Looking for Lessons in Coral Bleaching

By Jean-Michel Cousteau

This spring, I spent some time in Fiji, and my stay happened to coincide with a major coral bleaching event. At several sites around Fiji, corals and soft corals were pushing out their complement of zooxanthellae, the microscopic algae that reside in their tissues and provide food for the corals and for other reef animals. As any observant diver knows, without the photosynthetic contribution of the algae, the reef turns a deathly white.

Fijian divers first reported stressed corals and soft corals in February. Reports soon multiplied from many different locations as reefs large and small turned white with unprecedented speed. Four months later, the rate of bleaching seemed to be slowing. But while some sites recovered, the event lasted long enough to kill more than 50 percent of the affected corals.

What caused the bleaching in Fiji? Scientific observers suspect warmer-than-normal water temperatures.

Sea surface temperature has been on the rise for decades, paralleling the build-up of atmospheric carbon-dioxide and global warming to give us the warmest climate in 1,200 years. According to the Worldwatch Institute, sea surface temperatures set records in the late 1990s, resulting in large-scale coral losses in all their tropical habitats.

Corals are susceptible to changes in water temperature and quality. How susceptible? When the temperature rises a mere one to two degrees above normal, corals may begin to expel zooxanthellae. A prolonged exposure to temperatures four degrees above normal can result in bleaching and death in up to 95 percent of coral colonies.

Some might say that corals are resilient, having survived periods of glaciation and sea level fluctuation, meteor impacts and other major extinction events in the last 250 million years. But things are different this time. As Chris Bright writes in State of the World 2000, the problem isn't just the size of today's sea surface warming, but its rapidity and extent. It is affecting all coral ecosystems, from Australia to India and from Madagascar to Belize. Many worry that this gives them insufficient time to establish new colonies in more hospitable areas.

Pollution, deforestation and coastal development compound the effects of warm seas. As a result, some scientists estimate that up to 10 percent of the world's reefs are seriously degraded and that another 60 percent face severe degradation within the next 10 to 40 years.

This is not good news for the millions of humans who depend on healthy coral reefs for their livelihoods. From artisanal fishermen to the proprietors of waterfront luxury hotels and the airlines that serve them, the coral reef ecosystem means survival. And by the same token, a dead reef means fewer fish and fewer tourists. Either of these trends would be devastating for a small island nation like Fiji.

What to do?

First, don't panic. Our world is a dynamic place. Corals are routinely ravaged by storms, disease epidemics and starfish booms. But they can recover. Even now, many communities in Fiji are on the mend. The trick to effective management is to know which corals are recovering and why.

Lack of manpower has prevented us from compiling a complete picture of global reef health. But now science appears to be catching up to the needs of conservation.

Remote sensing from aircraft or satellites may allow us to view and assess reefs at a distance. Teams of scientists collaborating with our Ocean Futures researchers are now using hyperspectral imagers and sensors to determine the characteristic "optical signatures" of different coral and algal species and reef communities.

Hyperspectral sensing involves simultaneous measurements of radiation in many narrow spectral bands, usually spanning the complete spectrum from the near ultra-violet through the visible and well into the infrared. High spectral resolution can be linked to high spatial resolution. The goal is to map the ecological structure of coral reefs and provide baseline data that will allow reef managers to detect and monitor environmental changes.

Time is of the essence. But we can't rush science or nature.

Given time, many of the affected corals in Fiji will recover. This is not to imply that we should sit back and accept extinctions as "nature's way." But it does mean that every local bleaching event is not a step toward the imminent and irreversible demise of the planet. Our ability to distinguish between different types of bleaching events will help us design more effective policies for protection.

To be truly responsible stewards of the biosphere, we must be alert to nature's capacity to heal as well as its tendency to suffer.