Investigation of the 2006 Alexandrium fundyense bloom in the Gulf of Maine:In-situ observations and numerical modeling

摘要

In-situ observations and a coupled bio-physical model were used to study the germination, initiation,and development of the Gulf of Maine (GOM) Alexandrium fundyense bloom in 2006. Hydrographicmeasurements and comparisons with GOM climatology indicate that 2006 was a year with normalcoastal water temperature, salinity, current and river runoff conditions. A. fundyense cyst abundance inbottom sediments preceding the 2006 bloom was at a moderate level compared to other recent annualcyst survey data. We used the coupled bio-physical model to hindcast coastal circulation andA. fundyense cell concentrations. Field data including water temperature, salinity, velocity time seriesand surface A. fundyense cell concentration maps were appflied to gauge the model's fidelity. The coupledmodel is capable of reproducing the hydrodynamics and the temporal and spatial distributions ofA. fundyense cell concentration reasonably well. Model hindcast solutions were further used to diagnosephysical and biological factors controlling the bloom dynamics. Surface wind fields modulated thebloom's horizontal and vertical distribution. The initial cyst distribution was found to be the dominantfactor affecting the severity and the interannual variability of the A. fundyense bloom. Initial cystabundance for the 2006 bloom was about 50% of that prior to the 2005 bloom. As the result, the time-averaged gulf-wide cell concentration in 2006 was also only about 60% of that in 2005. In addition,weaker alongshore currents and episodic upwelling-favorable winds in 2006 reduced the spatial extentof the bloom as compared with 2005.