Etude de la dynamique de la limite supérieure de l’herbier à Posidonia oceanica le long de quelques plages à Mostaganem

Abstract

Posidonia (Posidonia oceanica) is an endemic and emblematic species of the Mediterranean Sea. It forms underwater meadows that are considered key habitats for preserving the ecological balance of marine and coastal environments. However, these seagrass meadows face major ecological and socio-economic challenges that require knowledge of their spatial distribution and vitality. In this context, the present study aims to analyze the dynamics of the upper limit of Posidonia oceanica seagrass meadows off the beaches of Stidia and Petit Port, using a mixed approach. The methodological approach is based on the use of Google Earth Pro satellite images, their georeferencing and processing using GIS (ArcGIS) to extract and analyze Posidonia oceanica formations. This approach is combined with in situ observations of the vitality of the seagrass bed, using scuba diving, as well as sedimentological analyses in the laboratory, in order to assess the edaphic conditions of the sites. The results obtained show a complex dynamic of the upper limit of the seagrass meadows, with signs of both stability and degradation, linked to the presence of continuous and reef-like seagrass meadows on the one hand, and fragmented, tiger-striped seagrass meadows and degraded mats on the other. Also, the analysis of vitality parameters revealed a generally moderate vitality status for both sites.