Gulf of Maine Alexandrium fundyense Model Results – 2006

Ruoying He, Dennis McGillicuddy, Don Anderson, Bruce Keafer

Woods Hole Oceanographic Institution

Disclaimer: these simulations are for experimental purposes only.

Results here represent model solutions initiated from a cyst abundance map from late 2005, with germination, growth, and transport of Alexandrium fundyense cells driven by the factors listed below. Note that as the time progresses, there is insufficient cell abundance data over a large area to be assimilated into this model to update it and improve its accuracy.  In the future, we hope to obtain such cell abundance information from the integrated ocean observing system, but that capability is a decade away.

Physical circulation model

Multiple nested ROMS, ca. ~1km resolution in GOM

Tides (M2, S2, N2, K2, K1, O1, Q1)

6-hourly wind and heat fluxes from NOAA/NCEP EDAS (40-km resolution)

River runoff data from USGS

Sea surface temperature from satellites

Initial conditions and open boundary conditions from large-scale parent model (HYCOM)

Alexandrium fundyense model

Population dynamics from Stock et al. 2005; McGillicuddy et al. 2005

Cyst map from NOAA/EPA Fall 2005 Surveys (http://www.whoi.edu/mr/pr.do?id=11987)

Solar radiation from NOAA/NCEP EDAS

Climatological nutrient fields from BIO (Petrie et al., 2000)

New Improvement- The mortality rate of A. fundyense is now parameterized using the temperature dependent Q₁₀ formulation (Durbin and Durbin, 1992)

Observations

R/V Tioga Surveys

http://science.whoi.edu/users/olga/alex_surveys_2006/WHOI_Alexandrium_Surveys_2006.html

Modeled A. fundyense bloom

An animation showing surface wind fields and modeled bloom conditions from March 6, 2006 to July 7, 2006

http://science.whoi.edu/users/ruoying/Redtide_06/movie.html

Model-data comparison

11-12 April: Simulation indicates a swath of low concentration Alexandrium fundyense cells extending from the Bay of Fundy to mid-coast Maine; a broader area of cells is located offshore of Casco Bay, slightly downstream of the WGOM cyst bed.  The simulated bloom has not yet penetrated into Mass/Cape Cod Bays.  The distribution has broadened in the offshore direction, as might occur after upwelling-favorable conditions. Observations from R/V Tioga cruise 171 confirm low cell concentrations in that same area. Note: In this simulation, the highest cell concentrations are in the few hundreds of cells per liter range.  This is at or below levels that would be expected to cause toxicity in shellfish.  The model results are thus generally consistent with shellfish toxicity data from the region – i.e., no toxicity yet in Massachusetts Bay, the north shore of Massachusetts, New Hampshire, or open-coastal areas of western Maine.

25-26 April: Simulated bloom shows widespread by low cell abundance (maximum concentrations of 100-200 cells/L) populations along the coast of western Maine, and some cells have begun to enter Mass Bay; observations from R/V Tioga cruise 177 confirm the presence of cells in the near-shore waters off Cape Ann. At this time, Maine DMR reported “clear ….. signs of low-level PSP in almost all of the areas from the NH border out to Port Clyde” (Darcie Coture e-mail, 4/27). No toxicity had been reported in Mass Bay or the north shore of Massachusetts at this time.

11 May: Simulated bloom shows cells have entered Mass Bay and Nantucket Sound; observations from R/V Tioga cruise 180 confirm the presence of cells in Mass Bay.

17 May: Simulated bloom shows cells in Mass Bay continue developing; observations from R/V Tioga cruise 181 confirm the presence of large abundance of cells in Mass Bay.

25 May: Observations from R/V Tioga cruise indicate that the Alexandrium abundance has reduced relative to last week. The observed highest concentrations of Alexandrium are now primarily located in a patch just off Boston, and that the abundance decreases rapidly offshore. Simulated bloom in Mass Bay agrees well with these observations. The model also shows large blooms in two other areas, one off the east seaboard of Cape Cod, and the other near the coast south of Casco Bay.  

1 June: Observations from R/V Tioga cruise indicate that the Alexandrium abundance continues to decline compared to last week. The observed highest concentrations of Alexandrium are now located in the east entrance of the Cape Cod Canal. Simulated bloom now overpredicts these observations, still showing abundant cell populations in the Mass Bay.   

13 June: Observations from R/V Oceanus cruise reveal the gulf-wide distribution of Alexandrium fundyense. The observed highest concentrations of Alexandrium are now located between Penobscot Bay and Cape Ann. The data also show widespread of Alexandrium population in the Mass Bay. Simulated bloom shows the similar spatial distribution.   

30 June: Observations from R/V Tioga cruise show that areas near the coast within southern Mass Bay and Cape Cod Bay were clear of cells - the same condition also revealed by the model. However, both observation and model indicate cell populations were still abundant along the northern boundary offshore of Cape Ann. The modeled field further suggests some “hot spots” that were near the Penobscot Bay and inside the Bay of Fundy.

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Last update: July 7, 2006