Domoic acid accumulation in French shellfish in relation to toxic species of Pseudo-nitzschia multiseries and P. pseudodelicatissima

Spatiotemporal variations of domoic acid: New findings in the sedimentary environment of a typical nearshore mariculture bay, China

Domoic acid (DA) is a neurotoxin produced by marine microalgae. It tends to accumulate in marine shellfish and fish, posing a threat to aquaculture and seafood consumers' health. In this study, DA in the surface and bottom seawater, sediment, and porewater of the Jiaozhou Bay, a typical mariculture bay in China, was systematically investigated for the first time over different seasons. Surprisingly, a high concentration of DA was discovered in the marine sediment porewater (maximum detected concentration: 289.49 ng/L) for the first time. DA was found to be extensively distributed in the water body and sedimentary environment of the Jiaozhou Bay. DA in the surface and bottom seawater of Jiaozhou Bay in spring was uniformly distributed, whereas DA showed obvious spatial variations in summer and winter. The high concentration areas of DA are located in the north of Jiaozhou Bay and decreased to the south areas. DA was also distributed in the sediment (spring mean: 316.57 ng/kg; summer mean: 10.22 ng/kg; winter mean: 237.08 ng/kg) and porewater (spring mean: 129.70 ng/L; summer mean: 53.54 ng/L; winter mean: 19.90 ng/L) of Jiaozhou Bay. The DA concentrations in the surface sediment and porewater were higher in the spring than in the winter and summer, contrary to the seasonal variation pattern observed in the surface and bottom seawater. The DA concentration in porewater was significantly higher than in the surface and bottom seawater, indicating that the risk of pollution contamination from DA to benthic fishery organisms may be underestimated. Overall, DA is widely distributed in the seawater and also in the benthic environment of Jiaozhou Bay and exhibited potential harm to fishery organisms varied greatly with seasons. It is an important discovery for marine algae toxins and has important guiding significance and important indicative role for the routine monitoring and management of DA pollution in water and benthic environment.

The queen scallop Aequipecten opercularis: A slow domoic acid depurator?

Domoic acid (DA) is a dangerous phycotoxin produced by several strains of diatoms of the genus Pseudo-nitzschia, and responsible for Amnesic Shellfish Poisoning (ASP) in humans. The increasingly intense ASP-outbreaks along the English Channel over the last three decades have forced persistent harvest closures of economically important and highly contaminated bivalve stocks exhibiting slow DA-depuration rates, like the king scallop Pecten maximus. Under this scenario, other pectinid species, such as the queen scallop Aequipecten opercularis have been empirically proposed as alternative resources to redress the high economic losses due to the banning of the exploitation of P. maximus. Nevertheless, the kinetics of DA depuration in A. opercularis have not been assessed so far, and its direct extraction after ASP-episodes could represent a serious threat to public health. Hence, the main objective of this work was to estimate the DA-depuration rate in the digestive gland (DG) of naturally contaminated scallops A. opercularis after a toxic Pseudo-nitzschia australis bloom subjected to experimental depuration in the laboratory for 30 days. This study also intended to go further in the knowledge about the anatomical distribution of DA in scallop tissues, and corroborate the implications of autophagy in DA-sequestration in the DG of this species as recently hypothesized. In the DG, the DA-depuration rate (0.018 day-1) suggested that even with toxin burdens as low as 40 mg⋅kg-1 in the DG, queen scallops may remain contaminated for about 70 days, thus longer under intensely contamination scenarios. The subcellular analyses corroborated DA-sequestration mainly through late-autophagy within residual bodies in the DG, without differences in the frequencies of anti-DA labeled residual bodies across the entire depuration process. These results revealed that A. opercularis cannot be considered a fast DA-depurator, and represent a baseline knowledge for decision-making about harvesting natural beds of queen scallops after toxic Pseudo-nitzschia blooms. The findings of this work also represent a cornerstone for further research to accelerate DA-depuration in this species.

The amnesic shellfish poisoning toxin, domoic acid: The tattoo of the king scallop Pecten maximus

Domoic acid (DA) is a potent neurotoxin produced by diatoms of the genus Pseudo-nitzschia and is responsible for Amnesic Shellfish Poisoning (ASP) in humans. Some fishery resources of high commercial value, such as the king scallop Pecten maximus, are frequently exposed to toxic Pseudo-nitzschia blooms and are capable of accumulating high amounts of DA, retaining it for months or even a few years. This poses a serious threat to public health and a continuous economical risk due to fishing closures of this resource in the affected areas. Recently, it was hypothesized that trapping of DA within autophagosomic-vesicles could be one reason explaining the long retention of the remaining toxin in P. maximus digestive gland. To test this idea, we follow the kinetics of the subcellular localization of DA in the digestive glands of P. maximus during (a) the contamination process - with sequential samplings of scallops reared in the field during 234 days and naturally exposed to blooms of DA-producing Pseudo-nitzschia australis, and (b) the decontamination process - where highly contaminated scallops were collected after a natural bloom of toxic P. australis and subjected to DA-depuration in the laboratory for 60 days. In the digestive gland, DA-depuration rate (0.001 day-1) was much slower than contamination kinetics. The subcellular analyses revealed a direct implication of early autophagy in DA sequestration throughout contamination (r = 0.8, P < 0.05), while the presence of DA-labeled residual bodies (late autophagy) appeared to be strongly and significantly related to slow DA-depuration (r = -0.5) resembling an analogous DA-tattooing in the digestive glands of P. maximus. This work provides new evidence about the potential physiological mechanisms involved in the long retention of DA in P. maximus and represents the baseline to explore procedures to accelerate decontamination in this species.

Marine phycotoxin levels in shellfish-14 years of data gathered along the Italian coast

Along the Italian coasts, toxins of algal origin in wild and cultivated shellfish have been reported since the 1970s. In this study, we used data gathered by the Veterinary Public Health Institutes (IZS) and the Italian Environmental Health Protection Agencies (ARPA) from 2006 to 2019 to investigate toxicity events along the Italian coasts and relate them to the distribution of potentially toxic species. Among the detected toxins (OA and analogs, YTXs, PTXs, STXs, DAs, AZAs), OA and YTX were those most frequently reported. Levels exceeding regulatory limits in the case of OA (≤2,448 μg equivalent kg-1) were associated with high abundances of Dinophysis spp., and in the case of YTXs (≤22 mg equivalent kg-1) with blooms of Gonyaulax spinifera, Lingulodinium polyedra, and Protoceratium reticulatum. Seasonal blooms of Pseudo-nitzschia spp. occur all along the Italian coast, but DA has only occasionally been detected in shellfish at concentrations always below the regulatory limit (≤18 mg kg-1). Alexandrium spp. were recorded in several areas, although STXs (≤13,782 µg equivalent kg-1) rarely and only in few sites exceeded the regulatory limit in shellfish. Azadinium spp. have been sporadically recorded, and AZAs have been sometimes detected but always in low concentrations (≤7 µg equivalent kg-1). Among the emerging toxins, PLTX-like toxins (≤971 μg kg-1 OVTX-a) have often been detected mainly in wild mussels and sea urchins from rocky shores due to the presence of Ostreopsis cf. ovata. Overall, Italian coastal waters harbour a high number of potentially toxic species, with a few HAB hotspots mainly related to DSP toxins. Nevertheless, rare cases of intoxications have occurred so far, reflecting the whole Mediterranean Sea conditions.

