Clearance rates and diarrhetic shellfish toxin accumulation by North Atlantic bivalves fed on North American strains of Dinophysis acuminata

Filter feeding bivalves exposed to the harmful algal bloom (HAB) genus, Dinophysis, become intoxicated by the uptake of diarrhetic shellfish toxins (DSTs) produced by these phytoplankton. Here, three species of bivalve (Crassostrea virginica, Mercenaria mercenaria, and Mytilus edulis) native to the western North Atlantic were exposed to two North American strains of toxigenic Dinophysis acuminata to assess the impacts of cell density, cell density as a fraction of the total plankton community, and differing Dinophysis prey (i.e. strains of the ciliate, Mesodinium rubrum) on bivalve clearance rates. All bivalves cleared D. acuminata faster when the dinoflagellate was offered at moderate densities (10,000 cells L^-1) as compared to high densities (100,000 cells L^-1). C. virginica cleared a more toxic Massachusetts strain of D. acuminata significantly faster than a less toxic New York strain (p < 0.05). When presented with Dinophysis in mixed culture with the non-HAB species, Rhodomonas salina, in varying proportions, C. virginica clearance rates slowed significantly as the relative and absolute abundance of D. acuminata increased (p < 0.05), whereas M. edulis displayed a preference for the algae that was more abundant. While C. virginica and M. edulis cleared R. salina significantly faster than M. mercenaria (p < 0.05), there were no differences in the clearance rates of D. acuminata among bivalves. In an additional experiment where M. edulis was exposed to a constant, density (∼ 15,000 cells L^-1) of D. acuminata for 36 h and then fed a non-toxic food source for 24 h to quantify toxin accumulation and depuration, mussels rapidly accumulated DSTs and pectenotoxins (PTXs) during exposure to Dinophysis but depurated PTXs at a rate 3-14 times faster than DSTs (p = 0.07). Collectively, this study demonstrates that the accumulation of DSTs in bivalves varies as a function of D. acuminata density, species, and strain, and that feeding characteristics of, and toxin dynamics within, M. edulis make it more vulnerable to DST accumulation than C. virginica and a likely DST vector in bloom-prone regions.