Infection occurs after a bacterial mat forms a black band, which migrates across healthy coral colonies. The mat is comprised of multiple species of bacteria, mainly cyanobacteria (blue-green algae) and bacteria associated with the sulfur-cycle. "We don't really know where they come from or how they make such a complicated bacterial community, but once formed it can kill coral quickly," eating through 4 millimeters a day, Sato said. The study area had been disease-free during the past 15 years; therefore the sudden appearance of multiple infections since 2006 is being considered an epizootic. The researchers also examined whether new infections were influenced by water temperature and light intensity. They found high temperatures stressed the coral hosts and increased susceptibility to infections. But they believe light might be the more important facilitator of disease, with most infections occurring two months before water temperature peaked when light levels were greatest. The researchers believe the bacteria responsible for the disease are transported by water movement. Fish may also be responsible, eating and then spitting out bacteria as they move from colony to colony. Humans could also be contributing to the spread of the disease. "Black band disease is possibly impacted by sewage in the sea. The more nutrients around the disease mat, the faster it grows," said Sato. "Past studies show that diseased areas are common around where people live but it's not always the case on the Great Barrier Reef as it has been found in remote areas too." Related Links: |
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