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A multimetric benthic index of biotic integrity (B-IBI) was developed using data from five Chesapeake Bay sampling programs conducted between 1972 and 1991. Attributes of the index were selected by comparing the response of 17 candidate measures of benthic condition (metrics) between a set of minimally affected reference sites and at all other sites for which data were available. This procedure was conducted independently for each of seven habitats defined by salinity and substrate. Fifteen of the 17 candidate metrics differed significantly between reference sites and other sites for at least one habitat. No metric differed significantly in all seven habitats; however, four metrics, species diversity, abundance, biomass, and percent of abundance aspollution-indicative taxa, differed in six habitats. The index was calculated by scoring each selected metric as 5, 3, or 1 depending on whether its value at a site approximated, deviated slightly from, or deviated greatly from conditions at the best reference sites. Validation based on independent data collected between 1992 and 1994 indicated that the index correctly distinguished stressed sites from reference sites 93% of the time, with the highest validation rates occurringin high salinity habitats. [ABSTRACT FROM AUTHOR]