BLOOM DYNAMICS OF TOXIC ALEXANDRIUM SPECIES IN THE NORTHEASTERN US

Coastal waters of the northeastern U.S. are subject to recurrent outbr eaks of paralytic shellfish poisoning (PSP) caused by toxic dinoflagel lates in the genus Alexandrium PSP is not uniform across the large reg ion, but instead reflects Alexandrium growth and toxin accumulation in five separate habitats or zones defined by circulation patterns and t he discontinuous distribution of the dinoflagellates. Each of these ha bitats has a unique set of environmental and oceanographic forcings th at determine the timing and extent of bloom development and transport and that regulate the extent of genetic exchange with adjacent populat ions. Several habitats (e.g. the southwestern Gulf of Maine, Massachus etts Bay, and Georges Bank) are linked hydrographically and may share the same Alexandrium population via large-scale transport in a coastal current, whereas the other two habitats (eastern Maine and southern s alt ponds-embayments) seem to be isolated and have little or no hydrog raphic or genetic linkage to adjacent regions during bloom seasons. My paper provides an overview of the regional ecology and oceanography o f Alexandrium through a focus on these five subpopulations. Issues tha t relate to PSP and Alexandrium dynamics throughout the world are high lighted, including species dispersal, the role of cysts and ''initiati on zones'' in bloom development, and the influence of large-and small- scale hydrography on population development and transport. The ability of Alexandrium to colonize multiple habitats and to persist over a la rge region is emphasized in recognition of the adaptability and resili ence of this important organism.