Effects of the toxic dinoflagellate Protoceratium reticulatum and its yessotoxins on the survival and feed ingestion of Argopecten purpuratus veliger larvae.

The effects of yessotoxins (YTXs) produced by the dinoflagellate Protoceratium reticulatum in the early stages of bivalves have not been studied in detail. The present study evaluates the effects of P. reticulatum and YTXs on the survival and feed ingestion of veliger larvae of Argopecten purpuratus. Larvae were 96 h-exposed to 500, 1000 and 2000 P. reticulatum cells mL-1, and their equivalent YTX extract was prepared in methanol. Results show a survival mean of 82 % at the highest density of dinoflagellate, and 38 % for larvae with the highest amount of YTX extract. Feed ingestion is reduced in the dinoflagellate exposure treatments as a function of cell density. Therefore, the effect of YTXs on A. purpuratus represents a new and important area of study for investigations into the deleterious effects of these toxins in the early stages of the life cycle of this and, potentially, other bivalves.

Biochemical response and tissue-specific accumulation of scallop Aequipecten tehuelchus from Patagonia, Argentina after exposure to inorganic arsenic.

This study investigates the effects of different inorganic arsenic (As III) concentrations (0, 125, 500 and 1000 µg As/L) following two exposure times (7 and 14 days) on gills, digestive gland and muscle of scallop Aequipecten tehuelchus from Patagonia, Argentina. A biochemical approach was used to investigate oxidative stress-related parameters after different As concentrations and exposure times. Although the accumulation of As was of the same order of magnitude in all tissues, the results showed distinct tissue-specific oxidative responses to this metalloid. Furthermore, the variation in exposure time had no significant effect on As accumulation in any of the three tissues. In gills, despite no reactive oxygen and nitrogen species (RONS) were detected, there was an increase in catalase (CAT) activity and metallothionein (MT) levels. Conversely, digestive gland showed RONS production without a rise in CAT and glutathione S-transferases (GST) activities, but with an increase in MT levels. In muscle, RONS production and CAT activity kept constant or decreased, while MT levels remained unchanged. In addition, exposure time demonstrated its critical role in gills by influencing the response of CAT, GST and MT, particularly at high As concentrations, while exposure time did not affect the biochemical stress parameters in the digestive gland and muscle. Interestingly, neither concentration of As produced lipid damage, showing the effectiveness of the antioxidant mechanisms to avoid it. These results emphasize that A. tehuelchus exhibited no time-dependent effects in response to As exposure, while showing tissue-specific responses characterized by significant concentration-dependent effects of As. This study provides a comprehensive insight by considering the combined effects of time and concentration of a contaminant and distinguishing its effects on specific tissues, a dimension often overlooked in the existing literature. Subsequent studies should prioritize the analysis of additional contaminants in species with increased sensitivity.

The toxic dinoflagellate Alexandrium catenella adversely affects early life stages of tehuelche scallop.

The effects of the toxic dinoflagellate Alexandrium catenella were investigated on growth, survival, and histopathology in larvae and spat of the Tehuelche scallop Aequipecten tehuelchus from Patagonia, Argentina. The study consisted of laboratory incubations of scallop larvae/spat with A. catenella, using environmentally realistic abundances of the dinoflagellate. Survival, growth, and histopathological effects were documented for scallop larvae/spat before, during, and after 7-day-long exposure to A. catenella. The scallops were grouped in flasks containing 0 (control), 20, 200, and 2000 cells mL-1 of A. catenella. The presence of A. catenella induced reduced larvae survival after 24 h, whereas a clear effect was observed after 3 days (survival of control larvae 95%, 72, and 79% for 20 and 200 cells mL-1, respectively, and 43% for 2000 cells mL-1). The growth rates of the control larvae and those exposed to 20 mL-1 cells were significantly different from zero. Histopathological effects (melanization, loss of connective tissue, necrosis, and inflammatory responses) were observed in spat exposed to A. catenella. These effects were more pronounced at the highest dinoflagellate concentration. Blooms of A. catenella frequently coincide with the reproductive season of A. tehuelchus, thus there is a need to further study the relationship between harmful algal blooms and the effect on scallops' natural populations in the region.

