PUGET SOUND, WASHINGTON: AN EMERGING HOTSPOT FOR PSEUDO-NITZSCHIA BLOOMS AND DOMOIC ACID TOXIC EVENTS

Brian D. Bill^1,2, William P. Cochlan¹, Vera L. Trainer², Mark L. Wells³, Charles G. Trick⁴, and Barbara M. Hickey⁵

¹Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, CA, 94920-1205
²NOAA, Northwest Fisheries Science Center, Seattle, WA, 98112
³School of Marine Sciences, University of Maine, Orono, ME, 04469-5741
⁴Schulich School of Medicine and Dentistry, University of Western Ontario, London, ONT, N6A 5B7, Canada
⁵School of Oceanography, University of Washington, Seattle, WA, 98195

Pacific Northwest inland embayments with limited direct exchange with oceanic waters contain a number of HAB species, including the Paralytic Shellfish Poisoning (PSP) dinoflagellate genus Alexandrium, the fish-killing raphidophyte Heterosigma akashiwo, and the Amnesic Shellfish Poisoning (ASP) diatom genus Pseudo-nitzschia. While blooms of the toxigenic diatom, Pseudo-nitzschia dominate public and scientific attention in the well-studied coastal systems of western North America (e.g., Monterey Bay, Santa Barbara and San Pedro Channels, Juan de Fuca Eddy), the recent Pseudo-nitzschia blooms observed within the inland waters of Puget Sound, Washington suggest that toxic diatom events are not isolated to these coastal systems. Pseudo-nitzschia have been observed in Puget Sound waters since the 1930's (then identified as belonging to the Nitzschia genus), definitively identified as Pseudo-nitzschia species since 1990 (Horner and Postel, 1993; Trainer et al., 1998), and although the neurotoxin domoic acid (DA) has been detected since 1991, only recently have levels exceeded regulatory limits and led to shellfish harvest closures in 2003 and 2005 (Trainer et al., 2007). Our monitoring efforts within Puget Sound have revealed the ubiquitous presence of Pseudo-nitzchia species, routine detection of DA, as well as adequate macronutrient concentrations and composition to sustain algal blooms, both benign and harmful. Research cruises conducted in June and September 2006 found Pseudo-nitzschia cell concentrations as high as 3.4 x10⁵ cells L^-1, particulate DA concentrations as high as 105.2 pg ml^-1, and surface water concentrations of nitrate, ammonium, and silicic acid were routinely 18-20, 1.4-2.0, and 50 µM, respectively, well above macronutrient concentrations limiting for growth. Following the first closures of shellfish harvesting due to DA in 2003 and 2005, it appears that Puget Sound is becoming increasingly conductive to toxic DA events. Due at least partially to increasing human population densities and their use of the marine resources within Puget Sound (including aquaculture activities), the increased frequency of toxic DA events raises questions regarding their impacts on ecosystem and human health. Future sustained monitoring efforts, and research designed to characterize local nutrient dynamics (both natural and anthropogenic) and phytoplankton ecology, are necessary to ensure that commercial, recreational, and Tribal subsistence fisheries continue to provide safe products for human consumption.

HORNER R.A. AND POSTEL J.R. 1993. Toxic diatoms in western Washington waters (U.S. west coast). Hydrobiologia 269/270: 197-205.

TRAINER V.L., ADAMS N.G., BILL B.D., ANULACION B.F., AND WEKELL J.C. 1998. Concentration and dispersal of a Pseudo-nitzschia bloom in Penn Cove, Washington, USA. Nat. Toxins 6: 113-126.

TRAINER V.L., COCHLAN W.P., ERICKSON A., BILL B.D., COX F.H., BORCHERT J.A., AND LEFEBVRE K.A. 2007. Recent domoic acid closures of shellfish harvest areas in Washington State inland waterways. Harmful Algae 6: 449-459.