts to fish (sea bass) kidney cells

The diarrhetic shellfish toxins (DSTs) okadaic acid (OA) and its analogues - the dinophysistoxins (DTXs) - are produced by dinoflagellates such as Prorocentrum lima and can bioaccumulate in filter-feeding organisms as they are transferred through the food web. Although there is no assessment of the harmful effects of these toxins on the fish's immune system, this study developed a primary culture protocol for kidney cells from marine fish Centropomus parallelus and evaluated the immunotoxic effects to P. lima extracts containing DSTs. The cells were obtained by mechanical dissociation, segregated with Percoll gradient, and incubated for 24 h at 28 °C in a Leibovitz culture medium supplemented with 2% fetal bovine serum and antibiotics. The exposed cells were evaluated in flow cytometry using the CD54 PE antibody. We obtained >5.0 × 10⁶ viable cells per 1.0 g of tissue that exhibited no cell differentiation. Exposure to 1.2 or 12 ng DST mL^-1 stimulated the immune system activation and increased the proportion of activated macrophages and monocytes in 48 to 52% and in 127 to 146%, respectively. The protocol proved to be an alternative tool to assess the immunotoxic effects of DST exposure on fish's anterior kidney cells.

Responses of JNK signaling pathway to the toxic dinoflagellate Prorocentrum lima in the mussel Perna viridis

Diarrheic shellfish poisoning (DSP) toxins are widely distributed over the world, causing diarrhea, vomiting, and even tumor in human. However, bivalves, the main carrier of the DSP toxins, have some tolerant mechanisms to DSP toxins, though it remains unclear. In this study, we scrutinized the role of Jun N-terminal kinases (JNK) in tolerance of DSP toxins and the relationship between JNK, apoptosis and nuclear factor E2-related factor/antioxidant response element (Nrf2/ARE) pathways. We found that the phosphorylated level of JNK protein was significantly increased both in hemocytes (6 h) and gills (3 h) of the mussel Perna viridis after short-term exposure to DSP toxins-producing dinoflagellate Prorocentrum lima. Exposure of P. lima induced oxidative stress in mussels. Hemocytes and gills displayed different sensitivities to the cytotoxicity of DSP toxins. Exposure of P. lima activated caspase-3 and induced apoptosis in gills but did not induce caspase-3 and apoptosis in hemocytes. The short-term exposure of P. lima could activate Nrf2/ARE signaling pathway in hemocytes (6 h), while longer-term exposure could induce glutathione reductase (GR) expression in hemocytes (96 h) and glutathione-S-transferases (GST) in gills (96 h). Based on the phylogenetic tree of Nrf2, Nrf2 in P. viridis was closely related to that in other mussels, especially Mytilus coruscus, but far from that in Mus musculus. The most likely phosphorylated site of Nrf2 in the mussels P. viridis is threonine 504 for JNK, which is different from that in M. musculus. Taken all together, the tolerant mechanism of P. viridis to DSP toxins might be involved in JNK and Nrf2/ARE signaling pathways, and JNK play a key role in the mechanism. Our findings provide a new clue to further understand tolerant mechanisms of bivalves to DSP toxins.

Prevalence of okadaic acid in benthic organisms associated Prorocentrum lima complex in a sub-tropical estuary

Lipophilic toxins were investigated in different benthic compartments of Paranaguá Bay, southern Brazil. Relatively low concentrations of okadaic acid (OA) were frequently reported in macrophyte extracts (maximum 0.64 ng g^-1), mainly in sheltered estuarine areas, correlated with the cell abundance of toxigenic benthic dinoflagellates, Prorocentrum lima. Non-conjugated OA was also detected in benthic marine animals, mostly during summer-autumn 2016. Higher OA concentrations were found in the viscera of Genidens genidens fish (24.3 ± 3.7 ng g^-1) and in soft tissues of Mytella guyanensis bivalves (21.3 ± 2.13 ng g^-1), whereas lower levels were less frequently reported in many other benthic feeders, including cephalopods, gastropods, crustaceans and fishes. Although OA concentrations were below the levels associated with acute human intoxication, possible chronic effects to benthic animals and their consumers cannot be disregarded due to the frequent presence of this biotoxin in various fishery resources. Human health risks are substantially enhanced for small-scale fishing communities and other socioeconomically vulnerable populations.

