BIOLOGICAL CRITERIA, ENVIRONMENTAL-HEALTH AND ESTUARINE MACROBENTHIC COMMUNITY STRUCTURE

Biological criteria for defining water quality and the presence of acc eptable levels of benthic resources are evaluated for estuarine macrob enthic communities of the lower Chesapeake Bay, USA. Models of expecte d community values as a function of salinity are presented for communi ty biomass, numbers of individuals, species richness, percent biomass of deep-dwelling species, percent biomass of equilibrium species, and percent biomass of opportunistic species. The models presented may ser ve as, or be used to develop, biological criteria for estuaries. Tidal freshwater and oligohaline regions had the highest variability in mod el parameters due to patchily distributed, large-sized bivalve species . In the absence of data from pristine habitats, the models were devel oped from a 5 year data set (1985-1989) for stations considered to be minimally impacted. The models produced were used to evaluate benthic communities of two regions of the Chesapeake Bay-one exposed to summer low dissolved oxygen events (hypoxia/anoxia) and the other characteri zed by sediments contaminated with heavy metals and polynuclear aromat ic hydrocarbons. Stations exposed to stress from either low dissolved oxygen events or contaminated sediments were characterized by 1. reduc ed community biomass, 2. reduced species richness, 3. less biomass con sisting of deep-dwelling species and equilibrium species and 4. more b iomass consisting of opportunistic species. Some unstressed habitats c an be highly dominated by shallow-dwelling long-lived species, thus do minance of deep-dwelling species in biomass must be used with caution as a biological criterion. The number of individuals per m2 was highly variable for some stressed stations and this parameter is probably of limited value as a biological criterion characterizing the quality of estuarine habitats. No single method or analysis is likely to produce stress classifications without unacceptable misclassifications. Ecolo gical stress, from any source, is best measured by multiple methods or analyses with different assumptions. The consistency of classificatio n between different approaches would provide the robustness necessary to judge the reliability of a stress classification.