The impact of toxic algae on scallop culture and fisheries

Modelling spatiotemporal distributions of Vulcanodinium rugosum and pinnatoxin G in French Mediterranean lagoons: Application to human health risk characterisation

Consumption of seafood contaminated by phycotoxins produced by harmful algae is a major issue in human public health. Harmful algal blooms are driven by a multitude of environmental variables; therefore predicting human dietary exposure to phycotoxins based on these variables is a promising approach in health risk management. In this study, we attempted to predict the human health risks associated with Vulcanodinium rugosum and its neurotoxins, pinnatoxins (PnTXs), which have been regularly found in Mediterranean lagoons since their identification in 2011. Based on environmental variables collected over 1 year in four Mediterranean lagoons, we developed linear mixed models to predict the presence of V. rugosum and PnTX G contamination of mussels. We found that the occurrence of V. rugosum was significantly associated with seawater temperature. PnTX G contamination of mussels was highest in summer but persisted throughout the year. This contamination was significantly associated with seawater temperature and the presence of V. rugosum with a time lag, but not with dissolved PnTX G in seawater. By using the contamination model predictions and their potential variability/uncertainty, we calculated the human acute dietary exposures throughout the year and predicted that 25% of people who consume mussels could exceed the provisional acute benchmark value during the warmest periods. We suggest specific recommendations to monitor V. rugosum and PnTX G.

Marine Biotoxins in Whole and Processed Scallops from the Argentine Sea

Harmful algal blooms are an increasing worldwide threat to the seafood industry and human health as a consequence of the natural production of biotoxins that can accumulate in shellfish. In the Argentine Sea, this has been identified as an issue for the offshore fisheries of Patagonian scallops (Zygochlamys patagonica), leading to potentially harmful effects on consumers. Here we assess spatial and temporal patterns in marine biotoxin concentrations in Patagonian scallops harvested in Argentinian waters between 2012-2017, based on analyses for paralytic shellfish toxins, lipophilic toxins, and amnesic shellfish toxins. There was no evidence for concentrations of lipophilic or amnesic toxins above regulatory acceptance thresholds, with trace concentrations of pectenotoxin 2, azaspiracid 2 and okadaic acid group toxins confirmed. Conversely, paralytic shellfish toxins were quantified in some scallops. Gonyautoxins 1 and 2 dominated the unusual toxin profiles (91%) in terms of saxitoxin equivalents with maximum concentrations reaching 3985 µg STX eq/kg and with changes in profiles linked in part to seasonal changes. Total toxin concentrations were compared between samples of the adductor muscle and whole tissue, with results showing the absence of toxins in the adductor muscle confirming toxin accumulation in the digestive tracts of the scallops and the absence of a human health threat following the processing of scallop adductor meat. These findings highlight that paralytic shellfish toxins with an unusual toxin profile can occur in relatively high concentrations in whole Patagonian scallops in specific regions and during particular time periods, also showing that the processing of scallops on board factory ships to obtain frozen adductor muscle is an effective management process that minimizes the risk of poisonings from final products destined for human consumption.

Shellfish Toxin Uptake and Depuration in Multiple Atlantic Canadian Molluscan Species: Application to Selection of Sentinel Species in Monitoring Programs

Shellfish toxin monitoring programs often use mussels as the sentinel species to represent risk in other bivalve shellfish species. Studies have examined accumulation and depuration rates in various species, but little information is available to compare multiple species from the same harvest area. A 2-year research project was performed to validate the use of mussels as the sentinel species to represent other relevant eastern Canadian shellfish species (clams, scallops, and oysters). Samples were collected simultaneously from Deadmans Harbour, NB, and were tested for paralytic shellfish toxins (PSTs) and amnesic shellfish toxin (AST). Phytoplankton was also monitored at this site. Scallops accumulated PSTs and AST sooner, at higher concentrations, and retained toxins longer than mussels. Data from monitoring program samples in Mahone Bay, NS, are presented as a real-world validation of findings. Simultaneous sampling of mussels and scallops showed significant differences between shellfish toxin results in these species. These data suggest more consideration should be given to situations where multiple species are present, especially scallops.

