Importance of the marine biodiversity of the Western Indian Ocean
The total number of marine species in the WIO region is not precisely known, but the estimated range is between 11 000 and 20 000 or more, with estimates varying depending on the water depth and organism size, mindful that invertebrate fauna in most deep sea environments are the least known. The last census of world’s marine life (2010) resulted in 250 000 species recorded. The main marine biodiversity features of our region are the marine mammals (34 species, particularly the dugong, some species of whale and dolphin), the sharks (ca. 50 species), the rays (30 species), the fishes (ca. over 2,200 species – approximately 75% of world’s coral reef fish species), the turtles (5 species), the sea cucumbers (140 species), the shelled marine molluscs (over 3 200 species, e.g. bivalve, oysters, clams and mussels), the corals (ca. 300 species), the mangroves (9 species), and the seagrasses (12 species).
For comparison, the Coral Triangle area (Indonesia and Philippines areas – 6 countries) comprises the highest coral diversity in the world: around 600 species. Such figure represents 76% of the world’s coral species (798 species). Therefore, the WIO hosts approximately 38% of the world’s coral species, against around 8% of coral species occurring in the Caribbean.
Of these marine species believed to occur in the WIO, 161 are listed as threatened in the IUCN Red List. These may seem low numbers but one must remember that the aforementioned estimate of species believed to occur in the WIO includes undiscovered species; these may already be in jeopardy. The bulk of the species under threat comprise corals (vulnerable due to habitat degradation, disease and exploitation), sea cucumbers (overharvested) and marine mammals, particularly the dugong, some species of whale and dolphin (overharvested and endangered by shipping, fishing nets, etc.), sharks, fish and turtles (many being Endangered or Critically Endangered by fishing).
To end, it is worth to note that the economic value of ocean-related activities (supported by marine biodiversity) in the WIO, the “gross marine product”, is estimated at US$20.8 billion annually. This was calculated in a way that is analogous to the GDP of a country. The gross marine product is equivalent to the 4th largest economy in the region after Tanzania’s and before Mozambique’s.