Collapse of scallop Nodipecten nodosus production in the tropical Southeast Brazil as a possible consequence of global warming and water pollution.

Mollusc rearing is a relevant global socioeconomic activity. However, this activity has faced severe problems in the last years in southeast Brazil. The mariculture scallop production dropped from 51,2 tons in 2016 to 10,2 tons in 2022 in the Baia da Ilha Grande (BIG; Rio de Janeiro). However, the possible causes of this collapse are unknown. This study aimed to analyze decadal trends of water quality in Nodipecten nodosus spat and adult production in BIG. We also performed physical-chemical and biological water quality analyses of three scallop farms and two nearby locations at BIG in 2022 to evaluate possible environmental stressors and risks. Scallop spat production dropped drastically in the last five years (2018-2022: mean ± stdev: 0.47 ± 0.45 million). Spat production was higher in colder waters and during peaks of Chlorophyll a in the last 13 years. Reduction of Chlorophyll a coincided with decreasing spat production in the last five years. Warmer periods (>27 °C) of the year may hamper scallop development. Counts of potentially pathogenic bacteria (Vibrios) and Escherichia coli were significantly higher in warmer periods which may further reduce scallop productivity. Shotgun metagenomics of seawater samples from the five studied corroborated these culture-based counts. Vibrios and fecal indicator bacteria metagenomic sequences were abundant across the entire study area throughout 2022. The results of this study suggest the collapse of scallop mariculture is the result of a synergistic negative effect of global warming and poor seawater quality.

Resistance of Argopecten purpuratus scallop larvae to vibriosis is associated with the front-loading of immune genes and enhanced antimicrobial response.

Mass mortality events caused by vibriosis have emerged in hatchery-reared scallop larvae from Chile, threatening scallop aquaculture. In an attempt to mitigate this emerging infectious disease and provide candidates for marker-assisted selective breeding, we tested here the existence of a genetic component of Argopecten purpuratus scallop resistance to the pathogen Vibrio bivalvicida. Through a dual RNA-seq approach we analyzed the basal transcriptome and the transcriptional response to infection in two resistant and two susceptible families as well as the pathogen transcriptomic response to host colonization. The results highlighted a genetic basis in the resistance of scallop larvae to the pathogen. The Vibrio response was characterized by a general metabolic adaptation to the host environment, along with several predicted virulence factors overexpressed in infected scallop larvae with no difference between resistant and susceptible host phenotypes. On the host side, several biological processes were enriched in uninfected resistant larvae. Within these enriched categories, immune-related processes were overexpressed, while morphogenesis, biomineral tissue development, and angiogenesis were under expressed. Particularly, genes involved in immune recognition and antimicrobial response, such as lipopolysaccharide-binding proteins (LBPs), lysozyme, and bactericidal permeability-increasing protein (BPI) were overexpressed in uninfected resistant larvae. As expected, immune-related biological processes were enriched in Vibrio-infected larvae, but they were more numerous in resistant larvae. Overexpressed immune genes in response to infection included several Toll-like receptors, TNF and NF-κB immune signaling genes, and the antimicrobial peptide Big defensin ApBD1. Results strongly suggest that both a front-loading of immune genes and an enhanced antimicrobial response to infection contribute to the resistance, while pathogen infective strategy does not discriminate between host phenotypes. Overall, early expression of host immune genes appears as a strong determinant of the disease outcome that could be used in marker-assisted selective breeding.

Differential gene expression analysis in the scallop Argopecten purpuratus exposed to altered pH and temperature conditions in an upwelling-influenced farming area.

