Physiological and comparative proteomic analyzes reveal immune defense response of the king scallop Pecten maximus in presence of paralytic shellfish toxin (PST) from Alexandrium minutum.

The king scallop, Pecten maximus is a highly valuable seafood in Europe. Over the last few years, its culture has been threatened by toxic microalgae during harmful algal blooms, inducing public health concerns. Indeed, phycotoxins accumulated in bivalves can be harmful for human, especially paralytic shellfish toxins (PST) synthesized by the microalgae Alexandrium minutum. Deleterious effects of these toxic algae on bivalves have also been reported. However, its impact on bivalves such as king scallop is far from being completely understood. This study combined ecophysiological and proteomic analyzes to investigate the early response of juvenile king scallops to a short term exposure to PST producing A. minutum. Our data showed that all along the 2-days exposure to A. minutum, king scallops exhibited transient lower filtration and respiration rates and accumulated PST. Significant inter-individual variability of toxin accumulation potential was observed among individuals. Furthermore, we found that ingestion of toxic algae, correlated to toxin accumulation was driven by two factors: 1/ the time it takes king scallop to recover from filtration inhibition and starts to filtrate again, 2/ the filtration level to which king scallop starts again to filtrate after inhibition. Furthermore, at the end of the 2-day exposure to A. minutum, proteomic analyzes revealed an increase of the killer cell lectin-like receptor B1, involved in adaptative immune response. Proteins involved in detoxification and in metabolism were found in lower amount in A. minutum exposed king scallops. Proteomic data also showed differential accumulation in several structure proteins such as ß-actin, paramyosin and filamin A, suggesting a remodeling of the mantle tissue when king scallops are subjected to an A. minutum exposure.

Dynamic energy budget modeling of Atlantic surfclam, Spisula solidissima, under future ocean acidification and warming.

A dynamic energy budget (DEB) model integrating pCO2 was used to describe ocean acidification (OA) effects on Atlantic surfclam, Spisula solidissima, bioenergetics. Effects of elevated pCO2 on ingestion and somatic maintenance costs were simulated, validated, and adapted in the DEB model based upon growth and biological rates acquired during a 12-week laboratory experiment. Temperature and pCO2 were projected for the next 100 years following the intergovernmental panel on climate change representative concentration pathways scenarios (2.6, 6.0, and 8.5) and used as forcing variables to project surfclam growth and reproduction. End-of-century water warming and acidification conditions resulted in simulated faster growth for young surfclams and more energy allocated to reproduction until the beginning of the 22nd century when a reduction in maximum shell length and energy allocated to reproduction was observed for the RCP 8.5 scenario.

Energetic response of Atlantic surfclam Spisula solidissima to ocean acidification.

In this study, we assessed the Atlantic surfclam (Spisula solidissima) energy budget under different ocean acidification conditions (OA). During 12 weeks, 126 individuals were maintained at three different ρCO2 concentrations. Every two weeks, individuals were sampled for physiological measurements and scope for growth (SFG). In the high ρCO2 treatment, clearance rate decreased and excretion rate increased relative to the low ρCO2 treatment, resulting in reduced SFG. Moreover, oxygen:nitrogen (O:N) excretion ratio dropped, suggesting that a switch in metabolic strategy occurred. The medium ρCO2 treatment had no significant effects upon SFG; however, metabolic loss increased, suggesting a rise in energy expenditure. In addition, a significant increase in food selection efficiency was observed in the medium treatment, which could be a compensatory reaction to the metabolic over-costs. Results showed that surfclams are particularly sensitive to OA; however, the different compensatory mechanisms observed indicate that they are capable of some temporary resilience.

Sources of paralytic shellfish toxin accumulation variability in the Pacific oyster Crassostrea gigas.

This study was designed to assess the contribution of feeding behavior to inter-individual variability of paralytic shellfish toxin (PST) accumulation in the Pacific oyster Crassostrea gigas. For this purpose 42 oysters were exposed for 2 days to non-toxic algae and then for 2 other days to the PST producer Alexandrium minutum. Individual clearance rate (CR) of oysters was continuously monitored over the 4 days using an ecophysiological measurement system. Comparison of CR values when exposed to toxic and non toxic algae allowed to estimate a clearance rate inhibition index (CRII). Toxin concentration of oysters was quantified at the end of the experiment. These data allowed to estimate the toxin accumulation efficiency (TAE) as the ratio of toxin accumulated on toxin consumed. Changes of clearance rate during the experiment indicated that all individuals stopped feeding immediately after being exposed to A. minutum for at least 7 h. This fast response likely corresponded to a behavioral mechanism of avoidance rather to a toxin-induced response. Individuals also showed high inter-variability in their recovery of filtration after this period. Most of the inter-individual variability (78%) in PST accumulation in C. gigas could be explained by the consumption of A. minutum cells, thus emphasizing the importance of the feeding behavior in accumulation. Based on the toxin concentration in their tissues, oysters were clustered in 3 groups showing contrasted patterns of PST accumulation: the high accumulation group was characterized by high feeding rates both on non-toxic and toxic diet and subsequently a low CRII and high TAE. Inversely, the low accumulation group was characterized by low filtration rates, high CRII and low TAE. Both filtration capacity and sensitivity of oysters to toxins may account for the differences in their accumulation. The contribution of TAE in PST accumulation is discussed and might result from differences in assimilation and detoxification abilities among individuals.