Comparative study of domoic acid accumulation, isomer content and associated digestive subcellular processes in five marine invertebrate species

Despite the deleterious effects of the phycotoxin domoic acid (DA) on human health, and the permanent threat of blooms of the toxic Pseudo-nitzschia sp. over commercially important fishery-resources, knowledge regarding the physiological mechanisms behind the profound differences in accumulation and depuration of this toxin in contaminated invertebrates remain very scarce. In this work, a comparative analysis of accumulation, isomer content, and subcellular localization of DA in different invertebrate species was performed. Samples of scallops Pecten maximus and Aequipecten opercularis, clams Donax trunculus, slippersnails Crepidula fornicata, and seasquirts Asterocarpa sp. were collected after blooms of the same concentration of toxic Pseudo-nitzschia australis. Differences (P < 0.05) in DA accumulation were found, wherein P. maximus showed up to 20-fold more DA in the digestive gland than the other species. Similar profiles of DA isomers were found between P. maximus and A. opercularis, whereas C. fornicata was the species with the highest biotransformation rate (∼10 %) and D. trunculus the lowest (∼4 %). DA localization by immunohistochemical analysis revealed differences (P < 0.05) between species: in P. maximus, DA was detected mainly within autophagosome-like vesicles in the cytoplasm of digestive cells, while in A. opercularis and C. fornicata significant DA immunoreactivity was found in post-autophagy residual bodies. A slight DA staining was found free within the cytoplasm of the digestive cells of D. trunculus and Asterocarpa sp. The Principal Component Analysis revealed similarities between pectinids, and a clear distinction of the rest of the species based on their capabilities to accumulate, biotransform, and distribute the toxin within their tissues. These findings contribute to improve the understanding of the inter-specific differences concerning the contamination-decontamination kinetics and the fate of DA in invertebrate species.

Emerging phylogeographic perspective on the toxigenic diatom genus Pseudo-nitzschia in coastal northern European waters and gateways to eastern Arctic seas: Causes, ecological consequences and socio-economic impacts

The diatom Pseudo-nitzschia H. Peragallo is perhaps the most intensively researched genus of marine pennate diatoms, with respect to species diversity, life history strategies, toxigenicity, and biogeographical distribution. The global magnitude and consequences of harmful algal blooms (HABs) of Pseudo-nitzschia are particularly significant because of the high socioeconomic impacts and environmental and human health risks associated with the production of the neurotoxin domoic acid (DA) among populations of many (although not all) species. This has led to enhanced monitoring and mitigation strategies for toxigenic Pseudo-nitzschia blooms and their toxins in recent years. Nevertheless, human adaptive actions based on future scenarios of bloom dynamics and proposed shifts in biogeographical distribution under climate-change regimes have not been implemented on a regional scale. In the CoCliME (Co-development of climate services for adaptation to changing marine ecosystems) program these issues were addressed with respect to past, current and anticipated future status of key HAB genera such as Pseudo-nitzschia and expected benefits of enhanced monitoring. Data on the distribution and frequency of Pseudo-nitzschia blooms in relation to DA occurrence and associated amnesic shellfish toxin (AST) events were evaluated in a contemporary and historical context over the past several decades from key northern CoCliME Case Study areas. The regional studies comprised the greater North Sea and adjacent Kattegat-Skagerrak and Norwegian Sea, eastern North Atlantic marginal seas and Arctic gateways, and the Baltic Sea. The first evidence of possible biogeographical expansion of Pseudo-nitzschia taxa into frontier eastern Arctic gateways was provided from DNA barcoding signatures. Key climate change indicators, such as salinity, temperature, and water-column stratification were identified as drivers of upwelling and advection related to the distribution of regional Pseudo-nitzschia blooms. The possible influence of changing variables on bloom dynamics, magnitude, frequency and spatial and temporal distribution were interpreted in the context of regional ocean climate models. These climate change indicators may play key roles in selecting for the occurrence and diversity of Pseudo-nitzschia species within the broader microeukaryote communities. Shifts to higher temperature and lower salinity regimes predicted for the southern North Sea indicate the potential for high-magnitude Pseudo-nitzschia blooms, currently absent from this area. Ecological and socioeconomic impacts of Pseudo-nitzschia blooms are evaluated with reference to effects on fisheries and mariculture resources and coastal ecosystem function. Where feasible, effective adaptation strategies are proposed herein as emerging climate services for the northern CoCLiME region.

Progresses of the Influencing Factors and Detection Methods of Domoic Acid

Domoic acid (DA) is a neurotoxin mainly produced by Pseudo-nitzschia diatom, which belongs to the genera Rhomboida. It can combine with the receptors of glutamate of neurotransmitters, then affecting the normal nerve signal transmission of the organism and causing nervous system disorders. However, as a natural marine drug, DA can also be used for pest prevention and control. Although the distribution of DA in the world has already been reported in the previous reviews, the time and location of its first discovery and the specific information are not complete. Therefore, the review systematically summarizes the first reported situation of DA in various countries (including species, discovery time, and collection location). Furthermore, we update and analyze the factors affecting DA production, including phytoplankton species, growth stages, bacteria, nutrient availability, trace metals, and so on. These factors may indirectly affect the growth environment or directly affect the physiological activities of the cells, then affect the production of DA. Given that DA is widely distributed in the environment, we summarize the main technical methods for the determination of DA, such as bioassay, high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA), biosensor, and so on, as well as the advantages and disadvantages of each method used so far, which adds more new knowledge in the literature about DA until now. Finally, the DA research forecast and its industrial applications were prospected to prevent its harm and fully explore its potential value.

Residue Analysis and Assessment of the Risk of Dietary Exposure to Domoic Acid in Shellfish from the Coastal Areas of China

Harmful algal blooms in Chinese waters have caused serious domoic acid (DA) contamination in shellfish. Although shellfish are at particular risk of dietary exposure to DA, there have been no systematic DA risk assessments in Chinese coastal waters. A total of 451 shellfish samples were collected from March to November 2020. The presence of DA and four of its isomers were detected using liquid chromatography-tandem mass spectrometry. The spatial-temporal distribution of DA occurrence and its potential health risks were examined. DA was detected in 198 shellfish samples (43.90%), with a maximum level of 942.86 μg/kg. DA was recorded in all 14 shellfish species tested and Pacific oysters (Crassostrea gigas) showed the highest average DA concentration (82.36 μg/kg). The DA concentrations in shellfish showed distinct spatial-temporal variations, with significantly higher levels of occurrence in autumn than in summer and spring (p < 0.01), and particularly high occurrence in Guangdong and Fujian Provinces. The detection rates and maximum concentrations of the four DA isomers were low. While C. gigas from Guangdong Province in September showed the highest levels of DA contamination, the risk to human consumers was low. This study improves our understanding of the potential risk of shellfish exposure to DA-residues.

