PARENT SESSION
WP2 Assessing and predicting toxicant effects in an ecologically complex world
3:00 PM to 6:30 PM, Wednesday, 09 May 2001
Session Chair: P. Calow, V. Forbes
Room 2

(369) Assessing toxicant effects in a complex estuary: A case study of silver in San Francisco Bay.

Brown, Cynthia¹, Parchaso, Francis¹, Thompson, Janet ¹, Luoma, Samuel¹, ¹

ABSTRACT- Contaminant exposures in natural systems can be highly variable. This variability can confound determination of contaminant effects. Long term, multi-disciplined studies with high frequency sampling can be effective in overcoming such obstacles. Concentrations of Ag, Cd, Cr, Cu, Ni, V, and Zn in the tissues of the bioindicator clam, Potamocorbula amurensis, are strongly affected by hydrologic variablility (seasonal and interannual) as well as the salinity gradient in the northern reach of San Francisco Bay. An episode of high Ag concentrations (1.08-5.01 g g^-1) was observed mid-gradient in the clams in 1991. High concentrations were not seen in the clams up-estuary (0.71-1.92 g g^-1) from this site, and were reduced down-estuary (0.16-2.67 g g^-1). After 1991, Ag concentrations gradually decreased and were < 1 g g^-1 throughout the year in 1999. Monthly sampling of reproductive status showed a strong seasonal pattern of gamete production in the winter and spring and reduced gamete production in the summer and fall at the stations and the times when highest Ag tissue concentrations occurred (1991-1995). This seasonal pattern changed toward an increase in gamete production throughout the year coincident with the decline of Ag in the clams after 1995. At the highest Ag concentrations, the number of animals that did not successfully produce gametes increased. At moderate Ag concentrations, the period of inactivity after reproduction in spring appeared to be prolonged. Reproductive activity was not impaired during most years at the sites least contaminated with Ag. An annual index of gamete production showed a significant negative correlation with Ag tissue concentrations. No other environmental variables were correlated with reproductive impairment.

Key words: silver, reproduction, Potamocorbula amurensis, San Francisco Bay