The Réunion island has an exclusive economic zone (EEZ) covering 313 360km2 with marine habitats including coral reefs and seagrass and both rocky and sandy geological formations.
Réunion Island has at least 4,374 types of marine species, including algae, scleractinians, hydrozoans, mollusks (except species of nudibranchs and cephalopods) and large marine species.
In 2004, a total of 885 species of fish living on coral reefs belonging to 150 families have been recorded. Nine fish species can be found only in Réunion, indicating an endemism rate of 1.0%, which are Channomuraena bauchotae, Gorgosia klausewitzi, Neobythites multistriatus, Parupeneus posteli, Upeneus mascariensis, Mimoblennius lineathorax, Cotylo – pus acutipinnis, Oxyurichthys guibei, Pardachirus diringeri and Soleichthys tubifera. The four most important Réunion fish families are: Labridae, Gobiidae, Serranidae, and Pomacentridae.
Highly valued marine species include lobsters and cold-water fish species such as Patagonian tooth-fish. Some pelagic fish species include Albacore tuna, Jacks, Pompanos and Blue Shark.
Recent research by published in the WIO journal of Marine Science in 2018, meanwhile, indicates that 184 species of Echinoderms alone can be found in Réunion’s waters.
Réunion Island has a poorly developed reef system, with 25 km of fringing reef on the west coast of the island. Reef structures in Réunion are divided into coral communities that grow directly on the volcanic rock, reef platforms where the reef flat extends from the shoreline, and fringing reefs (the most mature reefs on the island). Spread over 25 km of the west coast, the corals represent only 8% of the circumference of the island. They are 8,500 years old, with a maximum width of 500 m up to the coral reef. Their depth is shallow, an average of one meter in the area between the barrier and the beach. The reefs alone are home to over 150 species of coral, 2,000 species of mollusks and 900 species of fish. Cetaceans (4 species) are also found in the reef waters of the outer slope.
Mayotte hosts a variety of land and marine tropical ecosystems which are of major ecological value. Landscapes range from tropical forests located on summits and ridges, wetlands amid alluvial plains, bays covered in mangroves, coasts outlined by coral reefs and surrounded by marine flora. Mayotte, a volcanic island more than 8 million years old, shares its flora with Madagascar and, at a regional level, it is considered as one of the world’s 34 biodiversity hotspots.
Due to the subsidence of the island that gradually took place over the past 500,000 years, a large coral reef and lagoon surrounding the island emerged. These are exceptional for their size (1,000 km2) and for the rich biodiversity they host (more than 760 marine fishes (of which 17 are threatened according to IUCN Red List of Threatened Species), 581 marine arthropod species, more than 450 cnidaria and 24 marine mammals).
In the most forested areas, the terrestrial fauna consists of several endemic and threatened species. Notably, Mayotte has recently been recognized as one of the world’s 218 endemic bird areas (more than 130 species recorded (of which 2 are endemic, i.e. the Mayotte Sunbird and the Mayotte Drongo).
The Iles Eparses
The Iles Eparses are among the last sanctuaries of marine and terrestrial tropical biodiversity in the South Western Indian Ocean. Geographic isolation and very limited human occupation historically have largely preserved these territories. The Iles Eparses boast a vast biodiversity resulting from the unique ecosystems consisting mangroves, fossil reefs and pools. The islands are considered to be among the last sanctuaries of terrestrial tropical biodiversity. Besides the healthy reef systems (majorly found in the Glorieuses), each island is an important bird and biodiversity area (IBA) with diverse flora on each island, some of which are endemic. The diverse flora and fauna are a result of the difference in climate.
The Europa Island is a Ramsar site with several plant species and the 2nd biggest regional nesting site for green turtles and endangered birds. The island is the breeding stock of green turtles, which number between 8,000 and 15,000 females. These numbers make Europa the third largest atoll nesting site for green turtles in the world and the largest in the Indian Ocean. Europa’s shark species include the blacktip reef sharks (Carcharhinus melanopterus), lemon sharks (Negaprion acutidens) and shooling hammerhead sharks (Sphyrna mokarran). Europa is home to eight breeding seabird species, including an endemic subspecies of the white-tailed Tropicbird (Phaethon lepturus europae).
Juan de Nova, on the other hand, is an important nesting site for hawksbill turtles; nursery areas for grey reef sharks; largest population of sooty terns in the Indian Ocean and one of the largest in the world with more than 2 million breeding pairs. Within Juan de Nova is also the presence of coconut crab Birgus latro.
Glorieuses has the second largest population of sooty terns, with 760,000 breeding pairs. There’s presence of coconut crab Birgus latro. The other island, Bassas da India offers aggregations of juvenile sharks Carcharhinus galapagensis. Zélée Bank is potentially a nursery ground for grey reef sharks (C. amblyrhynchos) and marine mammals such as the humpback whales that are present during the southern winter to breed and give birth.
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 Wickel, J., Jamon, A., Kiszka, J., Layssac, K., Nicet, J.B., Sauvignet, and H., Seret, B. 2010. Structure des communautés de requins et autres poissons prédateurs des bancs récifaux de Geyser, Zélée et Iris (Canal de Mozambique). Rapport du Groupe de Recherche sur les Requins – Océan Indien (MAYSHARK) pour la Direction de l’Agriculture et de la Forêt de Mayotte.