A comparison of mercury contamination in mussel and ammocoete filter feeders

Abstract

The Trinity River, California, has an extensive history of gold and mercury mining, and recent studies demonstrated uptake of legacy mercury contamination by teleost fishes. We investigated mercury concentrations of larval lampreys (ammocoetes; Entosphenus spp.) and western pearlshell mussels (Margaritifera falcata) in the Trinity River to determine whether these two long-lived and sedentary filter feeders show site-specific differences in uptake of this contaminant. We analyzed ammocoetes from four sites in the Trinity River and one reference site in the Mad River for total mercury and mussels from three of the Trinity River sites for total and methyl mercury. We identified longitudinal gradients in ammocoete total mercury levels and methyl mercury in mussels. We found a 70% increase in total mercury in ammocoetes between two of the sample sites, suggesting a potential point source of contamination. Ammocoetes contained levels of mercury 12 to 25 times those of mussels from the same site. Our data indicate that ammocoetes may be a preferred organism to sample for mercury contamination and ecological effects compared with mussels in the Trinity River.