Antioxidant responses and okadaic acid accumulation in Laeonereis acuta (Annelida) exposed to the harmful dinoflagellate Prorocentrum cf. lima

We evaluated the accumulation of okadaic acid (OA), a diarrhetic toxin, and the antioxidant responses in the marine annelid Laeonereis acuta exposed to the benthic toxigenic dinoflagellate Prorocentrum cf. lima. Nontoxic Tetraselmis sp. was used as a control diet. Living cells of the two algae were supplied as food to animals kept in agar medium for 72 h. To assess the significance of the observed effects, our experimental design treated the algal species (diet), algal cell densities, and exposure time as fixed factors. Responses of the organisms were assessed through oxidative stress biomarkers (glutathione-S-transferase [GST], catalase [CAT], reduced glutathione [GSH] and lipid peroxidation [LPO]). Toxin accumulation was measured by LC-MS/MS in whole-body homogenates after 12, 24 and 72 h of exposure. Worms exposed to the toxigenic dinoflagellate gradually accumulated OA, with toxin levels directly related to the cell density of Prorocentrum cf. lima. Worms fed with Prorocentrum cf. lima exhibited decreased CAT activity, increased LPO levels - both interactively affected by algal species and time - and decreased GSH levels, which were interactively affected by algal species and cell density. Higher LPO levels, along with the inhibition of CAT and GSH, clearly indicated an oxidative stress situation in worms exposed to the toxigenic dinoflagellate. Laeonereis acuta accumulated moderate OA levels and may act as a vector of OA to food webs in estuarine areas under high Prorocentrum cf. lima abundance.

Harmful algal blooms and shellfish in the marine environment: an overview of the main molluscan responses, toxin dynamics, and risks for human health

Besides human health risks, phycotoxins may cause physiological injuries on molluscan shellfish and, consequently, damages to marine ecosystems and global fisheries production. In this way, this review aimed to present an overview of HABs impacts on marine shellfish by evaluating the effects of cultivated molluscs exposure to microalgae and cyanobacteria that form blooms and/or synthesize toxins. More specifically, it was assessed the main molluscan shellfish responses to harmful algae, trophic transfer and dynamics of phycotoxins, and the risks for human health. Of the 2420 results obtained from literature search, 150 scientific publications were selected after thorough inspections for subject adherence. In total, 70 molluscan species and 37 taxa of harmful algae were assessed from retrieved scientific publications. A significant positive correlation was found between the marine production of molluscs and the number of available studies by molluscan category. Molluscan responses to HABs and phycotoxins were categorized and discussed in three sub-sections: effects on grazing and behavior, metabolic and physiological reactions, and fitness consequences. The main histopathological injuries and toxin concentrations in molluscan tissues were also compiled and discussed. Bivalves often accumulate more toxins than gastropods and cephalopods, occasionally exceeding recommended levels for safe consumption, representing a risk for human health. Harmful algae impact on molluscan shellfish are complex to trace and predict; however, considering the perspective of increase in the occurrence and intensity of HABs, the intensification of efforts to expand the knowledge about HABs impacts on marine molluscs is crucial to mitigate the damages on economy and human health.

Occurrence and Trophodynamics of Marine Lipophilic Phycotoxins in a Subtropical Marine Food Web

Marine lipophilic phycotoxins (MLPs) are produced by toxigenic microalgae and cause foodborne illnesses. However, there is little information on the trophic transfer potential of MLPs in marine food webs. In this study, various food web components including 17 species of mollusks, crustaceans, and fishes were collected for an analysis of 17 representative MLPs, including azaspiracids (AZAs), brevetoxins (BTXs), gymnodimine (GYM), spirolides (SPXs), okadaic acid (OA), dinophysistoxins (DTXs), pectenotoxins (PTXs), yessotoxins (YTXs), and ciguatoxins (CTXs). Among the 17 target MLPs, 12, namely, AZAs1-3, BTX3, GYM, SPX1, OA, DTXs1-2, PTX2, YTX, and the YTX derivative homoYTX, were detected, and the total MLP concentrations ranged from 0.316 to 20.3 ng g^-1 wet weight (ww). The mean total MLP concentrations generally decreased as follows: mollusks (8.54 ng g^-1, ww) > crustaceans (1.38 ng g^-1, ww) > fishes (0.914 ng g^-1, ww). OA, DTXs, and YTXs were the predominant MLPs accumulated in the studied biota. Trophic dilution of the total MLPs was observed with a trophic magnification factor of 0.109. The studied MLPs might not pose health risks to residents who consume contaminated seafood; however, their potential risks to the ecosystem can be a cause for concern.

