Surface live counts (see map) show that the Alexandrium bloom on Georges Bank have decreased dramatically since the last cruise. The north flank and most of the crest were nearly devoid of cells. A modest tongue of cells (tens to less than 200 cells l-1) emanated from the western side of the northeast peak, extending down the southern flank. The outer edge of the tongue was interrupted by an intrusion of high-salinity slope water. Peak cell concentrations of 224 and 378 cells l-1 were found to the northwest of the slope water intrusion.
These findings are in stark contrast to the results from earlier cruises, during which large areas of the bank were covered by hundreds of cells l-1 in late April / early May (OC445) and thousands of cells l-1 in late May / early June (OC447). The dramatic decrease in Alexandrium abundance from OC447 to EN448 may be associated with a change in plankton community structure. A true-color satellite image provided by Andy Thomas prior to departure suggests the presence of a coccolithophore bloom on Georges Bank and in the adjacent slope waters. Indeed, surface waters had the characteristic “milky green” hue, especially on the southern flank. Microscopic examination of surface samples concentrated by centrifuge confirmed the presence of coccolithophores (Dave Townsend).
Thanks are due to the science party and ship’s crew for a successful voyage. We wish you all a happy and safe 4th of July weekend.
Dennis McGillicuddy, Chief Scientist