PALP TO GILL AREA RATIO OF BIVALVES - A SENSITIVE INDICATOR OF ELEVATED SUSPENDED-SOLIDS

Area measurements were made of the gills and labial palps of several f reshwater bivalve species from sites with distinctly different suspend ed solids concentrations. Without exception, the palp to gill area rat io (PA:GA) was markedly higher for populations from sites with high ve rsus low suspended solids concentrations. The average PA:GA (expressed as a percentage) ranged from 9.3 to 11.5 for bivalves from high suspe nded solids concentration sites and from 2.5 to 4.8 for bivalves from low suspended solids concentration sites. Such interpopulation differe nces were observed for two introduced species, Dreissena polymorpha an d Corbicula fluminea, despite extremely brief residence times in an ev olutionary sense. At any particular location, different species of nat ive 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.