Rapid Domoic Acid Depuration in the Scallop Argopecten purpuratus and Its Transfer from the Digestive Gland to Other Organs

Domoic acid (DA), the main toxin responsible for Amnesic Shellfish Poisoning, frequently affects the marine resources of Chile and other countries across the South Pacific, thus becoming a risk for human health. One of the affected resources is the scallop Argopecten purpuratus. Even though this species has a high commercial importance in Northern Chile and Peru, the characteristics of its DA depuration are not known. In this work, the DA depuration was studied by means of two experiments: one in controlled (laboratory) and another in natural conditions. All organs of A. purpuratus depurated the toxin very quickly in both experiments. In some organs, an increase or a very small decrease of toxin was detected in the early depuration steps. Several models were used to describe this kinetics. The one that included toxin transfer between organs and independent depuration from each organ was the model that best fit the data. It seems, therefore, that the DA in this species is quickly transferred from the digestive gland to all other organs, which release it into the environment. Physiological differences in the two experiments have been shown to have some effect on the depuration from each organ but the actual reasons are still unknown.

The gene-rich genome of the scallop Pecten maximus

BACKGROUND

The king scallop, Pecten maximus, is distributed in shallow waters along the Atlantic coast of Europe. It forms the basis of a valuable commercial fishery and plays a key role in coastal ecosystems and food webs. Like other filter feeding bivalves it can accumulate potent phytotoxins, to which it has evolved some immunity. The molecular origins of this immunity are of interest to evolutionary biologists, pharmaceutical companies, and fisheries management.

FINDINGS

Here we report the genome assembly of this species, conducted as part of the Wellcome Sanger 25 Genomes Project. This genome was assembled from PacBio reads and scaffolded with 10X Chromium and Hi-C data. Its 3,983 scaffolds have an N50 of 44.8 Mb (longest scaffold 60.1 Mb), with 92% of the assembly sequence contained in 19 scaffolds, corresponding to the 19 chromosomes found in this species. The total assembly spans 918.3 Mb and is the best-scaffolded marine bivalve genome published to date, exhibiting 95.5% recovery of the metazoan BUSCO set. Gene annotation resulted in 67,741 gene models. Analysis of gene content revealed large numbers of gene duplicates, as previously seen in bivalves, with little gene loss, in comparison with the sequenced genomes of other marine bivalve species.

CONCLUSIONS

The genome assembly of P. maximus and its annotated gene set provide a high-quality platform for studies on such disparate topics as shell biomineralization, pigmentation, vision, and resistance to algal toxins. As a result of our findings we highlight the sodium channel gene Nav1, known to confer resistance to saxitoxin and tetrodotoxin, as a candidate for further studies investigating immunity to domoic acid.

Detección de biotoxinas en moluscos de venta al consumidor en la Comunidad de Madrid

La presencia de biotoxinas en los moluscos es largamente conocida y ampliamente vigilada. En España, las dos que más se han detectado en los últimos años han sido las saxitoxinas y el ácido okadaico (toxinas PSP y DSP, respectivamente). A efecto de evitar intoxicaciones agudas en la población, existen unos límites máximos de toxinas que pueden estar presentes en el alimento de venta al consumidor. Sin embargo, la presencia de toxina a concentraciones inferiores a la legalmente establecida puede producir intoxicaciones crónicas o efectos a largo plazo. El objetivo del estudio es detectar la presencia de toxinas que están llegando a consumo humano, estén o no dentro del límite de concentración permitido. Se realizó un muestreo en diferentes pescaderías de la Comunidad de Madrid, sin incluir la propia ciudad de Madrid, y se analizó la concentración de toxinas PSP y DSP presentes en 50 muestras de mejillones, almejas, berberechos, vieiras y zamburiñas. Los resultados indican que un 4% de las muestras de los moluscos adquiridos contenían saxitoxinas y en un 6% se detectó ácido okadaico, ya sea en forma de trazas o con una positividad confirmada en base al método analítico, si bien los datos obtenidos cumplen los límites máximos establecidos a nivel comunitario.

