AN ESTUARINE BENTHIC INDEX OF BIOTIC INTEGRITY (B-IBI) FOR CHESAPEAKEBAY

A multimetric benthic index of biotic integrity (B-IBI) was developed using data from five Chesapeake Bay sampling programs conducted betwee n 1972 and 1991. Attributes of the index were selected by comparing th e response of 17 candidate measures of benthic condition (metrics) bet ween a set of minimally affected reference sites and at all other site s for which data were available. This procedure was conducted independ ently for each of seven habitats defined by salinity and substrate. Fi fteen of the 17 candidate metrics differed significantly between refer ence sites and other sites for at least one habitat. No metric differe d significantly in all seven habitats; however, four metrics, species diversity, abundance, biomass, and percent of abundance as pollution-i ndicative taxa, differed in six habitats. The index was calculated by scoring each selected metric as 5, 3, or 1 depending on whether its va lue at a site approximated, deviated slightly from, or deviated greatl y from conditions at the best reference sites. Validation based on ind ependent data collected between 1992 and 1994 indicated that the index correctly distinguished stressed sites from reference sites 93% of th e time, with the highest validation rates occurring in high salinity h abitats.