Vera L. Trainer1, Barbara M. Hickey2, and William P. Cochlan3
1NOAA Fisheries, Northwest Fisheries Science Center, Seattle, WA 98112, USA
2School of Oceanography, University of Washington, Seattle, WA 98195, USA
3Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, CA 94920-1205, USA
Algae of the genus Pseudo-nitzschia that can produce the toxin, domoic acid, are frequently observed over the continental shelf off Washington, near the Washington coast and in the Juan de Fuca eddy between Washington and British Columbia. Measurements made during cruises and beach sampling of seawater and shellfish in 1997 and 1998 were consistent with the possibility that domoic acid (DA) from the Juan de Fuca eddy appears to move southward in prolonged upwelling events and then onshore during the first major storm of the fall season, resulting in elevated concentrations of DA in razor clams on coastal beaches. Such events result in immediate closure of coastal clamming beaches, often for the entire season (or longer, due to the slow depuration of DA from razor clam tissue). A new program, ECOHAB Pacific Northwest (PNW), has begun to address the origin of these events by studying the physiology, toxicology, ecology and oceanography of toxic Pseudo-nitzschia species off the Pacific coast of Washington (WA) and British Columbia. During our first two ECOHAB cruises, our objectives were to determine: (1) the distribution of Pseudo-nitzschia spp. in the eddy and coastal upwelling regimes, (2) the production of DA and release by Pseudo-nitzschia in response to environmental conditions, and (3) the potential impact of macronutrient availability on toxin production. We measured both particulate and dissolved levels of DA near the Juan de Fuca eddy and off the Washington coast to determine the spatial distribution of toxin during the early (June) and late (September) upwelling seasons. Low but measurable levels of particulate DA were measured in the eddy, off the central coast near Kalaloch beach, Washington State, and off Barkley Sound, British Columbia, Canada. In early June particulate DA measured less than 30 pM in the eddy region, but increased to a maximum of 500 pM in surface waters after a storm in mid-June. Depth profiles of particulate DA to 50 m indicated that the highest levels were concentrated in the upper 10 m of the water column and at frontal zones near the edge of the eddy.
During the June cruise, the Juan de Fuca eddy was persistent, although its location changed with time. The robust nature of the eddy and of the coastal front was confirmed with surface drifters, whose tracks were very similar to those released much later in the upwelling season and in different years. The transport pathway from the eddy region to the inner shelf and to the shelf from Washington and even to California was confirmed by surface drifters deployed in June in the eddy and even in the strait-those drifters escaped the eddy and traveled south southeast at speeds of 15-20 miles per day. However, during a downwelling event drifters in the water at that time moved onshore toward the WA coast, with one drifter moving to within 7 miles of the beach. Surface fluorescence and satellite imagery during upwelling showed two regions of high values-one southeast of Barkley Sound, the other, adjacent to the Washington coast in the upwelling zone. A region of lower fluorescence emanated from the strait appearing to "wrap around" higher chlorophyll water. Macronutrients were as high at the mouth of the strait as in the upwelling region near the WA coast. These results demonstrate the importance of studying the Juan de Fuca eddy feature in its entirety, as well as coastal regions in both British Columbia and Washington State that are likely impacted by harmful algae originating from this region.