Distribution of Tetrodotoxin in the New Zealand Clam, Paphies australis, Established Using Immunohistochemistry and Liquid Chromatography-Tandem Quadrupole Mass Spectrometry

Tetrodotoxin (TTX) is one of the most potent neurotoxins known. It was originally thought to only occur in puffer fish but has now been identified in twelve different classes of freshwater and marine organisms, including bivalves. Despite being one of the world’s most studied biotoxins, its origin remains uncertain. There is contradictory evidence regarding the source of TTX and its pathway through food webs. To date, the distribution of TTX has not been examined in bivalves. In the present study, 48 Paphies australis, a TTX-containing clam species endemic to New Zealand, were collected. Thirty clams were dissected, and organs and tissues pooled into five categories (siphons, digestive gland, adductor muscles, and the ‘rest’) and analyzed for TTX using liquid chromatography-mass spectrometry (LC-MS). The micro-distribution of TTX was visualized in the remaining 18 individuals using an immunohistological technique incorporating a TTX-specific monoclonal antibody. The LC-MS analysis revealed that siphons contained the highest concentrations of TTX (mean 403.8 µg/kg). Immunohistochemistry analysis showed TTX in the outer cells of the siphons, but also in the digestive system, foot, and gill tissue. Observing TTX in organs involved in feeding provides initial evidence to support the hypothesis of an exogenous source in P. australis.

Hsp70 gene expansions in the scallop Patinopecten yessoensis and their expression regulation after exposure to the toxic dinoflagellate Alexandrium catenella

Heat shock protein 70 (Hsp70s) family members are present in virtually all living organisms and perform a fundamental role against different types of environmental stressors and pathogenic organisms. Marine bivalves live in highly dynamic environments and may accumulate paralytic shellfish toxins (PSTs), a class of well-known neurotoxins closely associated with harmful algal blooms (HABs). Here, we provide a systematic analysis of Hsp70 genes (PyHsp70s) in the genome of Yesso scallop (Patinopecten yessoensis), an important aquaculture species in China, through in silico analysis using transcriptome and genome databases. Phylogenetic analyses indicated extensive expansion of Hsp70 genes from the Hspa12 sub-family in the Yesso scallop and also the bivalve lineages, with gene duplication events before or after the split between the Yesso scallop and the Pacific oyster. In addition, we determined the expression patterns of PyHsp70s after exposure to Alexandrium catenella, the dinoflagellate producing PSTs. Our results confirmed the inducible expression patterns of PyHsp70s under PSTs stress, and the responses to the toxic stress may have arisen through the adaptive recruitment of tandem duplication of Hsp70 genes. These findings provide a thorough overview of the evolution and modification of the Hsp70 family, which will gain insights into the functional characteristics of scallop Hsp70 genes in response to different stresses.

Accumulation, transformation and breakdown of DSP toxins from the toxic dinoflagellate Dinophysis acuta in blue mussels, Mytilus edulis

Okadaic acid (OA), dinophysistoxins (DTX) and pectenotoxins (PTX) produced by the dinoflagellates Dinophysis spp. can accumulate in shellfish and cause diarrhetic shellfish poisoning upon human consumption. Shellfish toxicity is a result of algal abundance and toxicity as well as accumulation and depuration kinetics in mussels. We mass-cultured Dinophysis acuta containing OA, DTX-1b and PTX-2 and fed it to the blue mussel, Mytilus edulis under controlled laboratory conditions for a week to study toxin accumulation and transformation. Contents of OA and DTX-1b in mussels increased linearly with incubation time, and the net toxin accumulation was 66% and 71% for OA and DTX-1b, respectively. Large proportions (≈50%) of both these toxins were transformed to fatty acid esters. Most PTX-2 was transformed to PTX-2 seco-acid and net accumulation was initially high, but decreased progressively throughout the experiment, likely due to esterification and loss of detectability. We also quantified depuration during the subsequent four days and found half-life times of 5-6 days for OA and DTX-1b. Measurements of dissolved toxins revealed that depuration was achieved through excreting rather than metabolizing toxins. This is the first study to construct a full mass balance of DSP toxins during both accumulation and depuration, and we demonstrate rapid toxin accumulation in mussels at realistic in situ levels of Dinophysis. Applying the observed accumulation and depuration kinetics, we model mussel toxicity, and demonstrate that a concentration of only 75 Dinophysis cells l(-1) is enough to make 60 mm long mussels exceed the regulatory threshold for OA equivalents.

