Comparative domoic acid kinetics in oysters (Crassostrea virginica) and mussels (Mytilus edulis) feeding on Pseudo-nitzschia multiseries: Implications for species-specific management

Domoic acid (DA), produced by toxigenic diatoms, Pseudo-nitzschia spp., can cause marine faunal mortalities and human illness mainly via consumption of contaminated suspension-feeding bivalves. The capacity to accumulate DA varies greatly among bivalve species, and oysters, Crassostrea spp., have rarely attained unsafe toxin levels during toxic blooms. This study investigates feeding mechanisms and environmental conditions that may explain the differential DA accumulation by oysters, Crassostrea virginica, and mussels, Mytilus edulis, from Pseudo-nitzschia multiseries. Although neither bivalve was negatively affected by DA, ingestion of P. multiseries from monospecific suspensions was limited in oysters by reduced clearance rate (CR) and increased pseudofeces production with increasing cell density. Co-occurrence of flagellates in mixed suspensions enhanced (by 3.4--7.3x) their overall CR, but oysters partially rejected P. multiseries cells in pseudofeces following particle sorting on the gills and palps, as assessed via video endoscopy-assisted sampling. In oysters, selective rejection was enhanced for P. multiseries cells longer than the interplical width (68 mum) of their heterorhabdic gills, whereas the mussels' homorhabdic gills did not permit discrimination between short and long P. multiseries cells. Mussels exhibited 7.4--8.5x higher weight-standardized CRs than oysters, leading to accumulation of 3--7.5x higher weight-specific DA levels from short (24 mum) P. multiseries cells. Inter-specific differences in DA levels were 10x greater in bivalves exposed to long cells (81mum), 3x greater in market-sized individuals compared to juveniles, and are likely to be enhanced <12°C. Uptake and detoxification of DA were faster in smaller oysters but unrelated to body size in mussels. The contribution of viscera to total DA burden remained high (>60%) in mussels throughout uptake and detoxification, but rapidly decreased in oysters. Since detoxification rates were consistently higher in mussels, and both bivalves exhibited comparably low absorption efficiencies on P. multiseries cells, only reduced DA intake can explain the low capacity of C. virginica to accumulate DA relative to M. edulis. Species-specific management of market-sized, DA-contaminated, co-occurring C. virginica and M. edulis stocks may be a viable practice during toxic outbreaks, especially at low water temperatures, and when blooms are largely mono-specific and composed of large-celled Pseudo-nitzschia spp.