In general seafood is safe, tasty and nutritious, but there are some naturally occurring toxins that can make seafood dangerous for consumers. One such toxin is domoic acid, a potent neurotoxin produced by microscopic diatoms of the genus Pseudo-nitzschia.

Sea Grant researchers have documented the presence of the potent human toxin domoic acid in sport fish caught from a popular fishing pier in California. The discovery has led to further studies aimed at quantifying the public health risk of eating recreationally caught fish, especially for socioeconomic groups whose seafood consumption and culinary practicesmay put them at greater risk.

The goals of this pilot project were to determine the extent of the public health threat posed by pier anglers’ consumption of self-caught seafood containing domoic acid (DA), and to lay the foundation for further research, education and outreach to address the threat. Year 1 project objectives were to: 1) design, test and initiate an intercept survey of SCW anglers to identify and characterize their seafood consumption patterns; and 2) determine the concentrations of HAB toxins in the species targeted by SCW anglers, while monitoring ambient DA toxins and toxic Pseudo-nitzschia species in the SCW area and at a more open-water site. Year 2 project objectives were to: 1) determine whether a quantitative link exists between toxic phytoplankton in the water and DA contamination of commonly caught fish at the SCW; 2) determine the relationship between SCW anglers’ seafood consumption patterns and their socio-cultural and economic characteristics; 3) identify subpopulations of SCW anglers whose seafood consumption patterns put them at risk for exposure to DA; and 4) work with state agencies and other interested parties to determine how best to export these results to support their efforts to protect public health.

This Sea Grant project focused on domoic acid production by the toxin-producing diatoms (Pseudo-nitzschia australis and P. multisieries) in coastal California waters. There were two major aspects of our work: 1) the development of a laboratory HPLC assay for measuring domoic acid and the tracking of DA in a field mortality event using the HPLC assay, and 2) developing continuous culture facilities and examining the nutrient physiology of Pseudo-nitzschia species.

We examined bacterioplankton abundance and metabolic characteristics in northern San Francisco Bay, California during spring and summer 1996 at three sites: Central Bay, Suisun Bay and the Sacramento River. These sites spanned a salinity gradient from marine to freshwater, and sampling occurred during a period of seasonally declining river flow. The microbial measures included radio-labeled amino acid uptake (L-leucine, L-proline, L-serine), ectoenzyme activity (aminopeptidase and 13-D-glucosidase), and bacterial abundance using lum filters to separate free from particle-associated bacteria. We observed a seasonal decline in all bacterial metabolic measures at all stations, suggesting that a system-wide variable may be important in controlling bacterial activity. One such variable is freshwater flow into the Bay (as a proxy for organic matter flux), which positively covaried with all metabolic measures. We also observed a sharp decline in particle-associated bacteria in Suisun Bay and the Sacramento River between July and August. This may be due to combined effects of declining nutritive value of the aging particles, and increasing grazing pressure by benthic filter feeders. Aminopeptidase activity was positively related to increasing salinity and 13-D-glucosidase was negatively related to increasing salinity, indicating a gradient in the relative quality of organic matter from carbohydrate-rich riverine to protein-rich oceanic materiaL Overall, Suisun Bay had the highest proportion of particle-associated bacteria (avg. 49%), followed by Sacramento River (avg, 36%) and Central Bay (avg. 11%), Particles were the sites of enhanced ectoenzyme activity, but not amino acid incorporation. Therefore bacteria may be actively dissolving the particulate organic matter but their growth rates are not significantly enhanced on particles.