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June 23, 2008 - Massachusetts Bay Update

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Alexandrium surface live counts. R/V Tioga, June 16-17, 2008
(WHOI / D. Anderson & D. McGillicuddy laboratories)

The R/V Tioga surveyed the waters of Massachusetts and Cape Cod Bays last week. The Alexandrium live counts indicated that the bloom is ongoing with the highest concentrations observed in Cape Cod Bay. Near the east entrance of the Cape Cod Canal, the maximum concentration was observed at >10,000 cells/L. Incoming surface populations were observed near Cape Ann at relatively low levels (100-300 cells/L). Another patch off of Boston/Scituate was observed at about 1000 cells/L - see map.

Note that most of the cells in the intense patch near the canal entrance were slightly larger, darker and more granular than typical vegetative cells suggesting that the population is now producing a significant number of planozygotes. On Friday June 20, we transited back through that area to redeploy a mooring on southern Stellwagen Bank. As we crossed the area, several samples were collected in Buzzard's Bay to determine if the population was transported through to the west side of the Canal. Less than 20 cells/L were observed at 3 stations in Buzzards Bay. Furthermore, low numbers (<50 cells/L) were also observed on the east side of the canal - the high population observed just offshore of the east entrance to the canal earlier in the week was not found there later in the week. Either that population was below the 1m sampling depth or had been transported out of that area or may have even produced cysts given the observation of planozygotes.

Note also that we cannot provide near real time Alexandrium data at depth, but as the bloom seasonally progresses, we often observe the maximum cell concentration deeper in the water column. At our mooring station on southern Stellwagen Bank, we counted samples at both the surface and 20m depth; the surface concentration was 23 cells/L, while the concentration at 20m was 233 cells/L. This observation indicates that the surface concentrations reported here may be underestimates of the population in the area at this time.

Thanks again to the science party (stalwart Kerry Norton and two summer students in the Anderson lab, Rob Arnold and Shayla Faizan) and the excellent crew of the R/V Tioga.

We're out on the R/V Endeavor sampling near Nantucket Shoals and on Georges Bank later this week and into early July, but plan to add days to the sampling schedule for one more survey in Mass Bay on the R/V Tioga when we return (now scheduled for July 8-10th).

Bruce Keafer, Chief Scientist

Last updated: July 1, 2019

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