Development of harmful algal blooms species responsible for lipophilic and amnesic shellfish poisoning intoxications in southwestern Mediterranean coastal waters

Mediterranean waters have undergone environmental changes during the last decades leading to various modifications of the structure of phytoplankton populations, especially Harmful Algal Blooms (HABs) species. Monitoring of the potentially toxic phytoplankton species was carried out biweekly in the western Mediterranean coast of Morocco from March 2018 to March 2019. Lipophilic Shellfish Toxins (LSTs) using LC-MS/MS and Domoic Acid (DA) using HPLC-UV were measured in the exploited mollusks, the cockle Acanthocardia tuberculata and the smooth clam Callista chione. We also determined the prevailing environmental factors in four surveyed sites (M'diq bay, Martil, Kaa Asras, and Djawn) selected to cover a variety of coastal ecosystems. Results showed that Pseudo-nitzschia spp. a DA producer species, was abundant with a pick of 50 × 10³ cells l^-1 on October 2018 in Djawn. Dinophysis caudata was the dominate Dinophysis species and showed a maximum density of 2200 cells l^-1 on July in Djawn. Prorocentrum lima, an epibenthic dinoflagellate, appeared rarely in the water column with densities <80 cells l^-1. Gonyaulax spinifera and Protoceratium reticulatum were found occasionally with a maximum density of 160 cells l^-1. Karenia selliformis was detected only five times (<80 cells l^-1) throughout the survey period. LC-MS/MS analyses revealed the presence of OA/DTX3, PTX-2, PTX-2 sa, and PTX-2 sa epi in the cockle at concentrations of up to 44.81 (OA/DTX-3+PTXs) ng g^-1 meat. GYM-A was detected in the clam at concentrations of up to 4.22 ng g^-1 meat. For the first time, AZAs and YTXs were detected in the southwestern Mediterranean with maximum values of 2.49 and 10.93 ng g^-1 meat of cockle, respectively. DA was detected in moderate concentrations not exceeding 5.65 μg g^-1 in both mollusks. Results showed that the observed toxic algae in the water column were responsible from the analysed toxins in the mollusks. It is likely that the southwestern Mediterranean waters could see the development of emergent species producing potent toxins (YTXs, AZAs, GYM-A). These dinoflagellates have to be isolated, ribotyped, and their toxin profiles determined.

Human poisonings by neurotoxic phycotoxins related to the consumption of shellfish: study of cases registered by the French Poison Control Centres from 2012 to 2019

CONTEXT

In June 2019, a paralytic shellfish poisoning (PSP) case related to the consumption of mussels contaminated by saxitoxins at a concentration below the regulatory threshold came to the attention of the French Agency for Food, Environmental and Occupational Health and Safety (ANSES). This pointed to probable undetected human cases of poisoning by neurotoxic phycotoxins.

METHODS

We conducted a retrospective study of poisoning cases by bivalve shellfish (oysters, mussels and scallops) recorded by the French Poison Control Centres (PCC) from 2012 to 2019. All medical records were reviewed by a toxicologist.Cases that could be related to neurotoxic phycotoxins were selected and described. Diagnosis was based on symptoms compatible with ingestion of contaminated shellfish and on contamination data for the shellfish production area (analysed by the French Research Institute for Exploitation of the Sea, Ifremer), or notifications to the European Rapid Alert System for Food and Feed when the origin of the shellfish was known.

RESULTS

Among the 619 shellfish poisoning cases recorded by the PCCs from 2012 to 2019, 22% (n = 134) had reported at least one neurological symptom (headache, dizziness or paraesthesia). Review of medical records for the 134 patients led to suspicion of 14 cases of PSP and one case of amnesic shellfish poisoning. Five patients experienced persistent neurological symptoms. Marine toxins were not tested for in the blood or urine of these patients.

CONCLUSION

This retrospective identification of cases strongly suspected of being related to neurotoxic phycotoxins led ANSES, PCCs and Ifremer to develop a specific questionnaire and to recommend actions to take when neurological symptoms related to shellfish consumption are reported to a PCC. Daily monitoring of shellfish poisoning cases registered in the national PCCs database was also implemented in order to rapidly detect any suspicious cases, alert the competent authorities, and warn the general population.

Occurrence and Seasonal Monitoring of Domoic Acid in Three Shellfish Species from the Northern Adriatic Sea

As filter feeders, bivalves and ascidians can accumulate contaminants present in the environment and pass them on to higher food chain levels as vectors. The consumption of bivalves contaminated with the potent neurotoxin domoic acid (DA) can cause amnesic shellfish poisoning in humans. The aim of this study was to determine seasonal differences in occurrence and accumulation of this phycotoxin in European oysters (Ostrea edulis Linnaeus, 1758) (n = 46), Queen scallops (Aequipecten opercularis Linnaeus, 1758) (n = 53), and edible ascidians of the Microcosmus spp. (n = 107), originating from the same harvesting area in the Northern Adriatic Sea. The quantification was performed using ultra-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) preceded by derivatization with dansyl chloride. DA was found in very low concentrations throughout the year, with a maximum value of 810 μg/kg in Queen scallops. This study reveals differences in the occurrence and accumulation of DA between Queen scallops and the other two investigated species (oysters and ascidians) and the highest concentrations during the colder part of the year. Even though DA was detected in all of them, Queen scallops showed higher DA accumulation compared to the other two (p < 0.001), hence representing a sentinel species suitable for the monitoring of DA level in seafood.

Rapid electrochemical detection of domoic acid based on polydopamine/reduced graphene oxide coupled with in-situ imprinted polyacrylamide

Domoic acid, namely amnesic shellfish toxin, is a highly neurotoxic substance to marine animals and humankind. To reduce the incidence of poisoning accidents, the exploitation of specific and rapid detection method for domoic acid monitoring is highly required. Herein, an electrochemical molecularly imprinted polymer (MIP) sensor based on polydopamine-reduced graphene oxide/polyacrylamide composite (PDA-rGO/PAM) was constructed successfully to detect domoic acid. The domoic acid molecule could be recognized in imprinted cavities of PAM reversibly through hydrogen bonding. PDA-rGO promoted the loading capacity of PAM and improved the charge transfer rate, which amplified the electrical signal response of the MIP sensor. The screen-printed electrode (SPE) modified with PDA-rGO/PAM displayed satisfactory response toward toxin contaminated sample at a linear range from 1 to 600 nM and a low detection limit of 0.31 nM, demonstrating the prospective application of the transducer as a portable sensing platform for the on-site detection of hazardous marine biotoxin. Moreover, benefiting from the superior specificity and stability of MIP, the fabricated sensor could be utilized to detect the domoic acid content in mussel extracts directly without complex pretreatment operation.

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.

Interactions between Filter-Feeding Bivalves and Toxic Diatoms: Influence on the Feeding Behavior of Crassostrea gigas and Pecten maximus and on Toxin Production by Pseudo-nitzschia

Among Pseudo-nitzschia species, some produce the neurotoxin domoic acid (DA), a source of serious health problems for marine organisms. Filter-feeding organisms—e.g., bivalves feeding on toxigenic Pseudo-nitzschia spp.—are the main vector of DA in humans. However, little is known about the interactions between bivalves and Pseudo-nitzschia. In this study, we examined the interactions between two juvenile bivalve species—oyster (Crassostrea gigas) and scallop (Pecten maximus)—and two toxic Pseudo-nitzschia species—P. australis and P. fraudulenta. We characterized the influence of (1) diet composition and the Pseudo-nitzschia DA content on the feeding rates of oysters and scallops, and (2) the presence of bivalves on Pseudo-nitzschia toxin production. Both bivalve species fed on P. australis and P. fraudulenta. However, they preferentially filtered the non-toxic Isochrysis galbana compared to Pseudo-nitzschia. The presence of the most toxic P. australis species resulted in a decreased clearance rate in C. gigas. The two bivalve species accumulated DA in their tissues (up to 0.35 × 10⁻³ and 5.1 × 10⁻³ µg g⁻¹ for C. gigas and P. maximus, respectively). Most importantly, the presence of bivalves induced an increase in the cellular DA contents of both Pseudo-nitzschia species (up to 58-fold in P. fraudulenta in the presence of C. gigas). This is the first evidence of DA production by Pseudo-nitzschia species stimulated in the presence of filter-feeding bivalves. The results of this study highlight complex interactions that can influence toxin production by Pseudo-nitzschia and accumulation in bivalves. These results will help to better understand the biotic factors that drive DA production by Pseudo-nitzschia and bivalve contamination during Pseudo-nitzschia blooms.

