The New Nation - Internet Edition

Dipa Paul Chowdhury

Coral reefs are vital to island and coastal communities that rely on them to support the fishing that provides their livelihoods. They are also complex and have the highest biodiversity of any marine ecosystem. They provide important services and direct economic benefits to the large and growing human populations in low-latitude coastal zones.

The natural habitat of coral reefs near the meeting between land, sea, and air can be a stressful environment. Reef organisms have evolved ways to adapt and recover from such stresses over hundreds of millions of years.

However, recent global increases in reef degradation and die-back suggest that both the rate and nature of recent environmental changes are exceeding the capacity of coral reefs to adapt.

This can lead to reefs being displaced by seaweeds and other non reef systems. Such ecosystem shifts are already well advanced in the Caribbean region, where two of the major reef-building coral species have been devastated by disease. In the Indo-Pacific region, repeated episodes of lethal 'bleaching' suggest that reefs cannot recover sufficiently between such events. This crisis is almost certainly the result of interactions between pressure from local human populations and global climatic stresses.

The former includes direct destruction, coastal habitat modification, contamination, over-harvesting, and increased nutrient and sediment build-ups. The latter includes rising ocean temperatures implicated in chronic stress and disease epidemics, as well as mass coral-bleaching episodes and reduction in necessary calcium levels, which provides the building blocks of coral reefs. Increasing atmospheric CO2 levels can also inhibit calcification. These stresses may interact with each other and exacerbate other stresses like disease and predation. As with many ecosystems, it is difficult to separate the effects of global climate and local, non-climate impacts.

Predicting the future of reefs is difficult because current environmental changes are causing a combination of surface ocean chemistry and temperature conditions that have almost certainly never occurred in the evolutionary history of modern coral reef systems.

Key uncertainties include the extent to which human activities will continue to alter the environment; how climate variability such as the frequency and intensity of El Niño Southern Oscillation (ENSO) events will change relative to global temperature; and the biological and ecological responses of coral reef communities to unprecedented future conditions.

Although climate change has the potential to yield some benefits for certain coral species in specific regions, most of the effects of climate change are stressful rather than beneficial.

Continued climate change will almost certainly cause further degradation of coral reefs, which will be even more devastating in combination with the continuing non-climate stresses that will almost certainly increase in magnitude and frequency. Reef systems that are at the crossroads of global climatic and local human stresses will be the most vulnerable.

Research into adaptation and recovery mechanisms and enhanced monitoring of coral reef environments will help us to learn from and influence the course of events rather than simply observe the decline.

A significant step would be an international network of marine-protected areas to provide refuges for future generations of coral reef organisms. Yet, even with such efforts, recent degradation of coral ecosystems combined with future climate change will pose a significant challenge to the global sustainability of coral reefs.