Thematic mapping of tropical marine communities (coral reefs, seagrass beds and mangroves) using SPOT data in Guadeloupe Island

• Published in: Oceanologica acta Vol. 24 S; pp. S3 - S16
• Main Authors: Chauvaud, S, Bouchon, C, Maniere, R
• Format: Journal Article
• Language: French
• Published: 01.01.2001
• Subjects: Marine; ASW, Caribbean Sea, Lesser Antilles, Guadeloupe
• ISSN: 0399-1784

In the framework of a comprehensive study of the coastal marine ecosystems of Guadeloupe Island (French West Indies), a remote sensing survey of marine communities was conducted in the Bay of the Grand Cul-de-Sac Marin. Pictures of SPOT satellite were used. At first sight, XS data from SPOT did not seem to be well adapted to extract information from deepest underwater areas. In the present study, a method for analysis of XS data was developed, which increases tenuous spectral differences associated to very low intensity signals. This technique led to a better distinction of objects, even the deepest ones. Reference surfaces were then identified in the field and a reliable supervised classification was conducted, which reflected the high diversity of ecological themes (up to 32) of the area to 20 m depth. A total of 23700 ha of biota was clearly identified. Mangrove covered up to 2700 ha. Submerged areas were constituted of 15700 ha of soft bottoms and 3800 ha of hard substrate bottoms. On the coral reefs, flourishing coral communities accounted only for 113 ha (11.2%). This result enhances the alarming situation of these communities in Guadeloupe. Finally, seagrass beds took up to 8200 ha (i.e. 42% of the total sublittoral area, 58% of soft bottom substrates). This ecosystem revealed to be of primary importance within the studied area and particular attention was paid to seagrass beds of Thalassia testudinum. Twelve themes were retained to describe them, based on the coverage rate of the substratum by the plants and the type of the sediment colonised. The final document expresses well the high complexity of the studied area. This map constitutes a reference of the present status of the coastal benthic communities of the `Grand Cul-de-Sac Marin' and can be useful for scientists and the administrative managers of that area.Original Abstract: Dans le cadre d'une etude des ecosystemes marins cotiers de l'ile de la Guadeloupe, un inventaire des biocenoses marines de la baie du Grand Cul-de-Sac Marin a ete realise. Dans les Antilles, ces biocenoses sont souvent intriquees de facon complexe, ce qui rend leur cartographie difficile. Les techniques de teledetection spatiale et aeroportee peuvent apporter des solutions a ce probleme. Dans le present travail, une methode d'analyse des donnees XS du satellite SPOT a ete mise au point pour ameliorer nettement la discrimination des objets, meme profonds, en amplifiant des differences spectrales minimes associees a un signal de tres faible intensite. Des surfaces de reference sont delimitees en vue de construire une classification supervisee; 32 themes sont identifies sur une superficie de 23700 ha, jusqu'a l'isobathe 20 m. La mangrove occupe 2700 ha et les surfaces immergees incluent 3800 ha de fonds durs et 15700 ha de fonds meubles. Sur les recifs, les communautes coralliennes florissantes ne representent que 113 ha, soit 11,2% de la surface des recifs cartographies. Ce resultat met en evidence l'etat alarmant des recifs coralliens en Guadeloupe. Sur les fonds sedimentaires, une attention speciale est accordee aux herbiers de phanerogames marines qui constituent un facies particulier occupant 8200 ha, soit 42% des biocenoses infralittorales cartographiees et 58% des fonds meubles. Leur description fait l'objet de 12 themes, differencies sur la base du taux de recouvrement des fonds par les phanerogames et du type de sediment colonise par ces plantes. La methode d'inventaire cartographique (analyse de donnees SPOT) revele la grande complexite de la zone d'etude. La carte produite constitue un outil de reference a la disposition des scientifiques et des gestionnaires de cet espace.