The ECOHAB-GOM program was initiated to address fundamental mechanisms underlying Alexandrium blooms in the Gulf of Maine: 1) the source of the Alexandrium cells that appear in the fresh water plumes in the western Maine coastal current (WMCC); 2) Alexandrium cell distribution and dynamics in the eastern Maine coastal current (EMCC); and 3) linkages among blooms in the WMCC and the EMCC. Utilizing a combination of numerical modeling (highlighted in this presentation), hydrographic, chemical, and biological measurements, moored and drifting current measurements, and satellite imagery, a team of 14 investigators from 9 institutions is attempting to characterize the structure, variability and autecology of the major Alexandrium habitats in the Gulf of Maine.

Intensive, small-scale field surveys in 1998 near the outflow of the Kennebec River, a putative "source region", documented an offshore source of cells, presumably from cysts germinating in deep basins. Model simulations of cyst germination (regulated by temperature, light, and an endogenous clock) were used to provide a time- and space-varying input of cells to the coupled physical/biological model of the coastal current system. "Hind-cast" model simulations are consistent with field observations during two bloom seasons. These simulations also led to the development of a conceptual model of how germinated cells in offshore waters may become entrained into the coastal current. Also in 1998, large-scale surveys between Casco Bay and the Canadian border suggest that Alexandrium dynamics in the EMCC are regulated by nutrient availability and mixing depth (light) in a manner that fosters offshore growth and accumulation. ECOHAB-GOM is thus a combined modeling/observational program following an approach commensurate with the multiple scales and oceanographic complexity of paralytic shellfish poisoning phenomena in the Gulf of Maine. Updates of model and cruise results can be found at: http://crusty.er.usgs.gov/ecohab/.