CHARACTERISTICS OF THE JUAN DE FUCA EDDY, A SOURCE OF DOMOIC ACID TO THE WASHINGTON COAST

Vera L. Trainer¹, Barbara M. Hickey², Evelyn Lessard², Mark Wells³, Charles Trick⁴, and William P. Cochlan⁵

¹NOAA Fisheries, Marine Biotoxins Program, Northwest Fisheries Science Center, Seattle, WA 98112, USA
²School of Oceanography, University of Washington, Seattle, WA 98195, USA
³School of Marine Sciences, University of Maine, Orono, ME 04469, USA
⁴Schulich School of Medicine, University of Western Ontario, London, Ontario N6A 5B7, Canada
⁵Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, CA 94920, USA

ECOHAB Pacific Northwest cruises off the Washington coast show that the Juan de Fuca eddy, a topographically-trapped seasonal feature is a site where domoic acid can predictably be found during summer months. The highest toxin levels are generally located in the colder water in the eddy and along its edges. The location of toxin-producing Pseudo-nitzschia is similar during each cruise, whereas the specific cellular toxicities varies dramatically among cruises. Although Pseudo-nitzschia are found in the nearshore coastal upwelling zone as well as in the vicinity of the eddy, Pseudo-nitzschia have not been found to be toxic in blooms associated with actively upwelling water. The eddy region has a number of characteristics that differentiate it from the coastal upwelling zone. In particular, particle residence times in the eddy region are several times those in an active upwelling zone. Available iron supplies to phytoplankton in the eddy are limited and result in a specific composite of diatoms and flagellates. The relationship of iron availability to domoic acid production and release in Pseudo-nitzschia cells may, in part, explain the greater toxicity of cells in this region. Also, survey data suggest that the supply of macronutrients to the eddy is much more persistent than to the coastal upwelling zone-- in the latter region nutrient supply is entirely cut off for several days following each reversal from upwelling (high salinity) to downwelling (low salinity) conditions. In contrast to the coastal upwelling zone, the eddy region is supplied by the comparatively constant, nutrient-rich near surface estuarine flow out of the strait.