College of LAS « Illinois

Geology and Microbiology

Heavy Metals, Human Sewage May Contribute to Killing Coral Reefs

Photo of diseased coral reef

Global warming may not be the only culprit killing the coral reefs. Human sewage and metals from shipyard discharge may be involved in the development and spread of deadly black band disease in corals, say researchers in LAS.

"Black band disease is characterized by a ring-shaped bacterial mat that migrates across a coral colony, leaving dead tissue in its wake," says geologist Bruce Fouke. "Like a rainforest, a coral reef system is a cradle of biodiversity. If we destroy the reefs, we destroy a major portion of the ocean's ability to reproduce."

To better understand the disease, Fouke and his colleagues—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. They mapped outbreaks of the disease along the reef and then looked for metals such as aluminum, cadmium, and zinc that are common pollutants from shipyards and oil refineries.

They discovered that the highest number of infected corals, as well as the highest concentration of dissolved metals, occurred near the city of St. Annabaai, which has a major harbor and a large oil refinery. 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 mucus-rich biofilm that provides protection from light, exposure, and sedimentation, Fouke says. "Environmental stresses cause corals to secrete more of this mucus to coat their outer tissues. This leads to elevated levels of natural microbial populations as well as the introduction of new, potentially harmful bacterial populations." Among the organisms the researchers found inhabiting the black band biomat were Arcobacter and Campylobacter, which are human pathogens and could be a direct link to raw sewage.

Summer 2002