PSEUDO-NITZSCHIA GROWTH AND TOXIN PRODUCTION IN THE JUAN DE FUCA EDDY IN THE PACIFIC NORTHWEST – ENVIRONMENTAL STIMULATORS OF A TOXIC BLOOM

Charles G. Trick¹, William P. Cochlan², Mark L. Wells³, Vera L. Trainer⁴

¹Schulich School of Medicine and Dentistry, University of Western Ontario, Ontario N6A5B7, Canada
²Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, 94920, USA
³School of Marine Sciences, University of Maine, Orono, ME 04469, USA
⁴NOAA Northwest Fisheries Science Center, Seattle, 98112, USA

As part of the ECOHAB-PNW project to study the community formation, domoic acid (DA) toxicity and transport of Pseudo-nitzschia cells from the shelf waters of Washington State and British Columbia to the shoreline, we examined spatial distribution of key HAB parameters: total phytoplankton biomass, contribution of Pseudo-nitzschia species, and absolute and cell specific DA concentrations. In September 2003 and September 2004, we used deck-board incubation "grow-out" experiments to evaluate if the natural phytoplankton community could be stimulated with modifications of the water chemistry to either increase the biomass further, increase the relative frequency of Pseudo-nitzschia, increase the physiological capacity of the community (P vs. E), or increase the cell-specific or community integrated toxicity due to DA. While there were variations in the community responses to macronutrient additions, cells from several specific water masses responded primarily to nanomolar additions of iron, or to the addition of a nanomolar mixture of iron and copper. We assessed the stimulation of the HAB component of the community physiology by the extent of enhanced growth of Pseudo-nitzschia, the cellular and dissolved levels of DA, the recovery of the photosynthetic capacity of the phytoplankton, and to a less frequent extent, alterations in the buoyancy/sinking trend of the phytoplankton. Yearly variation in the late summer phytoplankton communities indicates that there is a complex regional regulation of phytoplankton community rich in Pseudo-nitzschia, but the commonly implicated macronutrient concentrations are poor predictors of either Pseudo-nitzschia dominance or toxicity. Rather, micronutrient additions of iron and copper stimulated the dominance, toxicity and physiological health in large areas of the Juan de Fuca eddy region and implicate spatial variation in trace metals as the prime proponent of toxicity in these waters.