Effects of the toxic dinoflagellates Prorocentrum lima and Ostreopsis cf. ovata on immune responses of cultured oysters Crassostrea gasar

Oyster production in Brazil has been highlighted as an important economic activity and is directly impacted by the quality of the environment, which is largely the result of human interference and climate change. Harmful algal blooms occur in aquatic ecosystems worldwide, including coastal marine environments which have been increasing over the last decades as a result of global change and anthropogenic activities. In this study, the native oysters Crassostrea gasar from Northeast of Brazil were exposed to two toxic benthic dinoflagellate species, Prorocentrum lima and Ostreopsis cf. ovata. Their respective effects on C. gasar physiology and defense mechanisms were investigated. Oyster hemocytes were first exposed in vitro to different concentrations of both dinoflagellate species to assess their effects on hemocyte functions, such as phagocytosis, production of reactive oxygen species, as well as mortality. Results highlighted an alteration of hemocyte phagocytosis and viability in presence of O. cf. ovata, whereas P. lima did not affect the measured hemocyte functions. In a second experiment, oysters were exposed for 4 days in vivo to toxic culture of O. cf. ovata to assess its effects on hemocyte parameters, tissues damages and pathogenic Perkinsus spp. infection. An increase in hemocyte mortality was also observed in vivo, associated with a decrease of ROS production. Histopathological analyses demonstrated a thinning of the epithelium of the digestive tubules of the digestive gland, inflammatory reaction and a significant increase in the level of infection by Perkinsus spp. in oysters exposed to O. cf. ovata. These results indicate that oysters C. gasar seem to be pretty resilient to an exposure to P. lima and may be more susceptible to O. cf. ovata. Furthermore, the latter clearly impaired oyster physiology and defense mechanisms, thus highlighting that harmful algal blooms of O. cf. ovata could potentially lead to increased susceptibility of C. gasar oysters to parasite infections.

Multiscale physical background to an exceptional harmful algal bloom of Dinophysis acuta in a fjord system

Dinophysis acuta produces diarrhetic shellfish poisoning (DSP) toxins and pectenotoxins (PTX). It blooms in thermally-stratified shelf waters in late summer in temperate to cold temperate latitudes. Despite its major contribution to shellfish harvesting bans, little effort has been devoted to study its population dynamics in Chilean Patagonia. In 2017-2018, mesoscale distribution of harmful algal species (75 monitoring stations) revealed the initiation (late spring) and seasonal growth of a dense D. acuta population in the Aysén region, with maximal values at Puyuhuapi Fjord (PF). Vertical phytoplankton distribution and fine-resolution measurements of physical parameters along a 25-km transect in February 16^th identified a 15-km (horizontal extension) subsurface thin layer of D. acuta from 4 to 8 m depth. This layer, disrupted at the confluence of PF with the Magdalena Sound, peaked at the top of the pycnocline (6 m, 15.9 °C, 23.4 psu) where static stability was maximal. By February 22^nd, it deepened (8 m, 15.5 °C; 23.62 psu) following the excursions of the pycnocline and reached the highest density ever recorded (664 × 10³ cells L^-1) for this species. Dinophysis acuta was the dominant Dinophysis species in all microplankton net-tows/bottle samples; they all contained DSP toxins (OA, DTX-1) and PTX-2. Modeled flushing rates showed that Puyuhuapi, the only fjord in the area with 2 connections with the open sea, had the highest water residence time. Long term climate variability in the Southern hemisphere showed the effects of a Southern Annular Mode (SAM) in positive mode (+1.1 hPa) overwhelming a moderate La Niña. These effects included positive spring precipitation anomalies with enhanced salinity gradients and summer drought with positive anomalies in air (+1 °C) and sea surface (+2 °C) temperature. Locally, persistent thermal stratification in PF seemed to provide an optimal physical habitat for initiation and bloom development of D. acuta. Thus, in summer 2018, a favourable combination of meteorological and hydrographic processes of multiple scales created conditions that promoted the development of a widespread bloom of D. acuta with its epicentre at the head of Puyuhuapi fjord.