Increased carbon dioxide in the atmosphere and its absorption across the ocean surface will alter natural variations in pH and temperature levels, occurring in coastal upwelling ecosystems. The scallop Argopecten purpuratus, one of the most economically important species farmed in northern Chile, has been shown to be vulnerable to these environmental drivers. However, the regulatory responses at the gene-level of scallops to these climate stressors remain almost unknown. Consequently, we used an orthogonal experimental design and RNAseq approach to analyze the acute effects of variability in pH and temperature on gene expression in the muscle tissue of A. purpuratus. In respect to control conditions (pH ~ 8.0/ 14 °C), the influence of low pH (~ 7.7) and temperature (14 °C) induced the activation of several genes associated with apoptotic signaling pathways and protein localization to plasma membrane. Elevated temperature (18 °C) and pH (~8.0) conditions increased the expression of transcripts associated with the activation of muscle contraction, regulation, and sarcomere organization effects on muscle tissue. In scallops exposed to low pH and elevated temperature, the genes expressed were differentially associated with the oxidation-reduction process, signal translation, and positive regulation of GTPase activity. These results indicated that the differentially expressed genes under the experimental conditions tested are mainly related to the mitigation of cellular damage and homeostasis control. Our results add knowledge about the function of the adductor muscle in response to stressors in scallops. Furthermore, these results could help in the identification of molecular biomarkers of stress necessary to be integrated into the aquaculture programs for the mitigation of climate change.

Description of the early shell morphology of three species of Pectinidae (Mollusca: Bivalvia) from Argentina.

We describe the shell morphology of the prodissoconch and early postlarval shell of Aequipecten tehuelchus (dOrbigny), Flexopecten felipponei (Dall), and Zygochlamys patagonica (King) from the southern coast of Argentina. Aequipecten tehuelchus has a nepioconch microsculpture with fine, dense, and regularly distributed pits. The byssal notch is initially deep and narrow but becomes sinuous at the beginning of the post-nepioconch. The nepioconch of Zygochlamys patagonica has antimarginal riblets; the byssal notch is wider than in A. tehuelchus and does not present the sinuosity observed in the other species. The microsculpture of the nepioconchs of F. felipponei and A. tehuelchus is indistinguishable. The earliest differentiation between the two species appears with the post-nepionic left valve, in which A. tehuelchus exhibits between 15 and 20 primary ribs while F. felipponei displays 28 to 34 faint folds. Zygochlamys patagonica shows 21 to 31 primary and secondary ribs. The taxonomic status of the three species is discussed in light of these findings and with respect to current adult-shell taxonomy and genetic analyses.

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.

Effect of low pH on growth and shell mechanical properties of the Peruvian scallop Argopecten purpuratus (Lamarck, 1819).

Dissolution of anthropogenic CO2 modifies seawater pH, leading to ocean acidification, which might affect calcifying organisms such as bivalve mollusks. Along the Peruvian coast, however, natural conditions of low pH (7.6-8.0) are encountered in the habitat of the Peruvian scallop (Argopecten purpuratus), as a consequence of the nearby coastal upwelling influence. To understand the effects of low pH in a species adapted to these environmental conditions, an experiment was performed to test its consequences on growth, calcification, dissolution, and shell mechanical properties in juvenile Peruvian scallops. During 28 days, scallops (initial mean height = 14 mm) were exposed to two contrasted pH conditions: a control with unmanipulated seawater presenting pH conditions similar to those found in situ (pHT = 7.8) and a treatment, in which CO2 was injected to reduce pH to 7.4. At the end of the experiment, shell height and weight, and growth and calcification rates were reduced about 6%, 20%, 9%, and 10% respectively in the low pH treatment. Mechanical properties, such as microhardness were positively affected in the low pH condition and crushing force did not show differences between pH treatments. Final soft tissue weights were not significantly affected by low pH. This study provides evidence of low pH change shell properties increasing the shell microhardness in Peruvian scallops, which implies protective functions. However, the mechanisms behind this response need to be studied in a global change context.

Beach strandings of Tehuelche scallop, Aequipecten tehuelchus, in Patagonia: Multi-scale processes and management implications.

