Corals May Get Help Adapting to Warmer Waters
Monday, February 18, 2008
No one doubts that human-induced climate change has been killing corals across the globe. The question is whether humans can help save them before the devastation is complete.
For decades, rising sea surface temperatures have been driving out and killing the algae, called zooxanthellae, that give reefs their often-spectacular color. That has left behind the lifeless, bleached skeletons built by clustered colonies of thousands of corals. Meanwhile, the oceans' growing acidity, caused by rising levels of carbon dioxide in the water, impedes the biological processes that allow corals to create their limestone structures.
Those changes have devastating effects on the intricate collaboration necessary to build a coral head or reef or fan. That process is the product of a symbiotic marriage between the tiny marine creatures that are corals and even tinier single-cell algae that take up residence in corals and provide them with nutrients as the algae take in energy from the sun and photosynthesize.
A 2004 study estimated that global warming had destroyed 20 percent of the world's reefs since the 1950s. An additional 24 percent are under imminent threat of collapse, and a further 26 percent face eventual destruction. Researchers have found that in seven tropical regions where most coral reefs grow, waters had warmed by 1.3 to 3 degrees over the past century. Though that might not seem like much, a temperature rise of 1.8 to 3.6 degrees above the average high temperature for the summer can trigger bleaching in many reefs.
Since then, however, scientists have learned that some corals seem to resist warming temperatures better than others. Andrew Baker, a University of Miami marine biologist, is about to embark on an experiment aimed at learning whether scientists can help corals adapt by providing them with symbiotic partners better prepared to cope with waters that are growing warmer largely because of the buildup of greenhouse gases from burning fossil fuels.
Some corals have evolved to do this on their own, over a long period of time: Now, researchers want to see if they can speed up the process.
"It's controversial; it's high risk," Baker said last week. "But it's really important we make the effort to try to show not only are we monitoring the situation, but we're trying to do everything we can, literally, to make sure there are as many corals as possible left to save."
Steve Palumbi, a Stanford University marine biology professor, directs a mapping project at his lab to determine where heat-resistant zooxanthellae reside and where they may appear in the years to come. He called Baker's work "essentially one of the first clinical trials for a response to climate change and coral bleaching. We're used to that when it comes to human health, but we're not used to doing it when it comes to the planet's health."
Researchers used to believe there was just one species of zooxanthellae in corals. But since the start of the decade, they have begun to discover that there are more than a dozen, and some have an easier time adapting to rising temperatures than others.
"Not all zooxanthellae are created equal," said Mark Erdmann, a senior adviser to Conservation International's Indonesia marine program. "Previously, they were thought to be the same species everywhere."
Erdmann works in Raja Ampat, a region of Indonesia that boasts 10 times as many hard coral species as the entire Caribbean. By placing temperature-monitoring instruments throughout the area over the past two years, he has found that algae species are thriving in waters from 66.2 to 95 degrees Fahrenheit, depending on the place and time of year. (In Saudi Arabia's waters, corals flourish in nearly 97-degree temperatures.)
The algae that can tolerate the hottest conditions, Erdmann said, "very likely will be crucial to the future survival of the corals in Raja Ampat and in the vicinity." He and his colleagues have identified 15 reef areas that deserve "maximum protection" from overfishing and other pressures, Erdmann said, because they are the ones that are likely to survive in warmer seas.