Long Term Memory Outcome of Repetitive, Low-Level Dietary Exposure to Domoic Acid in Native Americans

Domoic acid (DA) is a marine-based neurotoxin that, if ingested via tainted shellfish, is associated with Amnesic Shellfish Poisoning (ASP). These acute effects of elevated DA exposure in humans have been well described. In contrast, the long-term impacts of lower level, repetitive, presumably safe doses of DA (less than 20 ppm) are minimally known. Since Native Americans (NA) residing in coastal communities of the Pacific NW United States are particularly vulnerable to DA exposure, this study focuses on the long-term, 8-year memory outcome associated with their repeated dietary consumption of the neurotoxin. Measures of razor clam consumption, memory, clerical speed and accuracy, and depression were administered over eight years to 500 randomly selected adult NA men and women ages 18–64. Data were analyzed using GEE analyses taking into consideration the year of study, demographic factors, and instrumentation in examining the association between dietary exposure and outcomes. Findings indicated a significant but small decline in total recall memory within the context of otherwise stable clerical speed and accuracy and depression scores. There is reason to believe that a continuum of memory difficulties may be associated with DA exposure, rather than a unitary ASP syndrome.

RNA Viruses in Aquatic Unicellular Eukaryotes

Increasing sequence information indicates that RNA viruses constitute a major fraction of marine virus assemblages. However, only 12 RNA virus species have been described, infecting known host species of marine single-celled eukaryotes. Eight of these use diatoms as hosts, while four are resident in dinoflagellate, raphidophyte, thraustochytrid, or prasinophyte species. Most of these belong to the order Picornavirales, while two are divergent and fall into the families Alvernaviridae and Reoviridae. However, a very recent study has suggested that there is extraordinary diversity in aquatic RNA viromes, describing thousands of viruses, many of which likely use protist hosts. Thus, RNA viruses are expected to play a major ecological role for marine unicellular eukaryotic hosts. In this review, we describe in detail what has to date been discovered concerning viruses with RNA genomes that infect aquatic unicellular eukaryotes.

Occurrence of domoic acid and cyclic imines in marine biota from Lebanon-Eastern Mediterranean Sea

Marine biotoxins are naturally existing chemicals produced by toxic algae and can accumulate in marine biota. When consumed with seafood, these phycotoxins can cause human intoxication with symptoms varying from barely-noticed illness to death depending on the type of toxin and its concentration. Recently, the occurrence of marine biotoxins has been given special attention in the Mediterranean as it increased in frequency and severity due to anthropogenic pressures and climate change. Up to our knowledge, no previous study reported the presence of lipophilic toxins (LTs) and cyclic imines (CIs) in marine biota in Lebanon. Hence, this study reports LTs and CIs in marine organisms: one gastropod (Phorcus turbinatus), two bivalves (Spondylus spinosus and Patella rustica complex) and one fish species (Siganus rivulatus), collected from various Lebanese coastal areas. The results show values below the limit of detection (LOD) for okadaic acid, dinophysistoxin-1 and 2, pectenotoxin-1 and 2, yessotoxins, azaspiracids and saxitoxins. The spiny oyster (S. spinosus) showed the highest levels of domoic acid (DA; 3.88 mg kg^-1), gymnodimine (GYM-B) and spirolide (SPX) (102.9 and 15.07 μg kg^-1, respectively) in congruence with the occurrence of high abundance of Pseudo-nitzchia spp., Gymnodinium spp., and Alexandrium spp. DA levels were below the European Union (EU) regulatory limit, but higher than the Lowest Observed Adverse Effect Level (0.9 μg g^-1) for neurotoxicity in humans and lower than the Acute Reference Dose (30 μg kg^-1 bw) both set by the European Food Safety Authority (EFSA, 2009). Based on these findings, it is unlikely that a health risk exists due to the exposure to these toxins through seafood consumption in Lebanon. Despite this fact, the chronic toxicity of DA, GYMs and SPXs remains unclear and the effect of the repetitive consumption of contaminated seafood needs to be more investigated.

Toxic marine microalgae and noxious blooms in the Mediterranean Sea: A contribution to the Global HAB Status Report

We review the spatial distribution of toxic marine microalgal species and the impacts of all types of harmful algal events (Harmful Algal Blooms, HABs) in the Mediterranean Sea (MS), including the Black Sea, the Sea of Marmara, coastal lagoons and transitional waters, based on two databases compiled in the Ocean Biogeographic Information System (OBIS). Eighty-four potentially toxic species have been detected in the MS (2,350 records), of which 16 described from these waters between 1860 and 2014 and a few suspected to have been introduced. More than half of these species (46) produce toxins that may affect human health, the remainders ichthyotoxic substances (29) or other types of toxins (9). Nevertheless, toxicity-related events are not frequent in the MS (308 records in 31 years), and mainly consist of impacts on aquaculture, caused by the dinoflagellates Dinophysis and Alexandrium, along with a few actual shellfish poisoning cases. Pseudo-nitzschia blooms are widespread, but domoic acid in shellfish rarely exceeds regulatory levels. Fish kills are probably less sporadic than reported, representing a problem at a few places along the southern MS coasts and in the Ebro River Delta. Since the last decade of the 20^th century, blooms of the benthic dinoflagellates Ostreopsis cf. ovata have regularly occurred all along rocky shores of the MS, at times with human health problems caused by toxic aerosol. New records of Gambierdiscus and Fukuyoa, until now reported for the westernmost and easternmost MS coasts, raise concerns about the risk of ciguatera, a syndrome so far known only for subtropical and tropical areas. Recent discoveries are the dinoflagellates Vulcanodinium rugosum, responsible for the presence of pinnatoxins in French lagoons' shellfish, and the azaspiracid-producers Azadinium spp. Mucilages and discolorations have a major impact on tourism in summer. Reports of toxic species and HABs have apparently increased in the MS over the last half century, which is likely related to the increased awareness and monitoring operations rather than to an actual increase of these phenomena. Indeed, while the case of Ostreopsis appears as a sudden upsurge rather than a trend, no actual increase of toxic or noxious events has so far emerged in intensively studied areas, such as the French and Spanish coasts or the Adriatic Sea. Moreover, some cases of decrease are reported, e.g., for Alexandrium minutum blooms disappearing from the Harbour of Alexandria. Overall, main HAB risks derive from cases of massive development of microalgal biomass and consequent impacts of reduced coastal water quality on tourism, which represents the largest part of the marine economy along the MS coasts.

Occurence and Variability of Domoic Acid in Mussel (Mytilus galloprovincialis) Samples from the Golden Horn Estuary, Sea of Marmara (Turkey)

The occurrence and variability of domoic acid (DA) levels in wild Mytilus galloprovincialis samples, compared with the Pseudo-nitzschia spp. abundance and particulate DA (pDA) concentrations in relation to the environmental changes in the Golden Horn Estuary, Turkey from October 2018 to September 2019. Biotoxin analysis were performed by high-performance liquid chromatography with diode-array detection (HPLC-DAD). DA concentrations in particulate matter (pDA) and mussel samples were found between 0.090-0.685 µg L^-1 and 0.905-2.413 µg g^-1, respectively. Accumulation of DA in wild mussel samples could be the result of the increasing tendency of P.nitzschia spp. abundances between April and May. Maximum DA levels were detected in particulate matter when the salinity was measured as the lowest in May. Thus, it can be said that the DA production was driven by the significant salinity decrease in the GHE. This is the first attempt regarding the presence of DA in M. galloprovincialis samples collected from Turkish coasts.