The magnitude and causal mechanisms of a massive beach stranding of Tehuelche scallops that occurred in November 2017 in San José Gulf, Argentina, were investigated with the long-term goal of improving the assessment and management of the scallop fishery. The biomass of scallops washed ashore and deposited over a 10-km stretch of coast was estimated by quadrat sampling and compared with the results of a scallop stock assessment survey conducted three months prior to the stranding event. The resulting estimate of total biomass loss was in the order of 200 t, representing 10% of the estimated total scallop biomass in the San José gulf. The stranding coincided with persistent strong southerly winds (13 m/s) blowing for 24 h in San José Gulf, and large-scale windstorms that affected the southern tip of South America. Surface waves predicted under such windstorm conditions could generate strong bottom orbital velocities at shallow waters (<10 m depth), sufficient to drag and transport ashore scallops by Stokes drift (600-2000 m in 24 h). Analysis of local wind data recorded over a 6.8-year period indicated that such windstorm conditions occurred with an average frequency of 7.7 times per year, implying that beach strandings could have a significant impact on the scallop resource and its fishery. The actual impact of windstorms would depend on the location, depth and size composition of scallop beds, shallow beds (<10 m depth) being more susceptible to stranding risks. The use of spatial harvest control rules, instead of the global total allowable catch used at present, could reduce the risks of yield loss by directing the harvest to the more vulnerable scallop beds.

Analysis and gonadal localization of Speedy A mRNA transcript, a novel gene associated with early germline cells in the scallop, Argopecten purpuratus.

The Speedy A (spdya) gene is a member of the Speedy/RINGO family, encoding a spdya protein associated with cellular cycle and meiosis in vertebrates. Results from genetic analyses indicated spdya conditional knockout mice are sterile, suggesting that this protein has essential functions in mammalian reproduction. There, however, are no published reports on the localization of spdya mRNA in the germline or in somatic cell lineages within the gonads from mollusks or other invertebrate species. Using a previously obtained transcriptome assembly from the scallop Argopecten purpuratus, an economically important hermaphroditic scallop species from Chile and Peru, there was identification of a complete coding sequence of the spdya mRNA. Phylogenetically spdya protein has sequence conservation homology with other scallops and mollusks. The relative mRNA transcript abundances at different gametogenic stages was assessed using quantitative PCR procedures. Results indicated there was an increase of spdya mRNA transcript abundance in testicular region samples at the late active stage, followed by a decrease in testis of reproductively mature individuals. To gain insight into the cellular localization of ap-spdya transcript within the gonads, specific RNA probes were synthesized for in situ hybridization analyses of gonad histological sections. Results indicated spdya mRNA is located exclusively in early germline (previtellogenic oocytes and spermatogonia) and somatic proliferative tissues of A. purpuratus ovarian and testicular regions. Overall, these results indicate there are putative functions of spdya in the early oogenesis and spermatogenesis of A. purpuratus and will contribute to furthering the understanding of gametogenesis in this species.

Big defensin from the scallop Argopecten purpuratus ApBD1 is an antimicrobial peptide which entraps bacteria through nanonets formation.

Big defensins is a large family of antimicrobial peptides found in restricted groups of invertebrates, in particular mollusks where they have highly diversified. Big defensins are composed of a highly hydrophobic N-terminal region and a C-terminal region containing six cysteine residues whose arrangement is identical to that of vertebrate ß-defensins. They have been shown to be active against both Gram-positive and Gram-negative bacteria and fungi. Antimicrobial aggregates called nanonets entrapping and killing bacteria have been recently described for the hydrophobic N-terminal region of the Cg-BigDef1 from the oyster Crassostrea gigas. To determine whether nanonets formation is a conserved trait of mollusk big defensins, we assessed the potential entrapping of bacteria through nanonets of the big defensin from the scallop Argopecten purpuratus, ApBD1. Recombinant ApBD1 was produced with a thrombin-cleavable N-terminal His6 tag, followed by the mature peptide carrying a mutation of the last cysteine residue of the C-terminal region by and arginine, named rApBD1(C87R). This mutation did not apparently affect the three-dimensional structure and the biological properties of rApBD1(C87R), as evidenced by in silico modeling and in vitro antimicrobial assays. Strong immune staining of rApBD1(C87R) in numerous areas surrounding bacteria was observed by confocal microscopy, suggesting that rApBD1(C87R) entraps bacteria in peptide aggregates similar to those reported to the oyster big defensin. This study suggests the conservation of bactericidal activity and nanonet formation across big defensins from bivalve mollusks.

Paralytic shellfish toxins in Peruvian scallops associated with blooms of Alexandrium ostenfeldii (Paulsen) Balech & Tangen in Paracas Bay, Peru.

