Counting on Corals

Like the canary in the coal mine, the world's corals are an indication of the health of our oceans. New discoveries are helping scientists better understand these vital ecosystems.

Coral reefs are the rain forests of the ocean, supporting an estimated one million marine organisms, not to mention hundreds of local economies fueled by fishing, tourism, and other industries. Yet corals cover barely one tenth of a percent of the oceans, and possibly up to 75 percent of the world's reefs are threatened, the targets of pollution, disease, and rising water temperatures caused by global warming.

Reef assemblage showing coral diversity on a living reef. Photo: Gary Williams, CASIZG
Coral reefs are made up of colonies of tiny animals called polyps and single-celled photosynthetic algae called zooxanthellae. Photo: Gary Williams, CASIZG

But scientists are uncovering the mysteries of corals to preserve them before it's too late. This June, scientists reported in the journal Nature that "bleaching," when corals expel the photosynthetic algae that color their tissues and provide them with energy-previously thought to be a sign of coral death due to changing water conditions-is actually a survival strategy. By evicting their algal partners, corals enable other algae better equipped to survive in the new conditions to move in. This ensures their long-term survival, but at a dangerous short-term risk-the corals will die if new symbionts don't fill the vacancy.

Scientists have also discovered that reefs provide hidden habitat for hundreds of animals (Nature, October 2001). Weaving a tiny camera into reefs in the Red Sea, researchers counted 370 different animals, many new to science.

Close-up of the polyps that make up a coral colony. Photo: Gary Williams, CASIZG