AMBI AND BENTIX CAN BE APPLIED TO MOLLUSCAN DEATH ASSEMBLAGES TO GUIDE ENVIRONMENTAL MANAGEMENT DECISIONS

AMBI and Bentix are benthic indices that are widely used to guide remediation decisions under two major environmental laws in Europe called the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD). These indices usually incorporate all marine benthic invertebrates in a sample. Some recent studies, however, have applied these benthic indices to only the mollusk species due to the ease of identifying only one taxonomic group to the species level and because molluscan death assemblages may be valuable sources of data for assessing baseline conditions. Although they found that ecological status differences can be detected by applying AMBI and Bentix to mollusks, these studies did not test whether mollusk-only index values, and the ecological statuses indicated by them, are equivalent to those calculated from the whole benthic community. To test this assumption, we performed a meta-analysis of data from 11 European benthic community studies comparing mollusk-only index values with whole-community values. Using five live-dead data sets, we also assessed whether application of AMBI and Bentix to molluscan death assemblages can be used to detect changes in ecological status over time.

We confirmed that the application of AMBI and Bentix to only the molluscan taxa in benthic communities is a viable method for determining the ecological status of water bodies. However, mollusk-only values were not directly comparable to whole-community values. We addressed this issue by calculating regression equations for converting mollusk-only values to estimated whole-community values. Over 70% of the estimated whole-community values indicated the same ecological status as the directly calculated whole-community values. Further, estimated whole-community values calculated using the live-dead data showed differences in ecological status between live and death assemblages. Taken together, these results suggest that AMBI and Bentix calculated from molluscan death assemblages may be useful for establishing baseline conditions, natural range of variation, and trends in ecological status over time. We conclude that mollusk-only benthic index assessments of molluscan death assemblages may be a powerful tool for guiding management decisions under the WFD, MSFD and similar legislation worldwide.