Global warming slows coral growth in Red Sea
ScienceDaily (July 16, 2010) — In a pioneering use of computed tomography (CT) scans, scientists at Woods Hole Oceanographic Institution (WHOI) have discovered that carbon dioxide (CO2)-induced global warming is in the process of killing off a major coral species in the Red Sea. As summer sea surface temperatures have remained about 1.5 degrees Celsius above ambient over the last 10 years, growth of the coral, Diploastrea heliopora, has declined by 30% and “could cease growing altogether by 2070” or sooner, they report in the July 16 issue of the journal Science. “The warming in the Red Sea and the resultant decline in the health of this coral is a clear regional impact of global warming,” said Neal E. Cantin, a WHOI postdoctoral investigator and co-lead researcher on the project. In the 1980s, he said, “the average summer [water] temperatures were below 30 degrees Celsius. In 2008 they were approaching 31 degrees.” Cantin and WHOI Research Specialist Anne L. Cohen, the other lead investigator, said the findings were unexpected because D. heliopora did not exhibit one of the typical signs of thermal stress: bleaching. “These corals looked healthy,” said Cohen. But CT scanning of the coral’s skeletal structure in the laboratory revealed “the secrets that the skeletons are hiding,” she said. “The CT scans reveal that these corals have actually been under chronic stress for the last 10 years, and that the rates of growth were the lowest in 2008,” the final year of the study. The other WHOI researchers who participated in the study are climate dynamicist Kristopher B. Karnauskas, coral biologist Ann M. Tarrant and chemical oceanographer Daniel C. McCorkle. … Like MDs diagnosing a sick patient, the researchers scanned six skeletal cores of D. heliopora and were able to pinpoint two high-density growth bands, indicating high thermal stress in 1998 and 2001. This correlates with an abrupt drop in skeletal growth after 1998, which has continued steadily since then. The corals are building skeleton, or calcifying, at a progressively slower rate because they are losing symbiotic algae that live in the coral tissue. By performing photosynthesis, the algae provide the fuel for the corals to make new skeleton. But, says Cohen, “when the corals are thermally stressed, they lose algae and many will eventually starve and die. When corals lose enough algae, they actually turn white, and that’s what bleaching is. We think these corals are on their way to bleaching.” It was the CT technique that enabled early detection of the problem. “The corals look healthy, but looking inside at the skeleton gives you an idea of things to come,” she said. “It’s like osteoporosis. You look at a person and, on the outside, everything seems fine, but inside there are signs of trouble. …
