Human faeces is killing corals

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In addition to global warming and ocean acidification, corals can now add faecal matter to their litany of woes from humans, according to research published in a recent issue of the online journal PLoS ONE.

In this study, Kathryn Sutherland and coauthors have isolated the key source of the bacterial pathogen that has devastated the Elkhorn coral (Acropora palmata) in the Caribbean—human sewage.

The Elkhorn coral was once the most common species in the Caribbean, but its global population has been severely decimated to a tenth of what they were 15 years ago.

One of the major causes of this decline is the dreaded white pox disease, which kills off living coral tissue to leave behind white patches of dead coral skeleton.

It has been known since 2002 that the bacterium responsible for white pox disease (Serratia marcescens) was the same species as that found in humans, where it has been known to cause respiratory, wound and urinary tract infections, meningitis, and pneumonia. However, the bacterium is also found in a wide variety of animals, such as deer and seagulls, so it remained for the authors to find the smoking gun.

The authors carried out a series of experiments in closed marine aquariums, in which small fragments of Elkhorn coral were collected from 19 apparently healthy colonies at Western Sambo Reef in Florida (with one to four fragments being collected from each colony).

Three fragments were placed in each aquarium (making sure that each of these fragments came from a different colony), and the coral fragments in each aquarium were inoculated with Serratia obtained from a variety of reef sources, as well as from untreated waste water from the Key West waste water treatment facility.

The authors found that coral fragments exposed to bacteria from waste water developed white pox disease in as little as four days, conclusively demonstrating that the bacterial strain from humans is the culprit.

This is the first instance of a reverse zoonosis (the transmission of an infectious disease from humans to non-humans) in a marine invertebrate, and the authors urge the improvement of waste water treatment in order to protect the health and biodiversity of coral reef ecosystems.

For more information, see the paper: Sutherland, KP, S Shaban, JL Joyner, JW Porter and EK Lipp (2011) Human pathogen shown to cause disease in the threatened eklhorn coral Acropora palmata. PLoS ONE 6, e23468, doi: 10.1371/journal.pone.0023468.

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