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June 4, 2008 - Oceanus Update

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Alexandrium surface live counts. R/V Oceanus 447, Center for Coastal Studies, MWRA/Battelle, May 27 - June 4, 2008
(D. Anderson & D. McGillicuddy laboratories, Woods Hole Oceanographic Institution)

Upon completion of the western Gulf of Maine (GOM) survey, we turned our attention to Georges Bank and southern New England (see map).

 Surface underway counts across the gulf in between the two regions yielded mostly zeros, as did most of the cross-bank section on the northeast peak of Georges Bank.  The remainder of the bank was almost completely covered by cell concentrations ranging from a few hundreds to a few thousands of cells l-1.  Concentrations on the central part of the crest were generally lower than the surrounding waters, with cell counts of ca. 200 cells l-1 or less.  Highest concentrations were observed on the southern and southwestern parts of the bank, with the peak concentration reaching 3626 cells l-1.  Surprisingly, cell concentrations in excess of 1000 cells l-1 extended all the way out to the shelf break in some cases.  A set of six stations offshore of the 300m isobath were occupied in an attempt to delimit the southern extent of the bloom; even these showed cell counts of several hundred to nearly 1000 cells l-1.

 The Georges Bank survey was integrated into the WGOM survey through additional stations east of Cape Cod occupied by the Center for Coastal Studies, in addition to two sections across the Great South Channel occupied by Oceanus.  A tongue of several hundred cells per liter extends down the back side of Cape Cod, into the Great South Channel, and appears contiguous with the mass of thousands of cells l-1 on the southwestern part of Georges Bank.

Transects on the continental shelf of southern New England suggest the Georges Bank population is being swept westward by the prevailing flow.   The Nantucket Shoals line was populated by several hundred to nearly 1000 cells l-1.  Cell counts diminished considerably on the Martha's Vineyard line, with only the most offshore station exceeding the 100 cell l-1 mark.

We will make port in Woods Hole at ca. 0830 Wednesday.  I'd like to sign off with a hearty thanks to the science party and ship's crew of OC447, all those involved in the collection and processing of cell counts in the Center for Coastal Studies transects and the MWRA/Battelle survey of Mass Bay.  We also greatly appreciate the toxicity status reports provided by resource managers through the Northeast PSP listserver.  That information certainly influenced our sampling plan, and is a good reminder of why we are all out here.

Dennis McGillicuddy, Chief Scientist

Last updated: July 1, 2019

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