Implications of climate change to the Harmful Algal Blooms of the toxic dinoflagellate Alexandrium catenella in the Gulf of Maine.

Gulf of Maine (GoM) surface waters are warming faster than the global average and at an increased rate over the last decade. The region is affected by Harmful Algal Blooms of Alexandrium catenella, but the implications of these rapid changes in temperature on its bloom dynamics have yet to be evaluated. Our goal is to assess the changes in phenology of HABs of A. catenella associated with variations in temperature in the Gulf of Maine. Optimally Interpolated Sea Surface Temperature anomalies (SSTa) from 1985 to 2018 in 3 regions in the GoM (Bay of Fundy, Eastern and Western Maine Coastal Currents) were compared to variations in timing, duration and magnitude of A. catenella cell counts in the Bay of Fundy from a 27 year (1988-2014) time series and to shellfish toxicity data (1985-2005) along the Maine coast. The current average start, peak and end dates of A. catenella blooms in the Bay of Fundy are, respectively, days 166 (mid June), 198 (mid July) and 213 (early August). A significant regression shows warmer SSTa years result in blooms of A. catenella shifting earlier in the year. Projecting SSTa increases to the year of 2050 by the current warming rate of +0.7˚C to +0.5˚C/decade (max/min) (see Thomas et al., this meeting), we can expect the average start, peak and end date of blooms to be as early as days 125/133, 151/160 and 170/178, respectively. If the SSTa and bloom date regression holds true for the Eastern Maine Coast, we could expect blooms to start, on average, in late May (day 143) based on SSTa trends of the region. Other bloom metrics (duration and magnitude) and shellfish toxicity do not have a significant relationship to SSTa. The long-term increase in SST and associated changes in stratification and summer conditions are likely to impact the seasonal dynamics of HABs in the GoM. Shifts in timing of the blooms associated with increased global warming must be taken into account when planning water quality and shellfish closures monitoring strategies.