Luoma, S. USGS, snluoma@usgs.gov
Hornberger, M. USGS, mhornber@usgs.gov
Cain, D. USGS, djcain@usgs.gov
Parchaso, F. USGS, parchaso@usgs.gov
Thompson, J. USGS, jthompso@usgs.gov

 
METAL INFLUENCES ON A CLAM POPULATION: LONG-TERM STUDIES IN SAN FRANCISCO BAY.
 
Metals in sediments and tissues of the bivalve, Macoma balthica, were analyzed monthly between 1975 and 1997 at a mudflat in San Francisco Bay. Annual maximum Cu in clams was >500 ug/g in 1980 and 70 ug/g in 1997. Annual maximum Ag concentrations were >200 ug/g in 1978 and 9 ug/g in 1997. Sediment contamination followed similar trends, but concentrations never exceeded guidelines for sediment quality. No unidirectional trends in sediment characteristics or salinity were observed. Simple long-term trends in condition index of the clams were not evident. Detrended analysis of seasonality showed that weight gain did not occur in the Fall during the period when Cu and Ag exposures were highest, but reappeared after annual maximum Cu and Ag concentrations declined. Ripe or spent gonads cells were rarely present in sections from archived animals when contamination was greatest. Reproductive maturity was rarest in fall and summer until 1989. Skewed gender ratios were also observed in the 1970's. Earlier studies also identified metal-specific signs of stress in the early 1980's. Only the trend in metal contamination co-varied with changes in life history and reproductive capabilities in M. balthica, but the response to metal contamination was complex.
 
Day: Friday, Feb. 5
Time: 04:00 - 04:15pm
Location: Sweeney Center
 
Code: SS28FR0400S