Résumé
Since the publication of the handbook for producing coral reef habitat maps (2016) the French overseas territories of the Indian Ocean have launched several programs to produce marine habitat maps on their territory. The maps were produced in Mayotte and Zélée, in the French Eparses Islands in Geyser, Europa, Glorieuses, Juan de Nova and Tromelin and in Reunion. Most of them have been carried out on shallow water (0-30m). Thus, 2249 km² of reef habitats (including the lagoon) were mapped between 2015 and 2023, ie 96% of coral reef. Concerning non-reef habitats like basaltic coasts, present almost exclusively in Reunion, more than half of them have already been mapped and the rest should be published in 2023. These habitat maps were produced from Pleiades satellite images, aerial images (spatial resolution 2m/0.5m) and bathymetry data from aerial Lidar surveys (spatial resolution: 1m) and acoustically data. In Reunion, the mapping of basaltic habitats, not visible on satellite images, was made possible by the use of bathymetric data. The habitat maps were produced by processing images, either by visual clipping, supervised classification or by processing bathymetric data (3D bathymetry, calculation of roughness, slopes, slope variance, etc.). Ground truthing was also carried out in most of the territories (underwater video, visual census in scuba-diving and snorkelling) to describe the dominant benthic communities in order to have a precise description of the communities assemblages corresponding to each island. In addition to habitats and coral cover maps, remarkable habitats (hot spot diversity, geomorphology), and the main substrates characterizing the surface available for the fixation of the sessile benthic fauna and flora, are also produced. In parallel with the production of the maps, the National Museum of Natural History and the French Initiative for Coral Reef are producing the typology of habitats for all the territories. The typology of habitats thus created will be referenced at the national level in the Natural Heritage National Inventory. A detailed sheet of each habitat has already been produced (description of the geomorphology, substrate, dominant and characteristic species, sensibility and pressures exerted on the habitats). It will thus be available and will make it possible to harmonize the habitat maps produced, in particular within the framework of the impact study. The maps are essentials for management and used for various purposes, like implementation and boundaries of Natural area of Interest and MPAs, large-scale coral reef health monitoring programs (like bleaching monitoring).