Potential applications of CRISPR/Cas for next-generation biomonitoring of harmful algae blooms: A review

Research on harmful algal and cyanobacterial blooms (HABs and CHABs) has risen dramatically due to their increasing global distribution, frequency, and intensity. These blooms jeopardize public health, ecosystem function, sustainability and can have negative economic impacts. Numerous monitoring programs have been established using light microscopy, liquid chromatography coupled to mass spectrometry (LC-MS), ELISA, and spectrophotometry to monitor HABs/CHABs outbreaks. Recently, DNA/RNA-based molecular methods have been integrated into these programs to replace or complement traditional methods through analyzing environmental DNA and RNA (eDNA/eRNA) with techniques such as quantitative polymerase chain reaction (qPCR), fluorescent in situ hybridization (FISH), sandwich hybridization assay (SHA), isothermal amplification methods, and microarrays. These have enabled the detection of rare or cryptic species, enhanced sample throughput, and reduced costs and the need for visual taxonomic expertise. However, these methods have limitations, such as the need for high capital investment in equipment or detection uncertainties, including determining whether organisms are viable. In this review, we discuss the potential of newly developed molecular diagnosis technology based on Clustered Regularly Interspaced Short Palindromic Repeats/Cas proteins (CRISPR/Cas), which utilizes the prokaryotic adaptative immune systems of bacteria and archaea. Cas12 and Cas13-based platforms can detect both DNA and RNA with attomolar sensitivity within an hour. CRISPR/Cas diagnostic is a rapid, inexpensive, specific, and ultrasensitive technology that, with some further development, will provide many new platforms that can be used for HABs/CHABs biomonitoring and research.

Marine invertebrate interactions with Harmful Algal Blooms - Implications for One Health

Harmful Algal Blooms (HAB) are natural atypical proliferations of micro or macro algae in either marine or freshwater environments which have significant impacts on human, animal and ecosystem health. The causative HAB organisms are primarily dinoflagellates and diatoms in marine and cyanobacteria within freshwater ecosystems. Several hundred species of HABs, most commonly marine dinoflagellates affect animal and ecosystem health either directly through physical, chemical or biological impacts on surrounding organisms or indirectly through production of algal toxins which transfer through lower-level trophic organisms to higher level predators. Traditionally, a major focus of HABs has concerned their natural production of toxins which bioaccumulate in filter-feeding invertebrates, which with subsequent trophic transfer and biomagnification cause issues throughout the food web, including the human health of seafood consumers. Whilst in many regions of the world, regulations, monitoring and risk management strategies help mitigate against the impacts from HAB/invertebrate toxins upon human health, there is ever-expanding evidence describing enormous impacts upon invertebrate health, as well as the health of higher trophic level organisms and marine ecosystems. This paper provides an overview of HABs and their relationships with aquatic invertebrates, together with a review of their combined impacts on animal, human and ecosystem health. With HAB/invertebrate outbreaks expected in some regions at higher frequency and intensity in the coming decades, we discuss the needs for new science, multi-disciplinary assessment and communication which will be essential for ensuring a continued increasing supply of aquaculture foodstuffs for further generations.

Toxin accumulation, detoxification and oxidative stress in bivalve (Anomalocardia flexuosa) exposed to the dinoflagellate Prorocentrum lima

Prorocentrum lima is a cosmopolitan benthic dinoflagellate capable of producing the diarrhetic shellfish toxins (DSTs) okadaic acid (OA) and dinophysistoxin (DTX). These compounds may cause oxidative stress and accumulate in bivalve tissues, which become vectors of intoxication to human consumers. We investigated DST accumulation, detoxification and oxidative stress biomarkers in clams (Anomalocardia flexuosa) experimentally exposed to P. lima cells or their compounds. Experimental diets consisted of 6000 cells mL-1 of the non-toxic chlorophyte Tetraselmis sp. (C; control condition), and combinations of C with 10 P. lima cells mL-1 (T10), 100 P. lima cells mL-1 (T100), or to a toxin concentration of ∼4 μg OA L-1 and ∼0.65 μg DTX-1 L-1 (T100d). Clams were exposed to these diets for 7 days (uptake phase), followed by a 7-day depuration period. No DSTs were detected in clams exposed to treatments C (control) nor to T100d (dissolved compounds) during either uptake or detoxification phase. Conversely, clams exposed to T10 or T100 accumulated, on average, up to 2.5 and 35 μg DST kg-1 in their whole bodies at the end of the uptake phase. These concentrations are ∼64 and ∼4.5 times lower than the regulatory level of 160 μg OA kg-1, respectively. Accumulated OA quotas were 12-22 times higher in the digestive gland (DG) than in remaining tissues over the uptake phase. Quick toxin transformation was indicated by the early detection of conjugated compounds - DTX-1 and OA esters - in the DG after 6 h of exposure, with OA-ester representing the main compound (30 - 100 %) in that tissue over the experiment. During the depuration period, detoxification rates represented 0.024 h-1, 0.04 h-1 and 0.052 h-1 for OA, DTX-1 and OA-ester, respectively. The activities of catalase, glutathione S-transferase, glutathione peroxidase and the levels of oxidative stress by lipoperoxidation varied similarly in the DG of A. flexuosa individuals subjected to T100, T100d and the control condition. However, contrasting antioxidant responses were measured in those exposed to T10. These findings indicate that no oxidative stress was primarily induced by DST-producing dinoflagellates in this clam species under laboratory conditions representative of toxic bloom situations. Even though, possible interactions should be considered under multistressor scenarios.

