Dead Zones May Threaten Coral Reefs Worldwide
Dead zones affect dozens of coral reefs around the world and threaten hundreds more according to a new study by Smithsonian scientists published in the Proceedings of the National Academy of Sciences. Watching a massive coral reef die-off on the Caribbean coast of Panama, they suspected it was caused by a dead zone—a low-oxygen area that snuffs out marine life—rather than by ocean warming or acidification.
“Ocean warming and acidification are recognized global threats to reefs and require large-scale solutions, whereas the newly recognized threats to coral reefs caused by dead zones are more localized,” said Andrew Altieri, staff scientist at the Smithsonian Tropical Research Institute and first author of the study. “Fortunately dead zones can be reduced by controlling sewage and agricultural runoff into the ocean.”
In September 2010, coral reefs in Almirante Bay, Bocas del Toro Province, showed severe signs of stress. In addition to corals turning white and dying, which is typical during coral bleaching associated with warming events, there were other clues suggesting that more was involved than high temperatures. Many unusual observations pointed to something else as the culprit. There were thick mats of bacterial slime, and the dead bodies of crabs, sea urchins and sponges lay scattered on the ocean floor. Even more odd, there was a clear depth line above which the reefs looked OK, and below which something had gone terribly wrong. Even single colonies of corals that straddled the line were fine above and dying below.
Read more at Smithsonian Tropical Research Institute
Photo: Crabs were flushed from reef crevices by low oxygen conditions but ultimately succumbed to hypoxia. (Photo by Arcadio Castillo)