Coral Reefs of Southeast Asia: Controls, Patterns, and Human Impacts

The intricate coastline of Southeast Asia, and its many islands and island groups—Indonesia alone has over 17 500 islands—contains 32 per cent (91 700 km2) of the world’s shallow coral reefs (Spalding, Ravilious, and Green 2001). While sedimentary regimes appear to restrict reef development in the East China Sea, the Gulf of Thailand, the South China Sea, and around the island of Borneo, reefs are well developed elsewhere. Fringing reefs characterize island coastlines, and there are also barrier reefs and, in the deeper waters of the South China Sea and to the east, atoll-like reef structures. Although the region has a distinguished history of reef studies—in which the pioneering work of R. B. Seymour Sewell, J. H. F. Umbgrove, and Ph. H. Kuenen on the Snellius expedition (1929–30) come particularly to mind—the lack of detailed information about many areas remains considerable. The coral reefs, and their associated shallow-water ecosystems, within this region are the product of both historical and contemporary processes. A wide range of hypotheses to explain coral distributions have been proposed. These include the importance of the widespread availability of suitable shallow substrates for coral growth with submergence histories determined by regional tectonic and sea-level dynamics (e.g. Hall and Holloway 1998), the variety of habitats present (e.g. Wallace and Wolstenholme 1998), and the more contemporary roles of high sea-surface temperatures and ocean current circulation patterns, including the dynamics of western Pacific Ocean–eastern Indian Ocean connectivity (Tomascik et al. 1997a). Both sets of controls show wide variation across the region. Thus, for example, geological settings range from tectonically stable platforms to rapidly uplifting plate collision zones of considerable seismic and volcanic activity. Present-day environments vary from equable, tranquil interior seas to cycloneand swell wave-dominated environments on the region’s margins. Added to these controls are the perturbations introduced by, for example, periodic coral bleaching and biological catastrophes (e.g. Crown of Thorns starfish infestations; Lane 1996). Taken as a whole, therefore, the coral reefs of Southeast Asia demonstrate enormous complexity and considerable dynamism. These reef resources are, however, under considerable pressure from large, and growing, populations and economic development.