Nitrogenous nutrients promote the growth and toxicity of Dinophysis acuminata during estuarine bloom events.

Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome most commonly caused by dinoflagellates within the genus Dinophysis. While blooms of harmful algae have frequently been linked to excessive nutrient loading, Dinophysis is a mixotrophic alga whose growth is typically associated with prey availability. Consequently, field studies of Dinophysis and nutrients have been rare. Here, the temporal dynamics of Dinophysis acuminata 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 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. acuminata abundances were positively dependent on multiple environmental parameters including 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. acuminata 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 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. acuminata populations in coastal zones

Okadaic acid (OA), dinophysistoxins 1 (DTX1) and total pectenotoxins (total PTX) as fg cell^-1 for nutrient amendment experiments conducted using Northport Bay bloom water during 2011.

<p>Bars are means while error bars represent the SD of triplicate bottles. Asterisks indicate treatments that are significantly different from the unamended control. Abbreviations as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124148#pone.0124148.g002" target="_blank">Fig 2</a>.</p

Multiple regression of <i>Dinophysis acuminata</i> abundances and toxin content per <i>Dinophysis</i> cell on environmental variables.

<p>Both models were significant at the <i>p</i><0.001 level.</p><p>Multiple regression of <i>Dinophysis acuminata</i> abundances and toxin content per <i>Dinophysis</i> cell on environmental variables.</p

Chlorophyll <i>a</i>, and mean nutrient concentrations and ratios at the peak of the bloom compared to before and after the peak of the bloom (when cells where present) for Northport Bay 2008–2012.

<p>Values are means with standard errors in parentheses. 2009 was excluded given the low <i>Dinophysis</i> densities. Values that are italicized are those that are significantly different from each other as determined by a t-test.</p><p>Chlorophyll <i>a</i>, and mean nutrient concentrations and ratios at the peak of the bloom compared to before and after the peak of the bloom (when cells where present) for Northport Bay 2008–2012.</p

<i>Dinophysis acuminata</i> densities (cells mL^-1) at the end of nutrient amendment experiments conducted during 2011 using water collected from Meetinghouse Creek, New York.

<p>Bars are means while error bars represent the SD of triplicate bottles. Asterisks indicate treatments that are significantly different from the unamended control. C = Control, B₁₂ = vitamin B₁₂ and B₁ = vitamin B₁.</p

Log <i>Dinophysis acuminata</i> densities (cells L^-1), and the inorganic nutrients, ammonium, nitrate and phosphate (μM) in Northport Bay, NY, USA during 2008–2012.

<p>Points are means while error bars represent the SD of duplicate samples.</p

Chlorophyll <i>a</i> (μg L^-1), inorganic nutrients (ammonium, nitrate, phosphate, silicate), total dissolved and organic nutrients (μM) as well as nutrient ratios over the course of <i>Dinophysis acuminata</i> blooms in Northport Bay from 2008–2012.

<p>Samples were averaged across the respective inclusive dates with standard errors indicated in parentheses.</p><p>Chlorophyll <i>a</i> (μg L^-1), inorganic nutrients (ammonium, nitrate, phosphate, silicate), total dissolved and organic nutrients (μM) as well as nutrient ratios over the course of <i>Dinophysis acuminata</i> blooms in Northport Bay from 2008–2012.</p

Peak <i>Dinophysis acuminata</i> densities and toxin concentrations in two New York estuaries, Northport Bay and Meetinghouse Creek.

<p>n.d. = not detected.</p><p>Peak <i>Dinophysis acuminata</i> densities and toxin concentrations in two New York estuaries, Northport Bay and Meetinghouse Creek.</p

<i>Dinophysis acuminata</i> densities (cells mL^-1) at the end of nutrient amendment experiments conducted during 2008, 2010 and 2011 using water collected from Northport Bay, New York. Bars are means while error bars represent the SD of triplicate bottles.

<p>Asterisks indicate treatments that are significantly different compared to the unamended control. C = Control, N = Nitrate, P = Phosphate, U = Urea, A = Ammonium, G = Glutamine, B₁₂ = vitamin B₁₂, A+ B₁₂ = Ammonium + vitamin B₁₂, STP = high molecular weight sewage treatment plant organic matter.</p

Field sampling (star) and sewage treatment plant outflow (circle) locations in the Northport-Huntington Bay complex and Meetinghouse Creek, New York, USA.

<p>Field sampling (star) and sewage treatment plant outflow (circle) locations in the Northport-Huntington Bay complex and Meetinghouse Creek, New York, USA.</p