World seas : an environmental evaluation. Vol. II : the Indian Ocean to the Pacific

Abstract

In the South Indian Ocean, French territories include Reunion (Mascarene archipelago), Mayotte (Comoros archipelago) and the remote Iles Eparses in the Mozambique Channel (Glorieuses, Juan de Nova, Bassas da India, Europa), and Tromelin, North-East of Madagascar. Their coral reefs are varied, from 18 km2 of fringing reefs in Reunion to 1500 km2 of fringing, barrier and double barrier reefs in Mayotte, caye reefs in Glorieuses and Tromelin to atolls in Juan de Nova, Bassas da India and Europa. Pressures on them vary from 850,000 inhabitants in Reunion to no permanent inhabitants in Iles Eparses. Annual monitoring of Reunion and Mayotte shows a gradual decrease in coral cover and fish biomass, due to overfishing. Yet an exceptional biodiversity is recorded in Mayotte, mainly due to its geographical position at the center of the WIO coral triangle, and the variety of reef habitats. In the remote Iles Eparses, more recent monitoring showed a remarkable state of coral reefs and their exceptional fish biomass. These coral reefs are under human threats mainly due to coastal development and land-based pollution, except for Iles Eparses. Climate change has an impact through coral bleaching whose effects are stronger for reefs in the North of the Mozambique Channel. The impact of the 2016 bleaching event was variable on islands but most corals showed signs of resistance with a good recovery of coral colonies. In order to limit degradation and overexploitation of reef resources, national marine protected areas (MPAs) have been made in all French islands: 2007 in Reunion, 2010 in Mayotte, and 2012 in Glorieuses while all Iles Eparses have been under protection for more than 20 years. Despite this, Iles Eparses are beginning to suffer from illegal fishing, including collection of holothurians and perhaps shells, particularly since 2012. Long-term monitoring is essential to describe trends in coral communities in the context of increasing human impact and climate change