Nitrogenous Nutrients Promote the Growth and Toxicity of <i>Dinophysis acuminata</i> during Estuarine Bloom Events

<div><p>Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome most commonly caused by dinoflagellates within the genus <i>Dinophysis</i>. While blooms of harmful algae have frequently been linked to excessive nutrient loading, <i>Dinophysis</i> is a mixotrophic alga whose growth is typically associated with prey availability. Consequently, field studies of <i>Dinophysis</i> and nutrients have been rare. Here, the temporal dynamics of <i>Dinophysis acuminata</i> blooms, DSP toxins, and nutrients (nitrate, ammonium, phosphate, silicate, organic compounds) were examined over four years within two New York estuaries (Meetinghouse Creek and Northport Bay). Further, changes in the abundance and toxicity of <i>D</i>. <i>acuminata</i> were assessed during a series of nutrient amendment experiments performed over a three year period. During the study, <i>Dinophysis acuminata</i> blooms exceeding one million cells L-1 were observed in both estuaries. Highly significant (<i>p</i><0.001) forward stepwise multivariate regression models of ecosystem observations demonstrated that <i>D</i>. <i>acuminata</i> abundances were positively dependent on multiple environmental parameters including ammonium (<i>p</i> = 0.007) while cellular toxin content was positively dependent on ammonium (<i>p</i> = 0.002) but negatively dependent on nitrate (<i>p</i><0.001). Nitrogen- (N) and phosphorus- (P) containing inorganic and organic nutrients significantly enhanced <i>D</i>. <i>acuminata</i> densities 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 <i>D</i>. <i>acuminata</i> abundances as densities of this mixotroph during experiments were significantly correlated with multiple members of the planktonic community (phytoflagellates and <i>Mesodinium</i>). Collectively, this study demonstrates that nutrient loading and more specifically N-loading promotes the growth and toxicity of <i>D</i>. <i>acuminata</i> populations in coastal zones.</p></div>