Distribution and dynamics of Posidonia oceanica beds along the Alberes coastline

The location and dynamics of Posidonia oceanica beds were studied in the ma rine natural reserve of Cerbere-Banyuls-sur-Mer (eastern Pyrenees, France), through the mapping of bottom assemblages (transects and image processing) and the monitoring of fixed markers installed at the Posidonia oceanica lo wer limit. The surface area occupied by continuous beds is relatively limit ed and localized, whereas the presence of important areas of dead 'matte' w ould seem to indicate that bottom cover by Posidonia oceanica was more exte nsive in the past. Although the limited extension of the seagrass beds seem s to be linked to both a high level of turbidity and severe hydrodynamic co nditions, it is hypothesized that the regressions observed are due to lack of sediment. (C) 2000 Academie de sciences/Editions scientifiques et medica les Elsevier SAS.