for National Geographic News
In many parts of the world where sewage treatment is lacking, raw human waste spills into the open sea. Now, research suggests that certain microbes in the human gut are responsible for two coral diseases that have devastated large patches of reef.
Billions of bacteria live in the intestines of each person. Many of these microbes, including Serratia marcescens, don't typically cause illness in people. Others, such as Arcobacter, can cause diarrhea in children when too abundant.
But these two intestinal bugs and many others are much less benign when they meet coral, according to scientists who have linked the bacteria with white pox and black band disease, which have decimated two types of coral in recent years.
White pox has nearly wiped out hornlike elkhorn coral in some reefs in the Caribbean and elsewhere. Black band disease has stricken round coral in many reefs throughout the seas.
"The one-two punch from those two diseases alone could explain the vast majority of disease impact on reefs," said Bruce Fouke of the University of Illinois at Urbana-Champaign.
A Killer Consortium
Fouke and his colleagues have been researching black band disease in Curacao, a Caribbean island in the Netherlands Antilles.
Black band disease consists of a dense mat of microbes. The disease begins as a small concentric ring that expands in circumference "like a rubber band" as it moves around the coral, and then contracts as it eats its way across the opposite side, Fouke said. "It leaves nothing but bare skeleton behind it," he said.
Fouke initially thought that three or four types of bacteria might be involved in black band disease. Instead, he found a legion of microbes. "Our research shows there are over 40 organisms that live" in the disease mat, Fouke said.
In the May issue of Applied and Environmental Microbiology, Fouke's team reported the results of extensive laboratory and genetic work on the numerous bacteria involved in black band disease.
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