Ecosystem health assessment using the Mediterranean seagrass Posidonia oceanica: A review

The endemic Mediterranean seagrass Posidonia oceanica is a key species in coastal waters and it is widely employed as an ideal biological indicator for assessing the quality of water bodies, in accordance to the Water Framework Directive (WFD), as well as for assessing the health status of coastal ecosystems. In this contribution the current situation of the P. oceanica monitoring programs in the Mediterranean Sea is reviewed focusing on those descriptors adopted commonly by researchers and local administrators. The application of recently introduced approaches based on a set of synthetic ecological indices, namely the Conservation Index (CI), the Substitution Index (SI) and the Phase Shift Index (PSI), is also reviewed discussing their effectiveness in the context of ecosystem health assessment and of the requirements of the WFD. The CI, the SI and the PSI go beyond the quality of the water and, thus, the WFD, as they provide additional indications on past events of disturbance that affected a meadow, on potentiality of a meadow to recover, on quality of sediments, on biological pollutants. An integrated approach based on the descriptors of the water quality together with the three ecological indices of the ecosystem health (CI, SI, and PSI) is thus recommended in order to discriminate the main components affecting the status of coastal ecosystems. Application of the CI, the SI and the PSI should be experienced in different areas of the Mediterranean Sea for selecting appropriate reference sites and for formulating more generalized classifications that shift the requirements of the WFD toward the perspective of the ecosystem health evaluation.