Three decades of data on phytoplankton and phycotoxins on the French coast: Lessons from REPHY and REPHYTOX

In France, REPHY (Observation and Surveillance Network for Phytoplankton and Hydrology in coastal waters) and REPHYTOX (Monitoring Network for Phycotoxins in marine organisms) have been contributing to long-term time series on ocean health for more than 30 years. The aim of this paper is to describe these networks and to highlight their key results. Over the last 20 years, phytoplankton flora analysis on French coasts from the Channel to Mediterranean has shown that the five "emblematic" taxa are Chaetoceros, Skeletonema, Cryptophyceae, Leptocylindrus and Pseudo-nitzschia. The latter, together with the taxa of interest Dinophysis + Phalacroma, Alexandrium, and Karenia, have been consistently recorded along the entire French coastline. However, when taking into account frequency of occurrence some taxa exhibit more distinct geographical distributions. In particular, the occurrence of Phaeocystis appeared to be strongly specific to the northern coasts of the Channel. French coasts have been regularly affected since the 1980s by the presence of toxins in bivalve molluscs, leading to bans on fishing and sale of shellfish during periods of varying duration. Three categories of toxins were involved. PST and AST were absent from the French coasts, respectively before 1988 and 2000. DST (Diarrheic Shellfish Toxins) have affected many areas along the whole coast every year since 1987. For PST (Paralytic Shellfish Toxins), only a few areas have been affected, sometimes sporadically, since 1988 in the Channel, 1993 in the Atlantic, and 1998 in the Mediterranean. Many areas have been impacted since 2000 by AST (Amnesic Shellfish Toxins) episodes, mainly affecting scallops in the Channel and on Atlantic coasts. The patterns of change of shellfish toxicity episodes showed no real trend in any province over the entire period 1987-2018.

Diversity and regional distribution of harmful algal events along the Atlantic margin of Europe

The IOC-ICES-PICES Harmful Algal Event Database (HAEDAT) was used to describe the diversity and spatiotemporal distribution of harmful algal events along the Atlantic margin of Europe from 1987 - 2018. The majority of events recorded are caused by Diarrhetic Shellfish Toxins (DSTs). These events are recorded annually over a wide geographic area from southern Spain to northern Scotland and Iceland, and are responsible for annual closures of many shellfish harvesting areas. The dominant causative dinoflagellates, members of the morphospecies 'Dinophysis acuminata complex' and D. acuta, are common in the waters of the majority of countries affected. There are regional differences in the causative species associated with PST events; the coasts of Spain and Portugal with the dinoflagellates Alexandrium minutum and Gymnodinium catenatum, north west France/south west England/south Ireland with A. minutum, and Scotland/Faroe Islands/Iceland with A. catenella. This can influence the duration and spatial scale of PST events as well as the toxicity of shellfish. The diatom Pseudo-nitzschia australis is the most widespread Domoic Acid (DA) producer, with records coming from Spain, Portugal, France, Ireland and the UK. Amnesic Shellfish Toxins (ASTs) have caused prolonged closures for the scallop fishing industry due to the slow depuration rate of DA. Amendments to EU shellfish hygiene regulations introduced between 2002 and 2005 facilitated end-product testing and sale of adductor muscle. This reduced the impact of ASTs on the scallop fishing industry and thus the number of recorded HAEDAT events. Azaspiracids (AZAs) are the most recent toxin group responsible for events to be characterised in the ICES area. Events associated with AZAs have a discrete distribution with the majority recorded along the west coast of Ireland. Ciguatera Poisoning (CP) has been an emerging issue in the Canary Islands and Madeira since 2004. The majority of aquaculture and wild fish mortality events are associated with blooms of the dinoflagellate Karenia mikimotoi and raphidophyte Heterosigma akashiwo. Such fish killing events occur infrequently yet can cause significant mortalities. Interannual variability was observed in the annual number of HAEDAT areas with events associated with individual shellfish toxin groups. HABs represent a continued risk for the aquaculture industry along the Atlantic margin of Europe and should be accounted for when considering expansion of the industry or operational shifts to offshore areas.

Dose-response assessment for impaired memory from chronic exposure to domoic acid among native American consumers of razor clams

Domoic acid (DA) is a marine neurotoxin that accumulates in filtering shellfish during harmful algal blooms. A health protection limit of 20 ppm DA in razor clams (RC) has been set based principally upon an episode of acute DA toxicity in humans that included Amnesic Shellfish Poisoning among survivors. The objective of this study was to determine the dose-response relationship between estimated DA exposure through RC consumption and memory loss in Washington state Native Americans from 2005 to 2015. Results from total learning recall (TLR) memory scores were compared before and after the highest DA exposures. A decrease in TLR was related to DA dose (p < 0.01) regardless whether the effect was assumed to be transient or lasting, and whether the dose was expressed as an average daily dose or an average dose per meal. Benchmark dose modeling identified BMDL₁₀ values of 167 ng/kg-day and 2740 ng/kg-meal assuming a transient effect, and 196 ng/kg-day and 2980 ng/kg-meal assuming no recovery of function occurs. These DA dose thresholds for a measurable memory function reduction observed in this study of clam consumers are well below the safe acute dose underpinning the current regulatory DA limit of 20 ppm (ca. 60 μg/kg).

Distribution of Domoic Acid in the Digestive Gland of the King Scallop Pecten maximus

The king scallop Pecten maximus retains the amnesic shellfish poisoning toxin, domoic acid (DA), for a long time. Most of the toxin is accumulated in the digestive gland, but this organ contains several cell types whose contribution to the accumulation of the toxin is unknown. Determining the time-course of the depuration by analyzing whole organs is difficult because the inter-individual variability is high. A sampling method, using biopsies of the digestive gland, has been developed. This method allows for repetitive sampling of the same scallop, but the representativeness of the samples obtained in this way needs to be validated. In this work, we found that the distribution of DA in the digestive gland of the scallops is mostly homogeneous. Only the area closest to the gonad, and especially its outer portion, had a lower concentration than the other ones, probably due to a transfer of the toxin to the intestinal loop. Samples obtained by biopsies can therefore be considered to be representative. Most of the toxin was accumulated in large cells (mostly digestive cells), which could be due to differences during the toxin absorption or to the preferential depuration of the toxin from the small cells (mostly secretory).

Managing the Agri-Food System of Watersheds to Combat Coastal Eutrophication: A Land-to-Sea Modelling Approach to the French Coastal English Channel

The continental coastal waters of the Eastern Channel, from Normandy to Hauts-de-France, are subject to the major influence of unbalanced nutrient inputs from inflowing rivers. Several episodes of harmful algal blooms (HABs) compromising fishing and shellfish farming activities have been observed at the coast. For a better understanding of how the land-to-sea aquatic continuum functions, the GRAFS-RIVERSTRAHLER river biogeochemical model was implemented to cover the watersheds of 11 rivers flowing into this area (including the Seine) and chained with the ecological marine ECO-MARS3D model, applied to the French Northern coastal zone. Human activities strongly impact on the functioning of coastal ecosystems. Specifically, for these fertile soils of Northern France, intensive agricultural nitrogen (N) deliveries in excess over silica (Si) and phosphorus (P), essentially of diffuse origin, are potentially responsible for coastal eutrophication. Phosphorous is today equally supplied by diffuse and point sources, after a drastic reduction of inputs from wastewater treatment plants since the 2000s, and is better balanced regarding Si, as shown by the indicators of coastal eutrophication potential (P-ICEP versus N-ICEP). However, despite this drastic P reduction, HABs still appear repeatedly. Exploration of several scenarios of agro-food chain reorganization shows that (i) further progress in urban wastewater treatment to fully comply with current European regulations will not result in a significant reduction of nutrient fluxes to the sea, hence including HABs, and (ii) radical structural changes in agriculture, based on generalization of long and diversified organic crop rotations, reconnection of crop and livestock farming and changes in the human diet have the capacity to significantly reduce nutrient flows, coastal eutrophication and HABs.

