Combined synthetic and biotic indices of Posidonia oceanica to qualify the status of coastal ecosystems in the North Aegean

摘要

Mediterranean seagrass Posidonia oceanica is used as a common biological indicator in the monitoring programmes of the Water Framework Directive (WFD) due to its structural and functional features providing information about the status of coastal ecosystems. In this respect synthetic seascape ecological indices using P. oceanica: the Conservation Index (CI), the Substitution Index (SI), the Phase Shift Index (PSI) and the Patchiness Index (PI) provide supplementary data on the meadow status and on the pressures affecting the meadows besides evaluating the water quality. However, these indices have not been adopted by the European Union Water Framework Directive (WFD). This survey is, therefore focused on the qualification of the status of coastal ecosystems in the North Aegean Sea with an integrated approach based on the synthetic (the CI, the SI, the PSI and the PI) and biotic indices (Biotic Index of Posidonia and Ecosystem Based Quality Index) of P. oceanica. Measurements of several parameters are conducted in four sites (2 natural, 2 anthropized) in Gokceada (North Aegean). The preliminary results confirm the efficiency of synthetic and biotic indices to evaluate the ecosystem status in relation with anthropogenic pressures at a local extent. The mean value of the CI corresponds to a "good" status, while the value of the BiPo Index corresponds to a "moderate" and the value of the EBQI corresponds to a "poor" status for Gokceada. Maximum values of the synthetic and biotic indices are recorded in natural sites. On the contrary, minimum values are recorded in anthropized sites close to marine-based activities. In addition, an early stage of a phase shift (PSI 0.25) is recorded due to a low substitution with Caulerpa cylindracea spread around fragmented meadows and dead matte areas. Also, relations (p 0.05) between the scores of the Land Uses Simplified Index (LUSI) and combined synthetic and biotic indices of P. oceanica, verified the negative impacts of anthropogenic pressures on the benthic ecosystems of the North Aegean Sea where the data is deficient.