Depuration and anatomical distribution of domoic acid in the surf clam Mesodesma donacium

In northern Chile, domoic acid (DA) has been detected in several bivalve species. In Mesodesma donacium, one of the most important commercial species for local fishermen, no information is available on depuration, or on the anatomical distribution of this toxin and its potential use as a palliative measure to minimize the consequences of ASP outbreaks. Deputation of DA is very fast in M. donacium, and can be adequately described by means of a two-compartment model. The estimated rates for the first and second compartments were 1.27 d(-1) and 0.24 d(-1), respectively, with a transfer rate between compartments of 0.75. Having high depuration rates protects this species from being affected by Pseudo-nitzschia blooms for an extended period of time. Taking this into account, the time in which the bivalves are unsafe for consumers is very short, and therefore the economic losses that could result by the DA outbreaks in local fisheries should be moderate. In relation to anatomical distribution, at least during the uptake phase, the toxin was evenly distributed within the soft tissues, with a total toxin burden corresponding to 27%, 32% and 41% for Digestive Gland (DG), Foot (FT) and Other Body Fractions (OBF), respectively. Since the contribution of each organ to the toxin concentration is a function of both weight contribution and toxin burden, the pattern of toxin distribution showed the following trend: "all other body fractions" (OBF) > Foot (FT) > Digestive Gland (DG). Thus, the highest concentration of DA, with a contribution close to 72%, corresponds to the edible tissues (OBF + FT), while the DG (non-edible tissue) only contributes the remaining 28%. Consequently, in view of the anatomical distribution of domoic acid in M. donacium, the elimination of the digestive gland does not substantially reduce the toxicity of the final product and therefore selective evisceration would not improve their quality for human consumption.

Evaluation of the production of paralytic shellfish poisoning toxins by extracellular bacteria isolated from the toxic dinoflagellate Alexandrium minutum

The purpose of the study was to determine if paralytic shellfish poisoning (PSP) toxins are present in extracellular bacteria isolated from a toxic strain of the dinoflagellate Alexandrium minutum. A quantitative analysis was carried out of viable culturable bacteria attached to the surface of dinoflagellates and of bacteria present in dinoflagellate culture medium. A numerical taxonomy study was undertaken for presumptive identification of bacteria attached to the surface of dinoflagellates. Members of the following genera were detected on the cell surface of A. minutum: Cellulophaga, Marinomonas, Pseudoalteromonas, and Vibrio. The presence of intracellular PSP toxins in bacteria isolated from the cell surface of dinoflagellates was analysed by high-performance liquid chromatography with fluorescence detection (HPLC-FLD). Compounds that eluted at the same time as the standards of the PSP toxins GTX-2, GTX-3, GTX-4, dcGTX-2, and dcGTX-3 were present in some of the bacterial cell extracts. Natural fluorescent bacterial compounds, coeluting with some PSP toxins, were also detected. The results obtained showed that the fluorescent compounds, identified as putative PSP toxins by HPLC-FLD, did not correspond to any PSP analogue. This allowed us to reject the hypothesis that extracellular bacteria attached to the surface of dinoflagellates produce PSP toxins.

Accumulation of paralytic shellfish toxins by surfclams, Spisula solidissima (Dillwyn, 1897) in the Gulf of Maine: seasonal changes, distribution between tissues, and notes on feeding habits

Accumulation of paralytic shellfish poisoning (PSP) toxins by surfclams, Spisula solidissima, was studied over a period of two years at two inshore locations in southern Maine and at six stations on Georges Bank in the Gulf of Maine. Whole animals as well as individual tissues (siphon, mantle, digestive gland, foot, adductor muscle, gill) were analyzed for PSP-toxicity levels using the standard AOAC mouse bioassay. Analyses of gut contents were carried out on surfclams from both inshore and offshore locations to identify the type of particles ingested. Surfclams feed primarily on phytoplankton and detrital material characteristic of the overlying seawater and surface sediment. No evidence was found for any selection based on particle size or type. Elevated levels of PSP toxins were noted in surfclams from Georges Bank more than two years after initial toxification. Toxins were not evenly distributed among the various tissues of surfclams. Initially, maximum toxicity among surfclam tissues was found in digestive glands; however, subsequent analyses of samples collected later in the year indicated that toxicity in gill and mantle tissues had increased relative to initial values. No toxicity was detected in adductor muscles. Surfclams are characterized by a high variation in total toxin load among individual animals, with a tendency for decreasing variation as toxin levels increase. Archived data from the Main Department of Marine Resources revealed annual and seasonal patterns of toxin accumulation by surfclams, i.e., toxin accumulation is an annual event, with initial increases in toxicity usually occurring in early spring.