Risk assessment for ballast water management - Learning from the Adriatic Sea case study

The ballast water management convention incorporates principles of risk assessment. A new ballast water management risk assessment model was developed to support the implementation of most efficient management measures, which we also present as a flowchart decision support system model. The risk assessment model was tested using data from port baseline surveys where available, and real shipping and ballast water discharges data. The here presented ballast water management risk assessment and possible management options are applicable elsewhere to support and improve complex decision making in the implementation of management requirements according to the ballast water management convention. If needed, the model may easy be adapted to address local specifics in any other region or area.

Influence of sudden salinity variation on the physiology and domoic acid production by two strains of Pseudo-nitzschia australis

Several coastal countries including France have experienced serious and increasing problems related to Pseudo-nitzschia toxic blooms. These toxic blooms occur in estuarine and coastal waters potentially subject to fluctuations in salinity. In this study, we document for the first time the viability, growth, photosynthetic efficiency, and toxin production of two strains of Pseudo-nitzschia australis grown under conditions with sudden salinity changes. Following salinity variation, the two strains survived over a restricted salinity range of 30-35, with favorable physiological responses, as the growth, effective quantum yield and toxin content were high compared to the other conditions. In addition, high cellular quotas of domoic acid (DA) were observed at a salinity of 40 for the strain IFR-PAU-16.1 in comparison with the other strain IFR-PAU-16.2 where the cell DA content was directly released into the medium. On the other hand, the osmotic stress imposed at lower salinities, 20 and 10, resulted in cell lysis and a sudden DA leakage in the medium. Intra-specific variability was observed in growth and toxin production, with the strain IFR-PAU-16.1 apparently able to withstand higher salinities than the strain IFR-PAU-16.2. On the whole, DA does not appear to act as an osmolyte in response to sudden salinity changes. Since most of the shellfish harvesting areas of bivalve molluscs in France are located in areas where the salinity generally varies between 30 and 35, Pseudo-nitzschia australis blooms might potentially impact public health and commercial shellfish resources in these places.

Insights into the harmful algal flora in northwestern Mediterranean coastal lagoons revealed by pyrosequencing metabarcodes of the 28S rRNA gene

This study investigated the genetic diversity of phytoplankton communities in six shallow lagoons located on the French coast of the northwestern Mediterranean Sea that represented a trophic gradient ranging from oligotrophic to hypereutrophic. The phytoplankton communities were sampled once a month from spring (May) to the beginning of autumn (September/early October) in 2012 and fractionated by size. Metabarcodes were generated from cDNAs by targeting the D1-D2 region of the 28S rRNA gene and pyrosequenced using Roche 454 technology. Examination of the annotated barcodes revealed harmful algal species not previously documented in these lagoons. Three ichthyotoxic species belonging to Pfiesteriaceae were detected: Luciella masanensis was relatively widespread and abundant in many samples, whereas Pfiesteria piscicida and Stoeckeria changwonensis were found as single barcode sequences. Furthermore, a phylogenetic analysis of barcodes annotated as belonging to Pfiesteriaceae suggested the existence of two previously undescribed clades. The other toxic or potentially harmful dinoflagellates detected through rare barcodes were Dinophysis acuminata, Vulcanodinium rugosum, Alexandrium andersonii and A. ostenfeldii. The two most abundant dinoflagellate taxa were Gymnodinium litoralis and Akashiwo sanguinea with respect to sequence numbers. Four diatom species from the genus Pseudo-nitzschia that potentially produce domoic acid were identified (P. galaxiae, P. delicatissima, P. brasiliana and P. calliantha). These observations are discussed in terms of the literature and monitoring records related to the identified taxa in this Mediterranean area.

Two decades of Pseudo-nitzschia spp. blooms and king scallop (Pecten maximus) contamination by domoic acid along the French Atlantic and English Channel coasts: Seasonal dynamics, spatial heterogeneity and interannual variability

King scallop contamination (Pecten maximus) by domoic acid, a neurotoxin produced by some species of the diatom Pseudo-nitzschia, is highly problematic because of its lengthy retention in the bivalve tissue, leading to prolonged fishery closures. Data collected within the French Phytoplankton and Phycotoxin monitoring network (REPHY) over the 1995-2012 period were used to characterize the seasonal dynamics and the interannual variability of P.-nitzschia spp. blooms as well as the contamination of king scallop fishing grounds, in six contrasted bays distributed along the French Atlantic coast and English Channel. Monitoring revealed that these toxic events have become more frequent since the year 2000, but with varying magnitudes, frequencies and timing depending on the bay. Two bays, located in southern Brittany, exhibited both recurrent contaminations and high P.-nitzschia abundances. The Brest bay and the Seine bay were intermittently affected. The Pertuis Breton exhibited only one major toxic event related to an exceptionally intense bloom of P.-nitzschia in 2010, and the Saint Brieuc bay neither showed significant contamination nor high P.-nitzschia abundance. While high P.-nitzschia abundance appeared to be correlated to scallop toxicity, this study highlights the difficulty in linking P.-nitzschia spp. blooms to king scallop contamination through monitoring. Indeed, P.-nitzschia was determined at the genus level and data regarding species abundances and their toxicity levels are an absolute prerequisite to further assess the environmental control of ASP events. As results describe distinct P.-nitzschia bloom dynamics along the French coast, this may suggest distinct controlling factors. They also revealed that major climatic events, such as the winter storm Xynthia in 2010, can trigger toxicity in P.-nitzschia over a large spatial scale and impact king scallop fisheries all along the coast.

Effects of Organic and Inorganic Nitrogen on the Growth and Production of Domoic Acid by Pseudo-nitzschia multiseries and P. australis (Bacillariophyceae) in Culture

Over the last century, human activities have altered the global nitrogen cycle, and anthropogenic inputs of both inorganic and organic nitrogen species have increased around the world, causing significant changes to the functioning of aquatic ecosystems. The increasing frequency of Pseudo-nitzschia spp. in estuarine and coastal waters reinforces the need to understand better the environmental control of its growth and domoic acid (DA) production. Here, we document Pseudo-nitzschia spp. growth and toxicity on a large set of inorganic and organic nitrogen (nitrate, ammonium, urea, glutamate, glutamine, arginine and taurine). Our study focused on two species isolated from European coastal waters: P. multiseries CCL70 and P. australis PNC1. The nitrogen sources induced broad differences between the two species with respect to growth rate, biomass and cellular DA, but no specific variation could be attributed to any of the inorganic or organic nitrogen substrates. Enrichment with ammonium resulted in an enhanced growth rate and cell yield, whereas glutamate did not support the growth of P. multiseries. Arginine, glutamine and taurine enabled good growth of P. australis, but without toxin production. The highest DA content was produced when P. multiseries grew with urea and P. australis grew with glutamate. For both species, growth rate was not correlated with DA content but more toxin was produced when the nitrogen source could not sustain a high biomass. A significant negative correlation was found between cell biomass and DA content in P. australis. This study shows that Pseudo-nitzschia can readily utilize organic nitrogen in the form of amino acids, and confirms that both inorganic and organic nitrogen affect growth and DA production. Our results contribute to our understanding of the ecophysiology of Pseudo-nitzschia spp. and may help to predict toxic events in the natural environment.

