With a view to implementing a sound management of littoral plant formations, and more particularly that of seagrass beds, it would appear of interest to test the not potentiality of image processing for various types of photographs (color, infrared, and black and white). The present study was carried out within the Gulf of St-Florent (Corsica, France) on a Posidonia oceanica reef platform. Over the last 40 years, no major diachronic evolution has been observed within this plant formation. An erosion of the coastline has been noted inland of these seagrass beds, however, with erosion values of up to 40 m. The use of photogrammetric techniques, which are new to the marine environment, allows the possibility of obtaining a numeric model of a given site. The comparison of cartographic and bathymetric data, brought together in a geographic information system, allows the spatial distribution of seagrasses to be evaluated for the first time.