Biodiversity of Coral Reefs: What are We Losing and Why?

SYNOPSIS. Coral reefs are threatened by numerous anthropogenic impacts, some of which have already had major effects worldwide. These unique tropical environments harbor a high diversity of corals, reef invertebrates, fish and other animals and plants. In most taxa, the species diversity of reef-associated organisms is poorly understood because many of the species have yet to be collected and described. High coral mortality has been associated with natural events such as hurricanes, predator outbreaks and periods of high temperature, but has also resulted from excess nutrients in sewage and from specific pollutants. Reef corals and associated organisms are also threatened by the possibility of global warming which will result in rising sea levels and periods of increased temperature stress, and which may also bring increased storm frequency and intensity. Although the recent extensive episodes of coral bleaching in the Caribbean and eastern Pacific cannot be causally related to global warming at this time, the close link between bleaching and temperature suggests that global warming will result in severe changes in coral assemblages. Major reef destruction has followed outbreaks of the predatory seastar Acanthaster planci in the Pacific. Although this is considered part of a natural disturbance cycle, there are indications that altered land use patterns and reduction of predators on this seastar by human activities may have increased the severity of outbreaks. Recreational and commercial use of reefs has also increased, and has caused extensive damage, especially near areas of high population density. One of the most obvious and widespread losses to reef biota is the reduction in fish populations from intense overfishing in most reef areas of the world. Coasts without adequately managed reefs have suffered intense overfishing for both local and export purposes, to the point where the positive effects of fish on those reefs have been compromised. The combination of these destructive factors has altered reefs in all localities, and many that were once considered protected by distance and low population density are now being exploited as well. On the positive side, improved understanding of ecological processes on reefs combined with concerted conservation efforts have managed to protect some extensive areas of reef for the future.