• Giannasi, Paul
• Nicet, Jean-Benoît
• Rognard, Florian
• Zubia, Mayalen
• Wickel, Julien
• Bigot, Lionel
• Mulochau, Thierry
• Cuvillier, Alexis
• Pinault, Mathieu
• Talec, Pascal
• Mouquet, Pascal
• Andres, Salomé

Abstract

Sincethepublicationofthehandbookforproducingcoralreefhabitatmaps(2016)theFrenchoverseas territoriesoftheIndianOceanhavelaunchedseveralprogramstoproducemarinehabitatmapsontheir territory. The maps were produced in Mayotte and Zélée, in the French Eparses Islands in Geyser, Europa, Glorieuses,JuandeNovaandTromelinandinReunion.Mostofthemhavebeencarriedoutonshallow 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 habitatmapswereproducedfromPleiadessatelliteimages,aerialimages(spatialresolution2m/0.5m)and bathymetrydatafromaerialLidarsurveys(spatialresolution:1m)andacousticallydata.InReunion,the mapping of basaltic habitats, not visible on satellite images, was made possible by the use of bathymetric data.Thehabitatmapswereproducedbyprocessingimages,eitherbyvisualclipping,supervised classificationorbyprocessingbathymetricdata(3Dbathymetry,calculationofroughness,slopes,slope variance, etc.). Ground truthing was also carried out in most of the territories (underwater video, visual census inscuba-divingandsnorkelling)todescribethe dominantbenthiccommunitiesinordertohave aprecise 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 alsoproduced. In parallel with the production of the maps, the National Museum of Natural History and the French Initiative for Coral Reef areproducingthetypologyofhabitatsforalltheterritories.Thetypologyofhabitatsthuscreatedwillbe referenced at the national level in the Natural Heritage National Inventory. A detailed sheet of each habitat hasalreadybeenproduced(descriptionofthegeomorphology,substrate,dominantandcharacteristic 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).

Topics

• surface