Is Bleaching Coral's Way of Making the Best of a Bad Situation?

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At an international conference last month in Edinburgh, Scotland, McCulloch noted that the total area of Earth's coral reefs has shrunk by 30 percent in the past three decades. The Caribbean, for example, has lost as much as 90 percent of its reefs.

Encouraging Findings

Recent studies by McCulloch and Baker offer hope that imperiled corals are flexible enough to survive.

In Edinburgh, McCulloch drew on geological records to demonstrate the resilience of coral during periods of significant climate change over the past 500,000 years. According to his data, eras of warm global temperatures—when sea levels rose by as much as 18 feet (6 meters) above today's level—were periods in which reefs flourished rather than suffered.

Explaining the results, McCulloch said rising sea levels provide "space for corals to grow, and warmer ocean temperatures allow expansion of reefs to sub-tropical regions."

Future warming won't necessarily spell the end of reefs, but "it's all a matter of timing," he said. "[Reefs] could do well in a warmer world—as long as the rate of warming is no faster than they can cope with, and assuming that our pollution doesn't kill them off first."

The experiments by Baker, reported in the June 14 issue of the journal Nature, also suggest that coral is remarkably adaptable, thanks in part to its cunning use of algae.

Baker transplanted dozens of coral colonies in the San Blas archipelago of Panama to depths that were shallower or deeper than those in which the corals had naturally developed. The study was designed to simulate the environmental change that stationary reefs would be exposed to as a result of rising or falling sea levels.

Coral colonies at different depths host different types of algae. So Baker monitored the transplanted corals to see whether their algae would survive at the new depths, and whether the coral colonies themselves would ultimately live or die.

The colonies that shed their original algae, he found, were able to attract different species of algae that were more suited to living at the new depths. Of the 11 coral colonies that experienced significant bleaching, none died during a 12-month follow-up period. In comparison, seven colonies that had kept their original algae species after being transplanted eventually died.

Artificially changing the depth at which a coral colony lives is one thing. But it remains unclear whether the adaptive process of bleaching will be enough to save coral reefs bombarded with pollution or slowly roasting in ever-warming waters.

McCulloch said: "We should be refocusing our efforts to reduce the effects of direct human-caused stresses on reefs, rather than be too sidetracked by coral bleaching."

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