In recent years, dense Alexandrium ostenfeldii blooms have been reported in different coastal areas. In this study, we report for the first time the occurrence of A. ostenfeldii blooms associated with the detection of paralytic shellfish toxins (PSTs) in the Peruvian scallop (Argopecten purpuratus) from Paracas Bay. Alexandrium ostenfeldii blooms occurred at the end of summer and early fall, after the increase of riverine input and under stratified conditions following a decrease in wind velocity. The highest abundances occurred during warm sea surface temperatures (18-27 °C). High PST concentrations that exceed the maximum permissible level (800 µg STX eq. kg-1) occurred even under low A. ostenfeldii abundances (20 × 103 cells l-1). Our results contribute to a better understanding of the dynamics of A. ostenfeldii in coastal systems influenced by riverine inputs and upwelling and can be used to improve monitoring programs and allow the implementation of mitigation measures along the Peruvian coast.

A switch in species dominance of a recovering pelagic ecosystem.

Although many marine ecosystems have been adversely impacted by human activities,1 some are now recovering due to reductions in fishing pressure.2-4 Here, we document the recovery of an ecosystem subjected to intense anthropogenic activity for over 200 years, the Clyde Sea.5 This region once had productive fisheries for herring (Clupea harengus) and other fish, but these disappeared at the turn of the century.6,7 Using acoustic surveys of the pelagic ecosystem, we found that the Clyde Sea supports 100 times as many forage fish as in the late 1980s. However, herring has now been replaced by sprat (Sprattus sprattus), despite virtually no fishing on herring for 20 years. A combination of a warming sea,6 bycatch of herring in the prawn (Nephrops norvegicus) fishery,8,9 and susceptibility of herring to poor recruitment may have contributed to this unexpected recovery. We compare this to similar unexpected "recoveries" involving unforeseen ecosystem effects, such as the return of hake (Merluccius merluccius) to the North Sea;10,11 the recent expansion of the pelagic squat lobster, "munida," (Pleuroncodes monodon) off Peru;12 and the increase in scallop (Placopecten magellanicus) numbers on Georges Bank.13 The lack of a current sprat fishery in the Clyde presents a unique opportunity to develop an alternative industry for its seafaring community: ecotourism. Charismatic megafauna (whales, dolphins, and seabirds) that people will pay to see14 will, in time-if not already15,16-be drawn in by the abundance of forage fish now present, further restoring the biodiversity of the region after centuries of overexploitation.

Unveiling the unknown phylogenetic position of the scallop Austrochlamys natans and its implications for marine stewardship in the Magallanes Province.

Two species of scallop, Austrochlamys natans ("Ostión del Sur") and Zygochlamys patagonica ("Ostión patagonico") are presently exploited in the southern part of the Magallanes Province (MP). The lack of clarity in taxonomic identification and ecological aspects is generating both erroneous extraction statistics and an unperceived harvesting pressure on A. natans and Z. patagonica. We aim to discriminate these Magallanes scallops accurately, improve our understanding of their complex natural history and discuss possible implications for their management and conservation status, given the current fisheries statistics. To achieve these goals, we present a complete review of the historical identification of the Magallanes scallop and a multi-locus molecular phylogeny which allowed us to recover the phylogenetic position of A. natans. We sampled 54 individuals from five localities across the southern Pacific coast of the MP. We calculated the depth of the byssal notch (BND) and shell height (VH) ratio from morphological characters and conducted phylogenetic reconstructions with mitochondrial (12S and 16S) and nuclear markers (28S) using Bayesian and maximum likelihood analyses. Both morphology and molecular phylogeny identified two distinct entities, Z. patagonica and a distinct, highly divergent lineage that corresponds to A. natans. Our study provides integrative evidence to alert the current fishery management and the need for further conservation studies.

First description outside Europe of the emergent pathogen Vibrio europaeus in shellfish aquaculture.

Vibrio europaeus is an emergent pathogen affecting the most important bivalve species reared in Spanish and French hatcheries. Using a genomic approach, we identified V. europaeus outside Europe for the first time from massive larval mortalities of scallop (Argopecten purpuratus) in Chile and from seawater near a shellfish hatchery in the US West Coast. Results show the worldwide spreading and potential impact of V. europaeus for aquaculture; these four countries are among the 10 major producers of mollusks. Pathogenicity of V. europaeus was demonstrated for the first time towards scallop, the second most important species for Chilean mariculture.

