MEPS 281:1-12 (2004)  -  doi:10.3354/meps281001

Environmental conditions and phytoplankton dynamics associated with Pseudo-nitzschia abundance and domoic acid in the Juan de Fuca eddy

Adrian Marchetti1,*, Vera L. Trainer2, Paul J. Harrison3

1Department of Botany, University of British Columbia, 6270 University Blvd, Vancouver, British Columbia, V6T 1Z4 Canada 2NOAA Fisheries, Northwest Fisheries Science Center, 2725 Montlake Blvd. East, Seattle, 98112 Washington, USA 3AMCE Program, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, SAR

ABSTRACT: The Juan de Fuca eddy, located off the coasts of Washington (USA) and British Columbia (Canada), has been identified as a region that frequently contains relatively high levels of domoic acid (DA), a toxin produced by some members of the marine diatom genus, Pseudo-nitzschia. This seasonal eddy provides a unique environment to study the influence of nutrients on Pseudo-nitzschia abundance and DA accumulation in the field. Vertical sampling in the Juan de Fuca region was conducted in May, July and September of 2001 in an effort to determine environmental conditions and phytoplankton dynamics within the eddy compared to surrounding waters. The eddy was characterized by high primary productivity and high biomass in May and September relative to surrounding waters and was dominated by diatoms in the >5 µm size-fraction. In May, nitrate (NO3-) concentrations and the corresponding NO3- assimilation rates by phytoplankton within the eddy surface waters were relatively low. In contrast, in September, NO3- was high and NO3- assimilation rates increased by 7 times relative to those in May. DA was below detection levels at all stations in May and July. In September, Pseudo-nitzschia reached highest cell densities (~2 × 104 cells l-1) and particulate DA (~30 ng DA equivalents l-1) was detected in surface waters of the eddy. The presence of DA in healthy growing phytoplankton communities indicates a need to examine other environmental conditions that induce DA production in natural Pseudo-nitzschia populations than have previously been reported in nutrient-stressed laboratory studies.

KEY WORDS: Juan de Fuca eddy · Pseudo-nitzschia · Domoic acid · Nitrate uptake · Carbon uptake · Chlorophyll · Phytoplankton · Biological processes

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