Statistical verification of the Chesapeake Bay benthic index of biotic integrity

The benthic index of biotic integrity (B-IBI) developed for the Chesapeake Bay was statistically verified using simulations and a suite of multivariate statistical techniques. The B-IBI uses a simple scoring system for benthic community metrics to assess benthic community health and to infer environmental quality of benthic habitats in the Bay. Overall, the B-IBI was verified as being sensitive, stable, robust and statistically sound. Classification effectiveness of the B-IBI increased with salinity, from marginal performance for tidal freshwater ecosystems to excellent results for polyhaline areas. The greater classification uncertainty in low salinity habitats may be due to difficulties in reliably identifying naturally unstressed areas or may be due to regional ecotones created by stress gradients. Pollution-indicative species abundance, pollution-sensitive species abundance, and diversity (Shannon's index) were the most important metrics in discriminating between degraded and non-degraded conditions in the majority of the habitats. Single metrics often performed as well as the multi-metric B-IBI in correctly classifying the relative quality of sites. However, the redundancy in the multi-metric B-IBI provided a stable 'weight of evidence' system which increased confidence in general conclusions. Confidence limits developed for the B-IBI scores were used to distinguish among habitats that were degraded, non-degraded, of intermediate quality, or of indeterminate condition. Copyright (C) 2002 John Wiley Sons, Ltd.