Oceans are an integral part of the global carbon cycle, and have absorbed roughly 30% of anthropogenic carbon dioxide emissions since the beginning of the Industrial Era. Data published in 2007 by the Intergovernmental Panel on Climate Change indicate a doubling of atmospheric carbon dioxide by the year 2100, which is projected to decrease average seawater pH by 0.3 – 0.4 pH units. The ramifications of ocean acidification are potentially enormous. A shift in the speciation of dissolved inorganic carbon may affect the degree and distribution of primary production in the worldÍs oceans, while differential organismal responses to decreased seawater pH may spur changes in the species composition of marine phytoplankton. æMy research focuses on the intrinsic organismal and environmental factors that may influence the future timing, duration, and severity of harmful algal blooms caused by toxin-producing dinoflagellates in the Gulf of Maine. This incredibly productive area has historically supported a diverse abundance of marine biomass and an extensive coastal economy. Seasonal blooms of harmful algae, which represent a serious threat to human health and public safety, have been increasing in severity in the GOM since 1972. Ocean acidification may aggravate these blooms by interacting with changes in other oceanographic parameters and anthropogenic hazards to incite synergistic effects on the population dynamics of bloom-forming species. I am principally interested in evaluating the response of the toxic dinoflagellate, Alexandrium fundyense, to the projected climatic changes and acidified conditions predicted to occur in the Gulf of Maine during the next century.