Suppression of the 2010 <i>Alexandrium fundyense</i> bloom by changes in physical, biological, and chemical properties of the Gulf of Maine

Abstract

For the period 2005-2009, the abundance of resting cysts in bottom sediments from the preceding fall was a first-order predictor of the overall severity of spring-summer blooms of <i>Alexandrium fundyense</i> in the western Gulf of Maine and southern New England. Cyst abundance off mid-coast Maine was significantly higher in fall 2009 than it was preceding a major regional bloom in 2005. A seasonal ensemble forecast was computed using a range of forcing conditions for the period 2004-2009, suggesting that a large bloom was likely in the western Gulf of Maine in 2010. This did not materialize, perhaps because environmental conditions in spring-summer 2010 were not favorable for growth of <i>A.fundyense.</i> Water mass anomalies indicate a regional-scale change in circulation with direct influence on <i>A. fundyense</i>'s niche. Specifically, near-surface waters were warmer, fresher, more stratified, and had lower nutrients than during the period of observations used to construct the ensemble forecast. Moreover, a weaker-than-normal coastal current lessened <i>A. fundyense</i> transport into the western Gulf of Maine and Massachusetts Bay. Satellite ocean color observations indicate the 2010 spring phytoplankton bloom was more intense than usual. Early-season nutrient depletion may have caused a temporal mismatch with <i>A. fundyense</i>'s endogenous clock that regulates the timing of cyst germination. These findings highlight the difficulties of ecological forecasting in a changing oceanographic environment, and underscore the need for a sustained observational network to drive such forecasts.