Taking the Heat Off Coral

By Phil Berardelli
ScienceNOW Daily News
8 February 2008

Researchers have found a control mechanism in the western Pacific Ocean that seems to be protecting coral reefs from global warming. The discovery is a welcome bit of good news, the scientists say, because it suggests that some of the most diverse ecosystems in the world might not be in as much jeopardy as previously thought.

Over the last 30 years, average ocean temperatures have jumped 0.5 to 0.7 degrees Celsius. One of the adverse consequences of this rise has been a noticeable worsening in the health of ocean coral populations. As the water warms, the colonies of tiny reef-building animals become more vulnerable to coral bleaching. The disease turns the normally colorful coral a ghostly white and has been killing colonies around the globe at an alarming rate (ScienceNOW, 7 May 2007).

But now a U.S. and Australian team has discovered that, in at least one part of the ocean, there are physical forces that act as a kind of thermostat that appears to be curtailing the heating and might protect some fragile reef systems from further damage. In tomorrow's Geophysical Research Letters, the team, led by marine ecologist Joan Kleypas of the National Center for Atmospheric Research in Boulder, Colorado, reports what they found in the Western Pacific Warm Pool--a well-studied region off the northeastern coast of Australia. Temperature readings taken here between 1950 and 2006 show that the water has warmed by less than 0.1%26deg;C, considerably less than other ocean areas studied. Not coincidentally, the team has found much less evidence of coral bleaching in the area, with only four outbreaks in the last 25 years.

One reason why the Western Pacific Warm Pool coral seems healthier, the researchers say, is that the waters there are warmer to begin with--about 29%26deg;C--compared to temperatures in the rest of the ocean. So it's possible that the mitigating effects of the thermostat have created a natural protection against bleaching. Although no one fully understands what powers the thermostat, or whether it will be effective against further warming, Kleypas says it's critical to unravel its mechanism "if we are to understand whether this area will continue to warm less in the future."

Perhaps a bigger question is whether anything learned about the thermostat could help protect coral colonies in more volatile waters, Kleypas says. Failing that, she adds, "since we don't have the resources to protect every coral reef, we might want to ramp up our efforts to conserve reefs that are less vulnerable to bleaching."

The findings should cause neither "despair nor unbridled optimism about the future of coral reefs," says Richard Aronson, senior marine scientist at Dauphin Island Sea Lab in Alabama. The corals in warmer waters do seem to be insulated from the effects of climate change, he says, but only somewhat. Still, the research should at least "compel us to stop wringing our hands about the impending demise of reefs and get the data to be more accurate in our projections," Aronson says.

Related sites

Background on coral bleaching

More on coral bleaching

More on the Western Pacific Warm Pool