Common European harmful algal blooms affect the viability and innate immune responses of Mytilus edulis larvae

Like marine diseases, harmful algal blooms (HABs) are globally increasing in frequency, severity and geographical scale. As a result, bivalves will have to face the combined threat of toxic algae and marine pathogens more frequently in the (near) future. These stressors combined may further affect the recruitment of ecologically and economically important bivalve species as HABs can affect the growth, viability and development of their larvae. To date, little is known on the specific effects of HABs on the innate immune system of bivalve larvae. This study therefore investigates whether two common harmful algae can influence the larval viability, development and immunological resilience of the blue mussel Mytilus edulis. Embryos of this model organism were exposed (48 h) to five densities of Pseudo-nitzschia multiseries or Prorocentrum lima cells. In addition, the effect of six concentrations of their respective toxins: domoic acid (DA) and okadaic acid (OA) were assessed. OA was found to significantly reduce larval protein phosphatase activity (p < 0.001) and larval viability (p < 0.01) at concentrations as low as 37.8 μg l(-1). P. multiseries (1400 cells ml(-1)), P. lima (150 cells ml(-1)) and DA (dosed five times higher than typical environmental conditions i.e. 623.2 μg l(-1)) increased the phenoloxidase (PO) innate immune activity of the mussel larvae. These results suggest that the innate immune response of even the earliest life stages of bivalves is susceptible to the presence of HABs.

Low-Molecular-Weight Metabolites from Diatoms: Structures, Biological Roles and Biosynthesis

Diatoms are abundant and important biological components of the marine environment that biosynthesize diverse natural products. These microalgae are rich in various lipids, carotenoids, sterols and isoprenoids, some of them containing toxins and other metabolites. Several groups of diatom natural products have attracted great interest due to their potential practical application as energy sources (biofuel), valuable food constituents, and prospective materials for nanotechnology. In addition, hydrocarbons, which are used in climate reconstruction, polyamines which participate in biomineralization, new apoptotic agents against tumor cells, attractants and deterrents that regulate the biochemical communications between marine species in seawaters have also been isolated from diatoms. However, chemical studies on these microalgae are complicated by difficulties, connected with obtaining their biomass, and the influence of nutrients and contaminators in their environment as well as by seasonal and climatic factors on the biosynthesis of the corresponding natural products. Overall, the number of chemically studied diatoms is lower than that of other algae, but further studies, particularly those connected with improvements in the isolation and structure elucidation technique as well as the genomics of diatoms, promise both to increase the number of studied species with isolated biologically active natural products and to provide a clearer perception of their biosynthesis.

Molecular detection of a potentially toxic diatom species

A few diatom species produce toxins that affect human and animal health. Among these, members of the Pseudo-nitzschia genus were the first diatoms unambiguously identified as producer of domoic acid, a neurotoxin affecting molluscan shell-fish, birds, marine mammals, and humans. Evidence exists indicating the involvement of another diatom genus, Amphora, as a potential producer of domoic acid. We present a strategy for the detection of the diatom species Amphora coffeaeformis based on the development of species-specific oligonucleotide probes and their application in microarray hybridization experiments. This approach is based on the use of two marker genes highly conserved in all diatoms, but endowed with sufficient genetic divergence to discriminate diatoms at the species level. A region of approximately 450 bp of these previously unexplored marker genes, coding for elongation factor 1-a (eEF1-a) and silicic acid transporter (SIT), was used to design oligonucleotide probes that were tested for specificity in combination with the corresponding fluorescently labeled DNA targets. The results presented in this work suggest a possible use of this DNA chip technology for the selective detection of A. coffeaeformis in environmental settings where the presence of this potential toxin producer may represent a threat to human and animal health. In addition, the same basic approach can be adapted to a wider range of diatoms for the simultaneous detection of microorganisms used as biomarkers of different water quality levels.

Domoic acid toxicokinetics in Dungeness crabs: new insights into mechanisms that regulate bioaccumulation

Domoic acid (DA) is an excitatory neurotoxic amino acid produced by several marine algal species and is the causative agent of amnesic shellfish poisoning. Profound differences in the toxicokinetics of DA have been identified in a wide variety of shellfish. We characterized the toxicokinetics of DA in Dungeness crabs (Metacarcinus magister) after oral and intravascular dosing (IV) using a variety of doses ranging from 0.1 to 20mg/kg. After a 1mg/kg oral dose, DA disappeared from the foregut within 2h and largely accumulated in the hepatopancreas, with hemolymph and other tissues having 100-1000 times lower concentrations. After IV dosing, hemolymph concentrations of DA were unexpectedly high and toxicokinetic analysis indicated the steady-state volume of distribution (Vss) was 123-197 ml/kg, which is well below the hemolymph volume of 350 ml/kg for crabs. This indicated only limited extravascular distribution of DA was occurring after IV injection, which is surprising considering the capacity of the hepatopancreas to sequester DA after oral dosing. Additional studies measured the partitioning of DA in hepatopancreas cellular and subcellular fractions. The subcellular distribution of DA was primarily associated with the S8 fraction and could be filtered through a 30,000 MW cut-off filter, indicating DA was not appreciably bound to macromolecules. Interestingly, very little (<0.4%) of the total hepatopancreas DA tissue content was associated with the cellular fraction isolated after dissociation and separation from tissue fragments. The in vivo and in vitro results led us to hypothesize that DA uptake and distribution is regulated by crustacean orthologs of ATP-binding cassette (ABC) type transporters. We tested this hypothesis by co-exposing crabs to DA and known inhibitors of ABC transporters (verapamil, cyclosporine A and MK-571) and through in vitro studies using isolated hepatopancreas tissue and mixed cell suspensions prepared from hepatopancreas tissue. The in vivo results were inconclusive in that the toxicokinetics of DA was not consistently altered by co-administration of the inhibitors. Two exceptions were MK-571, which significantly increased the total body clearance of DA and co-administration of verapamil, which significantly increased the hepatopancreas tissue content of DA 24h after IV injection. Isolated pieces of hepatopancreas tissue were able to readily absorb DA from incubation media, but mixed cell suspensions did not. The absorption of DA or lack thereof was largely unaffected by co-incubation with verapamil although cell suspensions appeared to accumulate small quantities of DA in the presence of verapamil. Collectively, the results of this study suggest DA accumulates in the extracellular spaces of the hepatopancreas, such as the tubular lumen. Under natural circumstances, crabs feeding on contaminated shellfish would be expected to readily absorb DA, which is then stored and slowly eliminated in urine. If the DA exposure level exceeds the storage capacity of the tissue (as occurred with the 20mg/kg dose), breakthrough occurs resulting in much higher systemic exposure and potential for DA toxicity.

Management of domoic acid monitoring in shellfish from the Catalan coast

Monitoring of amnesic shellfish poisoning (ASP) toxins in shellfish from the Catalan coast started in 2001. No ASP toxins were detected in any of the analyses performed before 2008. On 22 January 2008, domoic acid (DA) was detected in Donax trunculus (0.5 mg kg(-1)) and confirmed by rapid resolution liquid chromatography-tandem mass spectrometry (0.6 mg kg(-1)). A total of 974 shellfish samples were analyzed from January 2008 to December 2011, covering all the Catalan production areas and the most important marketed species. DA was detected in 23.8 % of the samples and was recorded every month in all areas and all species, except Ostrea edulis, although the percentage of samples with DA and DA content varied widely among samples. DA exceeded the regulatory level of 20 mg kg(-1) twice: in Callista chione sampled on February 2008 and in D. trunculus sampled on April 2010. DA content in Bolinus brandaris appeared constant and close to 4.5 mg kg(-1) for months in 2009. Mytilus galloprovincialis, Crassostrea gigas, and Ruditapes sp. presented very low concentrations of DA in the Ebro Delta bays, despite 113 alert situations according to Pseudo-nitzschia spp. abundances and the high number of shellfish samples analyzed. The origin of DA in Catalan shellfish remains unknown.

