Nitrogenous Nutrients Promote the Growth and Toxicity of Dinophysis acuminata during Estuarine Bloom Events

Abstract

Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome mostcommonly caused by dinoflagellates within the genus Dinophysis. While blooms of harmful algae have frequently been linked to excessive nutrient loading, Dinophysis is a mixotrophicalga whose growth is typically associated with prey availability. Consequently, field studies of Dinophysis and nutrients have been rare. Here, the temporal dynamics of Dinophysisacuminata blooms, DSP toxins, and nutrients (nitrate, ammonium, phosphate, silicate, organic compounds) were examined over four years within two New York estuaries (Meeting house Creek and Northport Bay). Further, changes in the abundance and toxicity of D.acuminata were assessed during a series of nutrient amendment experiments performed over a three year period. During the study, Dinophysis acuminata blooms exceeding one million cells L-1 were observed in both estuaries. Highly significant (p<0.001) forward stepwise multivariate regression models of ecosystem observations demonstrated that D. acuminataabundances were positively dependent on multiple environmental parametersincluding ammonium (p = 0.007) while cellular toxin content was positively dependent on ammonium (p = 0.002) but negatively dependent on nitrate (p<0.001). Nitrogen- (N) and phosphorus- (P) containing inorganic and organic nutrients significantly enhanced D. acuminatadensities in nearly all (13 of 14) experiments performed. Ammonium significantly increased cell densities in 10 of 11 experiments, while glutamine significantly enhanced cellular DSP content in 4 of 5 experiments examining this compound. Nutrients may have directly or indirectly enhanced D. acuminata abundances as densities of this mixotroph during experiments were significantly correlated with multiple members of the planktonic community(phytoflagellates and Mesodinium). Collectively, this study demonstrates that nutrient loading and more specifically N-loading promotes the growth and toxicity of D. acuminatapopulations in coastal zones.