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Sci Tech
Chemical pollution, sewage could destroy corals
YOU CAN forget global warming as the sole culprit. A combination of humansewage and shipyard discharge may be responsible for the development and
spread of deadly black band disease in corals, researchers at the University of Illinois say.
"Black band disease is characterised by a ring-shaped bacterial mat that migrates across a coral colony, leaving dead tissue in its wake," said UI geologist Bruce Fouke. "Like a rainforest, a coral reef system is a cradle of biodiversity. If we destroy the reefs, we destroy the ocean's ability to reproduce."
To better understand the disease, Fouke and his colleagues - UI microbiologist Abigail Salyers and postdoctoral researchers George Bonheyo and Jorge Frias-Lopez - studied corals off the island of Curacao in the Netherlands Antilles, near the Venezuelan coast.
First, the researchers mapped outbreaks of the disease along the reef. Then they looked for metals such as aluminum, cadmium and zinc that are common pollutants from shipyards and oil refineries.
"The highest number of infected corals, and highest concentration of dissolved metals, occurred near the city of St. Annabaai, which has a major harbour and a large oil refinery," Fouke said. "This suggests that diseased coral may be experiencing increased environmental stress due to pollution, which in turn decreases the coral's resistance to bacterial infection."
Healthy corals contain a natural population of bacteria within a mucous- ich biofilm that provides protection from light, exposure and sedimentation, Fouke said. "Environmental stresses cause corals to secrete more of this mucous to coat their outer tissues. This leads to elevated levels of natural microbial populations, as well as the introduction of ew, potentially harmful bacterial populations."
To identify the microbes inhabiting the black band biomat, the researchers extracted the microbes' DNA, amplified and sequenced it. They found several organisms, including Arcobacter and Campylobacter, which are human pathogens and could be a direct link to raw sewage. Also present in the biomat was a ropy network of cyanobacteria, a unique group of photosynthetic bacteria that can not live without light. In field experiments, the researchers used shields to block light from infected corals. Black band disease disappeared from the regions that were not exposed to light.
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