Quality assessment of Mediterranean and Black Sea transitional waters: comparing responses of benthic biotic indices

1. A large number of ecological indicators have been applied to environmental quality assessment, including taxonomic indices based on one or more biotic elements and eventually environmental variables. Several structural parameters of benthic invertebrate assemblages (i.e. diversity, abundance and proportion of disturbance-sensitive taxa) have been included in the European Water Framework Directive (WFD) to rank the ecological status of the transitional waters. 2. Several macrobenthic biotic indices based on species diversity and sensitivities to anthropogenic disturbance, were proposed as effective tools to answer the requirements of the WFD, however, little is known about the responses of these indices under differing ecological conditions. 3. In the present study patterns of variation of five benthic biotic indices (AMBI, M-AMBI, BENTIX, Engle’s B-IBI, and Paul’s B-IBI) have been compared in eight Mediterranean and Black Sea transitional water ecosystems characterized by different habitat typologies and anthropogenic pressures. 4. Overall, biotic indices provided contrasting responses in terms of environmental quality assessments. Both the Engle and Paul multimetric benthic biotic indices of integrity were developed for North American estuaries and therefore require to be recalibrated for the Mediterranean and Black Sea transitional waters. M-AMBI applied to each habitat typology promises to be more effective, but the high heterogeneity of transitional waters and the lack of reference condition along the European coasts limit its application. Further work is needed to develop a biotic index that provides useful and unambiguous information under different anthropogenic pressures and in different transitional waters.