Western Indian Ocean coral communities: bleaching responses and susceptibility to extinction

A field study of coral bleaching and coral communities was undertaken spanning 8 countries and ~35° of latitude in 2005. This was combined with studies in southern Kenya and northeast Madagascar in 1998 and Mauritius in 2004 to develop a synoptic analysis of coral community structure, bleaching response, susceptibility of the communities to bleaching, and the relative risk of extinctions in western Indian Ocean coral reefs. Cluster analysis identified 8 distinct coral communities among the 91 sites sampled, with 2 distinct communities in northern South Africa and central Mozambique, a third in the central atolls of the Maldives, and 5 less differentiated groups, in a swath from southern Kenya to Mauritius, including Tanzania, the granitic islands of the Seychelles, northeast Madagascar, and Réunion. MassivePorites,Pavona, andPocilloporadominated the central and northern Indian Ocean sites and, from historical records, replaced dominance byAcroporaandMontipora. From southern Kenya to Mauritius, coral communities were less disturbed, withAcroporaandMontiporadominating, and a mix of subdominants including branchingPorites,Fungia,Galaxea, massivePorites,Pocillopora, andSynarea. The survey identified an area from southernmost Kenya to Tanzania as having the least disturbed and highest diversity reefs, and as being a regional priority for management. Taxa vulnerable to future extinction based on their response to warm water, population density, and commonness include largely low-diversity genera with narrow environmental ranges, such asGyrosmilia interrupta,Plesiastrea versipora,Plerogyra sinuosa, andPhysogyra lichtensteini.