BIODIVERSITY OF CORAL-REEFS - WHAT ARE WE LOSING AND WHY

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, fi sh and other animals and plants. In most taxa, the species diversity o f reef-associated organisms is poorly understood because many of the s pecies have yet to be collected and described. High coral mortality ha s been associated with natural events such as hurricanes, predator out breaks and periods of high temperature, but has also resulted from exc ess 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 increase d temperature stress, and which may also bring increased storm frequen cy and intensity. Although the recent extensive episodes of coral blea ching in the Caribbean and eastern Pacific cannot be causally related to global warming at this time, the close link between bleaching and t emperature 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 thi s is considered part of a natural disturbance cycle, there are indicat ions that altered land use patterns and reduction of predators on this seastar by human activities may have increased the severity of outbre aks. 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 i s the reduction in fish populations from intense overfishing in most r eef areas of the world. Coasts without adequately managed reefs have s uffered intense overfishing for both local and export purposes, to the point where the positive effects of fish on those reefs have been com promised. The combination of these destructive factors has altered ree fs in all localities, and many that were once considered protected by distance and low population density are now being exploited as well. O n the positive side, improved understanding of ecological processes on reefs combined with concerted conservation efforts have managed to pr otect some extensive areas of reef for the future.