Development of a new biotic index for ecological status assessment of Italian coastal waters based on coralligenous macroalgal assemblages

Abstract

This paper presents a new biotic index (ESCA, Ecological Status of Coralligenous Assemblages), based on analyses of in situ records of coralligenous macroalgal assemblages in the Mediterranean Sea. The ESCA index was developed on the basis of previous impact evaluation studies carried out by traditional destructive methods. It was validated on an independent dataset collected during a 3-year study carried out at five localities in the north-western Mediterranean, and tested on a gradient of anthropogenic stressors. Assemblage descriptors selected as metrics of the ESCA index were: (a) presence/absence and abundance of sensitive taxa/groups (expressed as sensitivity level of assemblages, SL), (b) diversity of assemblages (expressed as α-diversity) and (c) heterogeneity of assemblages (expressed as β-diversity). The three metrics were combined to give a final value for the multimetric ecological index, Ecological Quality Ratio, calculated as the ratio between the measured values and the value obtained in the reference condition. The Ecological Quality Ratio values ranged from 0 to 1 and five ecological status classes were defined in accordance with the Water Framework Directive. The ESCA index could be used to define the ecological status of the studied sites, providing differences between assemblages similar to those shown by multivariate analyses. Moreover, ecological quality values were quite steady throughout the study period. The ESCA index may represent a useful tool for monitoring programmes in coastal waters, since it has been developed in compliance with the Water Framework Directive; it synthesizes complex information in a simple and reliable way; and its application is simple and cost-effective. However, further studies are necessary to complete index development and to properly evaluate its strengths and weaknesses on a larger scale.

Key words:

• biological index
• coralligenous habitat
• ecological quality status
• macroalgal assemblages
• Mediterranean Sea

Acknowledgements

We are particularly grateful to Carlo Nike Bianchi, Monica Montefalcone and Carla Morri and two anonymous referees whose comments and suggestions have greatly improved the manuscript. We also thank Christine Maggs, Editor-in-Chief, for her support and suggestions in improving the manuscript.