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The diversity, frequency, and scale of human impacts on coral reefs are increasing to the extent that reefs are threatened globally. Projected increases in carbon dioxide and temperature over the next 50 years exceed the conditions under which coral reefs have flourished over the past half-million years. However, reefs will change rather than disappear entirely, with some species already showing far greater tolerance to climate change and coral bleaching than others. International integration of management strategies that support reef resilience need to be vigorously implemented, and complemented by strong policy decisions to reduce the rate of global warming.
Coral reefs are critically important for the ecosystem goods and services they provide to maritime tropical and subtropical nations (1). Yet reefs are in serious decline; an estimated 30% are already severely damaged, and close to 60% may be lost by 2030 (2). There are no pristine reefs left (3-4). Local successes at protecting coral reefs over the past 30 years have failed to reverse regional-scale declines, and global management of reefs must undergo a radical change in emphasis and implementation if it is to make a real difference. Here, we review current knowledge of the status of coral reefs, the human threats to them now and in the near future, and new directions for research in support of management of these vital natural resources.
Until recently, the direct and indirect effects of overfishing and pollution from agriculture and land development have been the major drivers of massive and accelerating decreases in abundance of coral reef species, causing widespread changes in reef ecosystems over the past two centuries (3-5). With increased human populations and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially. For example, markets for fishes and other natural resources have become global, supplying demand for reef resources far removed from their tropical sources (6) (Fig. 1). On many reefs, reduced stocks of herbivorous fishes and added nutrients from land-based activities have caused ecological shifts, from the original dominance by corals to a preponderance of fleshy seaweed (5, 7). Importantly, these changes to reefs, which can often be managed successfully at a local scale, are compounded by the more recent, superimposed impacts of global climate change.
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