Assessment of the Presence of Lipophilic Phycotoxins in Scallops (Argopecten purpuratus) Farmed along Peruvian Coastal Waters.

ABSTRACT: Some harmful algal blooms produce lipophilic marine biotoxins (LMTs) such as okadaic acid (OA; and its analogs dinophysistoxins [DTXs]), yessotoxins (YTXs), pectenotoxins (PTXs), and azaspiracids (AZAs), all of which may accumulate in filter-feeding bivalve mollusks. European health regulations stipulate a limit of 160 µg/kg for OA or DTXs, PTXs, and AZAs and 3.75 mg/kg for YTXs. Argopecten purpuratus is a valuable commercial marine bivalve exploited in Peru. Despite its importance and the periodic reports of the presence of harmful algal blooms in Peruvian coastal waters, information regarding potential contamination of these scallops by LMTs is lacking. We evaluated LMTs in 115 samples of A. purpuratus collected between November 2013 and March 2015 from 18 production areas distributed along the Peruvian coast. The hepatopancreas, which accumulates most of the toxins in the scallop, was analyzed with liquid chromatography-tandem mass spectrometry to quantify OA in its free form, YTX, AZA-1, and PTX-2. Baseline separation was achieved in 19 min. Linearity (R2 > 0.997), precision (coefficient of variation < 15%), and limits of quantification (0.155 to 0.479 ng/mL) were satisfactory. YTX was found in 72 samples, and PTX-2 was found in 17 samples, but concentrations of both biotoxins were below the regulatory limits. Free OA and AZA-1 were not detected in the scallop samples. This atypical profile (i.e., presence of PTX-2 and absence of OA) may be linked to the presence of the dinoflagellate Dinophysis acuminata. The production of YTX could be associated with the phytoplankton Gonyaulax spinifera and Protoceratium reticulatum. This is the first systematic assessment of the four types of LMTs in shellfish from Peruvian coastal waters. The results suggest low prevalence of LMTs in Peruvian bay scallops but support continued surveillance and analysis of LMTs in Peru.

Host Defense Effectors Expressed by Hemocytes Shape the Bacterial Microbiota From the Scallop Hemolymph.

The interaction between host immune response and the associated microbiota has recently become a fundamental aspect of vertebrate and invertebrate animal health. This interaction allows the specific association of microbial communities, which participate in a variety of processes in the host including protection against pathogens. Marine aquatic invertebrates such as scallops are also colonized by diverse microbial communities. Scallops remain healthy most of the time, and in general, only a few species are fatally affected on adult stage by viral and bacterial pathogens. Still, high mortalities at larval stages are widely reported and they are associated with pathogenic Vibrio. Thus, to give new insights into the interaction between scallop immune response and its associated microbiota, we assessed the involvement of two host antimicrobial effectors in shaping the abundances of bacterial communities present in the scallop Argopecten purpuratus hemolymph. To do this, we first characterized the microbiota composition in the hemolymph from non-stimulated scallops, finding both common and distinct bacterial communities dominated by the Proteobacteria, Spirochaetes and Bacteroidetes phyla. Next, we identified dynamic shifts of certain bacterial communities in the scallop hemolymph along immune response progression, where host antimicrobial effectors were expressed at basal level and early induced after a bacterial challenge. Finally, the transcript silencing of the antimicrobial peptide big defensin ApBD1 and the bactericidal/permeability-increasing protein ApLBP/BPI1 by RNA interference led to an imbalance of target bacterial groups from scallop hemolymph. Specifically, a significant increase in the class Gammaproteobacteria and the proliferation of Vibrio spp. was observed in scallops silenced for each antimicrobial. Overall, our results strongly suggest that scallop antimicrobial peptides and proteins are implicated in the maintenance of microbial homeostasis and are key molecules in orchestrating host-microbiota interactions. This new evidence depicts the delicate balance that exists between the immune response of A. purpuratus and the hemolymph microbiota.

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.