Human Wastewater Pinned to Coral Disease

Sewage is to blame for a disease that is killing an endangered coral.

Photo by NOAA's Florida Keys National Marine Sanctuary/Wikimedia Commons There's little doubt that humans negatively affect marine ecosystems - sometimes consciously, other times accidentally. But providing solid evidence for cause and effect has been an exhaustive endeavor for some researchers looking to better protect the environment.

But sometimes you learn about cases in which the evidence is strong enough to get the ball rolling on tackling a problem or shaping policy.

This week, one example is scientists linking a human pathogen to white pox, a disease responsible for killing large portions of elkhorn coral (Acropora palmata) off the coast of the Florida Keys. The IUCN placed this species of coral as critically endangered, listing white pox as its primary threat.

Though scientists long suspected a bacterium infected the coral via human sewage, they now have more definitive evidence that this is the case. By using a set of principles known as Koch's postulates to guide the experiment, the team introduced isolates of the bacterium Serratia marcescens to in 11 aquaria with healthy elkhorn coral. They conducted genetic tests on the bacterial strains before and after infection to ensure the same pathogen was responsible for the disease in each tank. E. coli, sediment and seawater were used as controls.

When given bacteria isolated from human wastewater, the coral developed white pox within four days, providing the clearest evidence to-date that human activities are linked to this virulent strain of the disease. The team also suggests that a snail species and maybe even surrounding coral can serve as vectors of the bacterium.

In humans, the bacterium is known to cause respiratory problems, whereas in coral, it degrades the soft tissue of coral, often leaving the organisms' white skeletons in its wake.

With the technological advances used in modern wastewater treatment facilities, how does Serratia marcescens make it to seawater to being with?

Other research shows that these areas lack the type of facilities found in most U.S. counties. Instead, they use porous limestone systems to clean water, where it can leak into local bodies of water. A master plan from 2000 seeks to replace these systems, but it's not clear whether the problem has been addressed.

James Porter, a professor of ecology at the University of Georgia and coauthor of the study, told Discovery News that boat pump-out vessels that store human waste from other boats could have been a part of the problem, but new rules requiring them to be handled dockside are being implemented.

Despite Key West leading the efforts in updating its facilities to comply with Advanced Wastewater Treatment (AWT) standards, Porter said other areas in the Florida keys aren't financially and politically onboard to build new systems and make them AWT-compliant.

Now with stronger evidence linking human waste to white pox, he said the findings should help develop the political will to revamp these wastewater systems in the Keys.