Climate and Pollution Could Be Causes of Crumbling Coral Reefs
THE headline was startling - ``Coral Bleaching Threatens Oceans, Life.''
This wasn't supermarket-tabloid sensationalism. It appeared recently in EOS, the official weekly of the American Geophysical Union. It was a warning from scientists to other scientists. That gave it punch.
The authors - Alan E. Strong and R.E. Montgomery at the United States Naval Academy in Annapolis, Md. - went on to explain:
``People around the world depend on the resources provided by the ocean to support life. But global-scale damage to the coral reefs, a large and integral part of the ocean environment that supports a variety of sea life, is a frightening prospect that may unfold in the coming years.''
This is only the latest of many expressions of concern for the world's coral reefs.
Over the past decade, coral has suffered extensive damage in many different places such as the Caribbean, the tropical Pacific Ocean, and even along Australia's Great Barrier Reef.
Normally colorful corals have turned white and died. Others have crumbled because they could no longer build strong skeletons. This is in addition to direct damage from careless fishing, tourism, or nearby commercial development.
As the Annapolis researchers note, scientists don't understand what is happening, although they have several suspects.
These include both climate variations and human pollution.
Coral is a joint enterprise between an animal and a plant - the microscopic algae zooxanthella. The coral animal gives the algae nitrogen, phosphorous, and a sturdy home. The algae feeds the animal with carbon compounds and provides the coral color.
It's easy to disrupt the relationship. A few degrees rise above normal water temperature can drive out the algae, thereby bleaching the coral and killing it. Montgomery and Strong have been studying this ``suspect.''
The scientists cite several cases in the Caribbean and elsewhere that show a temperature-bleaching linkage. They urge a coordinated global study to try to verify this effect. It could be another reason for concern about human-made global warming.
But temperature isn't the only likely cause of bleaching. Excessive solar ultraviolet (UV) radiation can also do it, as Daniel F. Gleason and Gerard M. Wellington, biologists at the University of Houston, pointed out last October in the journal Nature. They reported experiments that showed that the extra UV transmitted by unusually clear and calm waters can whiten coral.
Here again, potential climate change might increase this kind of coral stress. Human-induced thinning of the ozone layer that partially blocks solar UV isn't a concern.
That effect is small in the tropics. The Houston biologists note, however, that global warming might cause more frequent occurrences of the clear-water conditions that allow greater UV penetration.
Coral brittleness is another matter. Scientists have long suspected that nitrogen and phosphorous from sewage and farm runoff overfertilize coral and impede skeletal formation.
Now Australia's Great Barrier Reef Marine Park Authority has an experiment under way to study this possibility. Preliminary results suggest that phosphorous does the damage. It may be the pollutant to control.
It's clear that scientists know enough about the coral problem to put together a comprehensive global-research effort, perhaps under United Nations sponsorship.
It's time to move beyond expressions of concern and piecemeal research and find out what exactly is going on with the coral reefs and what, if anything, should be done about it.