Palp to gill area ratio of bivalves: A sensitive indicator of elevated suspended solids

Abstract

Abstract Area measurements were made of the gills and labial palps of several freshwater bivalve species from sites with distinctly different suspended solids concentrations. Without exception, the palp to gill area ratio (PA:GA) was markedly higher for populations from sites with high versus low suspended solids concentrations. The average PA:GA (expressed as a percentage) ranged from 9·3 to 11·5 for bivalves from high suspended solids concentration sites and from 2.5 to 4.8 for bivalves from low suspended solids concentration sites. Such interpopulation differences were observed for two introduced species, Dreissena polymorpha and Corbicula fluminea , despite extremely brief residence times in an evolutionary sense. At any particular location, different species of native unionids had similar PA:GA. These results suggest that PA:GA is a sensitive biological indicator of suspended solids concentration, with interpopulation differences probably reflecting ecophenotypic rather than genetic variation.