Importance of the marine biodiversity of the Western Indian Ocean

Posted on September, 04 2018

Biodiversity is most simply defined as the variety of plant and animal life in the world or in a particular habitat.
 Human livelihoods, and even industrial production, are also dependent on what are known as ecosystem services or the provision of goods and services within an environment, with the biodiversity as its basis. We thus need to sustainably conserve our biodiversity (including the associated natural resources) to survive, develop and thrive. The shores and coastal waters of the Western Indian Ocean[1] (WIO) are recognized globally for their biological richness, natural beauty and high ecological and socio-economic value. With some of the Indian Ocean’s most diverse coral reefs, mangrove forests, sand dunes and seagrass beds, the region is one of the less ecologically disturbed areas of ocean in the world. Endemism is high, at 22% in the WIO region (as compared to for example 13% in the Red Sea and 6% in the Eastern Indian Ocean). Five of the world’s seven species[2] of marine turtle nest on beaches in the region. The coastal and marine habitats support rich and complex populations of marine species that rely on this diversity for their productivity. The WIO region generates about 4.8 % of the global fish catch, equivalent to about 4.5 million tons of fish per year.

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.
[1] For the Western Indian Ocean (WIO), we refer here to the definition established by the UN Environment Programme / Nairobi Convention. The WIO includes: Comoros, French territories, Kenya, Madagascar, Mauritius, Mozambique, Seychelles, Somalia, South Africa, and Tanzania.
[2] A common definition of species is that of a group of organisms capable of interbreeding and producing fertile offspring of both sexes (except in the case of asexually reproducing species), and separated from other such groups with which interbreeding does not normally happen.
Marine habitat in the Northern Mozambic Channel
© WWF Madagascar