Response of fatty acids and lipid metabolism enzymes during accumulation, depuration and esterification of diarrhetic shellfish toxins in mussels (Mytilus galloprovincialis)

Bivalve mollusks accumulate diarrhetic shellfish toxins (DSTs) from toxigenic microalgae, thus posing a threat to human health by acting as a vector of toxins to consumers. In bivalves, free forms of DSTs can be esterified with fatty acids at the C-7 site to form acyl esters (DTX3), presumably a detoxification mechanism for bivalves. However, the effects of esterification of DSTs on fatty acid metabolism in mollusks remain poorly understood. In this study, mussels (Mytilus galloprovincialis) were fed the DST-producing dinoflagellate Prorocentrum lima for 10 days followed by an additional 10-days depuration in filtered seawater to track the variation in quantity and composition of DST acyl esters and fatty acids. A variety of esters of okadaic acid (OA) and dinophysistoxin-1 (DTX1) were mainly formed in the digestive gland (DG), although trace amounts of esters also appeared in muscle tissue. A large relative amount of OA (60%-84%) and DTX1 (80%-92%) was esterified to DTX3 in the visceral mass (referred to as digestive gland, DG), and the major ester acyl chains were C16:0, C16:1, C18:0, C18:1, C20:1 and C20:2. The DG and muscle tissues showed pronounced differences in fatty acid content and composition during both feeding and depuration periods. In the DG, fatty acid content gradually decreased in parallel with increasing accumulation and esterification of DSTs. The decline in fatty acids was accelerated during depuration without food. This reduction in the content of important polyunsaturated fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), would lead to a reduction in the nutritional value of mussels. Enzymes involved in lipid metabolism, including acetyl-coenzyme A carboxylase (ACC), fatty acid synthase (FAS), lipoprotein lipase (LPL) and hepatic lipase (HL), were actively involved in the metabolism of fatty acids in the DG, whereas their activities were weak in muscle tissue during the feeding period. This study helps to improve the understanding of interactions between the esterification of DSTs and fatty acid dynamics in bivalve mollusks.

Shellfish contamination with marine biotoxins in Portugal and spring tides: a dangerous health coincidence

Bivalve molluscs can acquire marine biotoxins by filter-feeding upon certain toxin-producing microalgae. The two most common syndromes observed in temperate coastal waters have been diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP). While DSP is a non-fatal gastrointestinal syndrome, PSP is a neurological syndrome which can lead to death by respiratory paralysis in high intoxication scenarios. In Portugal, the presence of both DSP and PSP toxins leads to recurrent seasonal bans of bivalve harvesting. On a few occasions, the bans were not placed in time, not properly disseminated to the public or were disregarded by recreational harvesters. Several cases of poisonings have been studied in collaboration between health authorities and the laboratory in charge of the biotoxin monitoring programme. Some of the outbreaks have even called the attention of the local media. In several of these recorded cases, a common trait has emerged throughout the years: bivalve harvest had often been done during very low tides attributed to either new or full moons. These tides expose intertidal bivalves more widely, increase harvesting time, and allow picking of larger-sized specimens. In some occasions, the consumers were extremely unfortunate because a noxious coincidence had occurred: larger-sized specimens were available but had attained the highest toxin content of the toxic season. This review alerts that despite costly monitoring programmes have been perfected through the years, human poisonings still take place due to the rapid increase in toxin levels and/or disrespect of harvest bans.