Defining and modeling known adverse outcome pathways: Domoic acid and neuronal signaling as a case study

An adverse outcome pathway (AOP) is a sequence of key events from a molecular-level initiating event and an ensuing cascade of steps to an adverse outcome with population-level significance. To implement a predictive strategy for ecotoxicology, the multiscale nature of an AOP requires computational models to link salient processes (e.g., in chemical uptake, toxicokinetics, toxicodynamics, and population dynamics). A case study with domoic acid was used to demonstrate strategies and enable generic recommendations for developing computational models in an effort to move toward a toxicity testing paradigm focused on toxicity pathway perturbations applicable to ecological risk assessment. Domoic acid, an algal toxin with adverse effects on both wildlife and humans, is a potent agonist for kainate receptors (ionotropic glutamate receptors whose activation leads to the influx of Na(+) and Ca²(+)). Increased Ca²(+) concentrations result in neuronal excitotoxicity and cell death, primarily in the hippocampus, which produces seizures, impairs learning and memory, and alters behavior in some species. Altered neuronal Ca²(+) is a key process in domoic acid toxicity, which can be evaluated in vitro. Furthermore, results of these assays would be amenable to mechanistic modeling for identifying domoic acid concentrations and Ca²(+) perturbations that are normal, adaptive, or clearly toxic. In vitro assays with outputs amenable to measurement in exposed populations can link in vitro to in vivo conditions, and toxicokinetic information will aid in linking in vitro results to the individual organism. Development of an AOP required an iterative process with three important outcomes: a critically reviewed, stressor-specific AOP; identification of key processes suitable for evaluation with in vitro assays; and strategies for model development.

Analytical approaches for an important shellfish poisoning agent: domoic Acid

Domoic acid (DA), a neurotoxic amino acid produced by some strains of phytoplankton, is responsible for the human toxic syndrome amnesic shellfish poisoning. This exocitotoxin results in neuronal degeneration and necrosis in specific regions of the hippocampus. Because DA accumulates mostly in shellfish, causing outbreaks in different countries, screening for DA has been carried out with various assays. Although bioassays and immunoassays have been developed, several liquid chromatographic methods for the determination of DA in different matrices such as shellfish, algae, or seawater have been reported. Additionally, other alternative methods such as capillary electrophoresis and capillary electrochromatography have been described. This paper summaries the toxicology, the chemistry, and the developed determination methods of DA.

Domoic acid--a new toxin in the Croatian Adriatic shellfish toxin profile

This is the first study that presents concentrations of domoic acid detected in the whole shellfish tissue from breeding and harvesting areas along the Croatian coast of the Adriatic Sea during the period 2006 to 2008. Shellfish sample analyses after SAX cleaning procedures, using a UV-DAD-HPLC system, showed the presence of domoic acid in four species. The most prevalent of those species were the blue mussel (Mytilus galloprovincialis), followed by European flat oyster (Ostrea edulis), Mediterranean scallop (Pecten jacobaeus) and proteus scallop (Flexopecten proteus). Domoic acid, a potentially lethal phycotoxin that causes amnesic shellfish poisoning (ASP), was detected for the first time in January 2006 with the highest value of 6.5486 μg g⁻¹ in whole shellfish tissue. Pseudo-nitzschia spp. bloom events preceded these high domoic acid concentrations. According to this study, retention of domoic acid in the blue mussel M. galloprovincialis is more than 42 days. This investigation indicates the first presence of domoic acid in Croatian shellfish, but in concentrations under the regulatory limit (20 μg g⁻¹), therefore shellfish consumption was not found to endanger human health.

Shellfish toxicity: human health implications of marine algal toxins

Five major human toxic syndromes caused by the consumption of shellfish contaminated by algal toxins are presented. The increased risks to humans of shellfish toxicity from the prevalence of harmful algal blooms (HABs) may be a consequence of large-scale ecological changes from anthropogenic activities, especially increased eutrophication, marine transport and aquaculture, and global climate change. Improvements in toxin detection methods and increased toxin surveillance programmes are positive developments in limiting human exposure to shellfish toxins.

Use of biosensors as alternatives to current regulatory methods for marine biotoxins

Marine toxins are currently monitored by means of a bioassay that requires the use of many mice, which poses a technical and ethical problem in many countries. With the exception of domoic acid, there is a legal requirement for the presence of other toxins (yessotoxin, saxitoxin and analogs, okadaic acid and analogs, pectenotoxins and azaspiracids) in seafood to be controlled by bioassay, but other toxins, such as palytoxin, cyclic imines, ciguatera and tetrodotoxin are potentially present in European food and there are no legal requirements or technical approaches available to identify their presence. The need for alternative methods to the bioassay is clearly important, and biosensors have become in recent years a feasible alternative to animal sacrifice. This review will discuss the advantages and disadvantages of using biosensors as alternatives to animal assays for marine toxins, with particular focus on surface plasmon resonance (SPR) technology.

The occurrence of domoic acid linked to a toxic diatom bloom in a new potential vector: the tunicate Pyura chilensis (piure)

The tunicate Pyura chilensis (Molina, 1782); Phylum Chordata; Subphylum Urochordata; Class Ascidiacea, common local name "piure" or sea squirt; a filter-feeder (plankton and suspended particles) sessile species; may play an important role in monitoring domoic acid (DA) the principal toxic component of Amnesic Shellfish Poisoning (ASP). Significant DA concentrations have been determined in tunicate samples, collected during a recent ASP outbreak in Bahía Inglesa, an important scallop (Argopecten purpuratus) farming area. Several infaunal species were tested for the presence of DA, in addition to the usual scallop monitoring programme. DA was found at sub-toxic levels in filtering bivalves such as mussels (Mytilus chilensis), large mussels (Aulacomya ater) and clams (Protothaca thaca) (6.4, 5.4 and 4.7 microg DA/g tissue respectively). Of particular interest was the observation of significant accumulations of toxic Pseudo-nitzschia sp. diatoms in the internal siphon and atrium spaces of the tunicate. Toxin distribution within major tunicate organs was heterogeneous with 8.7-15.5 microg DA/g in edible tissues, 14.9-17.9 microg DA/g in the fecal material and 13.6-32.7 microg DA/g in the gut content. DA was determined by HPLC-UV and confirmed by diode-array detection and LC-MS/MS analysis. This is the first report of the presence of DA in a tunicate that is regularly consumed by coastal populations. These results confirm the need to include these organisms in sanitation programs for marine toxins.

Domoic acid induces direct DNA damage and apoptosis in Caco-2 cells: recent advances

Domoic acid (DA) is a neurotoxin produced by sea-water phytoplankton. Shellfish feeding on the phytoplankton can bioconcentrate DA, leading to a potentially serious health hazard for people consuming the contaminated shellfish. DA is the principal toxin responsible for amnesic shellfish poisoning (ASP). The toxic mechanism of DA is believed to be mediated at the level of the mitochondria, where uncoupling of oxidative phosphorylation decreases membrane permeability, causing cell swelling and ultimately lysis. Literature is poor concerning data on the possible genotoxicity and cytotoxicity of DA. In the present study, we have evaluated the cytotoxicity and genotoxicity of DA on a human colorectal adenocarcinoma cell line (Caco-2). Our results clearly demonstrate that DA decreased cell viability (IC(50) about 70 ng/mL), induced direct DNA damage from 15 ng/mL, and apoptosis in Caco-2 cells at 100 ng/mL. This apoptosis is likely bax-dependent and occurred only at high concentrations of DA, while lower concentrations upregulated both bax and bcl-2 at an apparent constant ratio until a sudden decrease of bcl-2 at 100 ng/mL and increase of bax.