C.5.2.2 Georges Bank Linkages to the WMCC and EMCC (PIs: O'Reilly, Doucette)

Rationale: The Georges Bank research plan will explore the hypothesis that annual variability in PSP on Georges Bank can be explained by variability in the WMCC and/or EMCC transport of Alexandrium. The objectives are to: 1) ascertain the status of PSP toxins in surfclams and mussels in the shoal water along the northern flank of Georges Bank; 2) characterize the timing of toxification relative to blooms of Alexandrium in other parts of the Gulf; and 3) investigate interannual variability in PSP in the context of time-series changes in circulation inferred from satellite measurements and from circulation models of advective transports in the vicinity of Georges Bank.

Approach: Four sampling sites along the northern series of shoals should provide adequate detection of toxicity for this region (Fig. 5). Shellfish will be collected using a charter vessel at specific sites that match historical sampling (see Fig. 1, White et al., 1993) depending on shellfish availability. Monthly sampling during April, May, June, and July, will provide a high probability of capturing pre-toxicity, toxification, and post-exposure conditions in an economical strategy for evaluating linkages between inshore and Georges Bank PSP events. Since variability in toxin levels among individual bivalves is high, 3 composites of 10 individuals will be analyzed from each site. Mussels depurate PSP toxins faster than surfclams, so they will provide indication of recent toxin exposure while surfclams will provide indication of both recent and residual toxicity. Toxins will be extracted with standard techniques and analyzed with the receptor binding assay of Doucette et al. (in press). Selected samples will also be analyzed using HPLC to reveal the composition of toxins in the shellfish. Changes in the relative abundance of saxitoxin derivatives through time indicate whether the toxin is old, tissue-bound material or is newly ingested (Shumway et al. 1994).

Drifter and satellite data and modeling studies will be used to determine whether toxicity on the Bank can be attributed to remote sources. The Narragansett NMFS remote sensing group will assemble a time series of satellite imagery bracketing the shellfish sampling period to evaluate seasonal and interannual variability in oceanographic features. J. Manning (NMFS, Woods Hole) will apply the Dartmouth College Finite Element Circulation Model (Lynch et al. 1996) to investigate interannual variability of the water advecting around Cape Cod and onto Georges Bank.