Evaluation of different strategies to minimize the matrix effects on LC-MS/MS analysis of multiple lipophilic shellfish toxins in both acidic and alkaline chromatographic conditions

Lipophilic shellfish toxins (LSTs) accumulated by shellfish pose a potential threat to consumer health. A mandatory routine monitoring of LSTs has been adopted for seafood products by liquid chromatography-mass spectrometry (LC-MS) in many countries. In this study, two methods developed on liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) under acidic and alkaline chromatographic conditions were assessed for the determination of multiple LSTs. Different strategies including matrix solid-phase dispersion (MSPD), solid phase extraction (SPE) and sample dilution were applied and evaluated the matrix effects of mussel, scallop, clam, and oyster samples on the signal response of mass spectrometry. Results showed that the alkaline method achieved a lower limit of detection (LOD) and more robust compared to the acidic method. The obvious signal suppression of OA and DTX1 (55%-76%) and signal enhancement of PTX2 (27%-34%) occurred in the crude extracts of shellfish under acidic chromatography. In the alkaline method, no remarkable matrix effects of crude extracts were found except for the scallop matrix on the signal intensity of DTX1, AZA3 and GYM-A (121%-130%). Clean-up methods MSPD, SPE and sample dilution obviously reduced the inhibition of shellfish matrices on the signal response of OA and DTX1, however, which were still subject to signal inhibition under acidic condition. Sample dilution was more effective than SPE and MSPD in minimizing the matrix interference in both acidic and alkaline methods. Furthermore, sample dilution in combination with the alkaline chromatography was the most effective method. Bivalve mollusks harvested from Beibu Bay, South China Sea, were generally contaminated by GYM-A and SPX1 at low concentrations.

Changes in colonic microbiotas in rat after long-term exposure to low dose of okadaic acid

Okadaic acid (OA), one of the most important phycotoxins, is widely distributed around the world, concerning diarrheic shellfish poisoning (DSP), and even colorectal cancer. Here, we found that long-term exposure of OA at a low dose (80 μg kg^-1 body weight) had certain effects on colonic microbiotas and tract in rat. In the OA-exposed rat, colonic epithelium layer was damaged, and relative abundance of some microbiotas were significantly changed, especially genera in Clostridiales. However, no intestinal inflammation or significant disease was observed. Combined with the increase in relative abundance of some genera in Clostridiales induced by OA in the fermentation experiment, we proposed that OA could cause damage to the intestinal epithelium and increase the relative abundance of pathogenic bacteria, thereby increasing the probability of contact between intestinal epithelium and pathogenic bacteria and leading to an easier pathogenicity.

Toxigenic phytoplankton groups and neurotoxin levels related to two contrasting environmental conditions at the coastal area of Rio de Janeiro (west of South Atlantic)

An assessment of the major pigments and neurotoxins and a description of the phytoplankton community were carried out within the coastal region of Rio de Janeiro State (Brazil), during winter and the following spring of 2018. Overall, six stations were investigated for oceanographic conditions (with CTD casts). Filtered water samples were used to estimate the chlorophyll a (CHL-a), carotenoids (CAR), and phycobiliproteins (PHY) using UV-Vis spectrophotometry, as well as the quantification of saxitoxins (STX) and domoic acid (DA), through High Performance Liquid Chromatography (HPLC). Planktonic organisms were counted using sedimentation chambers of different volumes and an inverted microscope. A cluster analysis, SIMPER, and ANOSIM were applied to the phytoplankton data along with diversity indexes, and non-parametric statistics to phycotoxins and pigments. There was a significant difference between the winter and spring phytoplankton community, associated with the mixed layer depth (r² = -0.626, p < 0.05) and temperature (r² = 0.641, p < 0.05). Phytoplankton biomass and C:CHL-a indicated a higher production during the winter than in spring, with the potentially toxic genus Pseudo-nitzschia responsible for 12.79% of autotrophic abundance (SIMPER output). Pigments showed a slight increase in CAR during spring, while PHY remained at trace concentrations. Both the DA and STX were quantified in winter and spring, but with significant differences only for STX between the sampling periods. Among the 71 taxa, 11 were identified as potentially toxic with an emphasis on STX-producing dinoflagellates and cyanobacteria, such as Alexandrium sp., Gymnodinium spp. along with Trichodesmium spp. Season-related environmental variability may be the major driving force modulating the mixed assemblage of species that support different levels of phycotoxins.