Silver uptake and subsequent effects on growth and species composition in an estuarine community.

Silver within Chesapeake Bay is rapidly taken up by phytoplankton, in accordance with geochemical controls over silver speciation. Phytoplankton accumulate large cellular burdens at non-lethal concentrations, setting up the potential for transfer of silver to herbivores that graze upon the phytoplankton community. However, the American oyster, Crassostrea virginica, does not assimilate silver from phytoplankton, but rather from that dissolved in water. Oysters can accumulate high burdens of silver via this uptake pathway, without apparent effect. There is another, perhaps more significant, mechanism by which silver can impact higher trophic levels. Continuous inputs of low concentrations of silver can cause large changes in species composition and species succession in Chesapeake Bay phytoplankton communities maintained in experimental ecosystems. In addition, oyster growth was reduced significantly relative to growth of oysters of unaltered communities. Such indirect effects of low levels of toxic substances, although difficult to detect, must be considered when assessments of pollutant impacts are made.