Clearance rates and toxin accumulation by North Atlantic bivalves during harmful algal blooms caused by the dinoflagellate, Dinophysis acuminata, in NY, USA, estuaries

Diarrhetic shellfish poisoning (DSP) is the intoxication syndrome derived from the consumption of bivalves that have accumulated toxins produced by algae such as Dinophysis acuminata, yet no study has examined the rate at which bivalves feed on this toxigenic species. During 2021 and 2022, the clearance rates (CR) of three commercially significant bivalve species native to the western North Atlantic (Crassostrea virginica, Mercenaria mercenaria, and Mytilus edulis) were quantified during exposure to D. acuminata blooms of varying densities (10² - 10⁵ cells L^-1) at three sites across New York (NY), USA. The same bivalve species were deployed at NY sites experiencing Dinophysis blooms to track accumulation and depuration rates of diarrhetic shellfish toxins (DSTs) and pectenotoxins (PTXs), toxins that are harmful to humans or shellfish, respectively. A native, non-commercial mussel species (Geukensis demissa) was also sampled in situ to quantify toxin accumulation. CR of D. acuminata were greater than chlorophyll-a-based-rates for all bivalves and clearance rates of D. acuminata by C. virginica (1.69 ± 1.34 L h^-1 g^-1) were significantly greater than those of M. edulis (0.46 ± 0.32 L h^-1 g^-1) and M. mercenaria (0.41 ± 0.24 L h^-1 g^-1; p < 0.05). During a bloom event in 2021, C. virginica and M. mercenaria accumulated low levels of pectenotoxin-2 (PTX2), whereas during a more sustained bloom in 2022, C. virginica, M. edulis, and G. demissa accumulated combinations of DSTs (okadaic acid (OA), dinophysistoxin-1 (DTX1)), PTX2, and pectenotoxin-2 seco acid (PTX2sa) with M. edulis DST loads (265 ng OA + DTX1 g^-1 shellfish tissue) exceeding the FDA closure guideline (160 ng toxin g^-1) for three weeks. DST concentrations in M. edulis were significantly higher (p < 0.05) than C. virginica and M. mercenaria, whereas PTX2 concentrations in C. virginica were significantly higher than in all other bivalves (p < 0.05). PTX2sa loads in M. edulis and C. virginica were similar to each other and were significantly greater than PTX2 loads (p < 0.05). Toxin accumulation efficiencies (TAEs) were higher for M. edulis than C. virginica, and TAEs for DSTs were higher than for PTX2 and PTX2sa in both species. The combination of rapid CR of D. acuminata observed in all bivalves, even at >10⁵ cells L^-1, and the ability of bivalves such as M. edulis to rapidly accumulate high levels of DSTs demonstrate these HABs may represent a significant DSP threat in North America.