Cartographie de l’évolution spatio-temporelle de la limite supérieure de l’herbier à Posidonia oceanica et du trait de côte le long de quelques plages à Mostaganem (Algérie).

Abstract

The Posidonia oceanica seagrass meadow is one of the key ecosystems of the Mediterranean Sea, providing numerous ecological functions and ecosystem services, including beach protection against coastal erosion. The regression of Posidonia meadows leads to the loss of these services, making beach erosion inevitable. In order to explore the relationship between the distribution of Posidonia meadows and beach stability, we adopted a methodological approach based on the mapping of Posidonia and the coastline using a geographic information system (GIS). This approach aims to delineate and monitor the evolution of the extent of the meadows in relation to changes in the coastline. The method used relies on GIS and the production of eco-dynamic maps. Through a diachronic approach, we produced maps of the evolution of the upper limit of the Posidonia oceanica meadows and the coastline over a 19-year period, divided into four intervals: 2004-2010, 2010-2016, 2016-2023, and 2004-2023. Additionally, we complemented the cartographic analysis with a study of the sediments from the beach of La Crique to Salamandre, across three stations by site (submarine beach, aerial beach, and coastline) through granulometric analyses, organic matter, and calcimetry. The results regarding the dynamics of Posidonia meadows show a regressive trend across the entire studied area. Significant degradation of the upper limit of the Posidonia oceanica meadow and changes in the coastline were observed between 2016 and 2023. In contrast, relative stability was noted between 2004 and 2010, with slight variation between 2010 and 2016, marked by a minor regression.