Corals don't only occur in warm, sun-drenched, tropical seas; some species are found at depths of three miles or more in cold, dark waters throughout the world's oceans. Some cold-water coral reefs are home to more than 1,300 species of animals, a diversity rivaling some better known tropical coral reefs. Until now, scientists believed bottom trawling a commercial fishing method in which vessels drag large, heavily weighted nets across the bottom to be the greatest threat to cold-water corals. Now, however, a new study published in Frontiers in Ecology and the Environment suggests that human activities could be threatening cold water reefs in another way.

Lead researcher John Guinotte, a marine biogeographer at Marine Conservation Biology Institute (Bellevue, WA) and colleagues say that increasing amounts of atmospheric carbon dioxide (CO2), driven by the burning of fossil fuels, are dissolving into the oceans, causing them to become slightly more acidic. This change in seawater chemistry could harm deep-sea calcifying animals like corals.

Cold-water corals that make their skeletons from aragonite a form of calcium carbonate (the main component of limestone) are most vulnerable. Cold-water, reef-building corals are prevalent in the North Atlantic, where there is a deep layer of water supersaturated with aragonite. In pre-industrial times, more than 95 percent of cold water reefs around the world were found in waters supersaturated with aragonite. However, this layer of supersaturated water is shrinking as concentrations of CO2 increase.

"Scientists have known for years that shallow-water tropical coral reefs are threatened by both warming oceans and chemical changes in seawater caused by the build-up of CO2 in the atmosphere. Above-average seawater temperatures have caused coral bleaching events throughout the world, and the calcification rates of corals exposed to more acidic conditions in laboratory experiments have shown worrisome
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Contact: Annie Drinkard
annie@esa.org
Ecological Society of America
3-Apr-2006

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