NOAA/NCCOS

Under siege.
Along with ocean acidification and rising water temperatures, coral colonies are also threatened by dispersants used to clean up oil spills.

For Coral, a Cure Worse Than the Disease

Researchers have found that the chemicals used to clean up marine oil spills may be much more harmful to the coral than the oil itself. The findings suggest that spill-recovery crews should physically try to contain spills that occur near coral reefs, or allow the oil to degrade naturally, rather than dumping cleanup chemicals in their vicinity.

It's a tough time for the planet's coral. A growing body of evidence shows that the beautiful colonies of tiny anemonelike sea creatures, also called polyps, are suffering from acidification of the oceans, bleaching, and a disease called white syndrome brought about by rising sea temperatures (ScienceNOW, 8 May 2007). Further threats derive from pollution- and sediment-laden freshwater runoff in developed coastal areas, and even direct mining of the coral for building materials.

Researchers at Israel's National Institute of Oceanography in Haifa have uncovered more bad news while investigating oil cleanup chemicals known as dispersants. The chemicals work by breaking up oil slicks into tiny droplets. They are sometimes dumped near coral colonies, many of which are located along the world's coastal areas where oil production and transportation activities are conducted. To test the effect of the dispersants on coral, the team exposed nubbins, or small branch clippings, of two coral species inhabiting the Red Sea--Stylophora pistillata and Pocillopora damicornis--to solutions of six commonly used chemical dispersants for 24 hours and then monitored the nubbins' health for 7 days.

The experiments produced dramatic results: Nearly all of the coral nubbins died after exposure to mixtures of dispersants and oil. Dispersants alone killed up to two-thirds of the coral clippings, whereas oil alone produced no abnormal mortality, the team reports in the 1 August issue of Environmental Science & Technology. The dispersant-oil combination is the most lethal because droplets of oil get pulled farther underwater, where they come into contact with the tiny sea creatures, speculates marine biologist and co-author Baruch Rinkevich. The new findings support banning the use of dispersants near coral reefs, he says.

Marine scientist Richard Aronson of the Dauphin Island Sea Lab in Alabama agrees that more care should now be taken when using dispersants. But that doesn't mean the choice is always straightforward. "Clearly, if you dump oil directly on coral, it could be catastrophic," he says, so there are still situations where using dispersants is the best bet.

Marine biologist John Bruno of the University of North Carolina, Chapel Hill, agrees. "Sooner or later, we are going to see a truly devastating spill hit a coral reef," he says. The question is, "Will the people that decide how to respond take the lessons of this timely study into account?"

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