Shit – we’re killing the coral

Elkhorn Coral (Acropora palmata) is in a shitload of trouble.

Healthy Elkhorn Coral

Elkhorn coral was formerly the dominant species in shallow water (3 ft-16 ft (1-5 m) deep) throughout the Caribbean and on the Florida Reef Tract, forming extensive, densely aggregated thickets (stands) in areas of heavy surf. Coral colonies prefer exposed reef crest and fore reef environments in depths of less than 20 feet (6 m), although isolated corals may occur to 65 feet (20 m)….

Once found in continuous stands that extended along the front side of most coral reefs, the characteristic “Acropora palmata zone” supported a diverse assemblage of other invertebrates and fish. These zones have been largely transformed into rubble fields with few, isolated living colonies.

In the past decade, the population of Elkhorn coral has decreased by 90-95% primarily due to infections by the highly contagious “white pox“.

Coral colonies affected by white pox disease are characterized

Elkhorn Coral infected with white pox

by the presence of irregularly shaped white lesions where tissue has disappeared from the skeleton. Lesions range in area from a few square centimeters to greater than 80 cm2 and can develop simultaneously on all surfaces of the coral colony. The distinct white patches and the potential for tissue loss everywhere on the coral colony distinguish this disease from white-band disease, which develops at the base of a coral branch and progresses upward toward the branch tip in a concentric ring. Disease signs also clearly differ from coral bleaching and predation scars produced by the corallivorous snail, Coralliophila abbreviata.

The source of this infection has been a mystery until now. The answer is human excrement.  This is the first example of a disease transmitted from humans to invertebrates.

Nine years ago, a research team led by coral reef ecologists Kathryn Sutherland, now of Rollins College in Winter Park, Florida, and James Porter of the University of Georgia, Athens, linked white pox to a bacterium called Serratia marcescens, which is found in the intestines of humans and a handful of other animals. In humans, Serratia can cause respiratory and urinary tract infections. But although Sutherland and her team strongly suspected human waste—stemming from septic tanks that leak sewage into the Florida Keys’s porous bedrock—was the culprit, they had no proof that the disease didn’t start with Key deer, cats, seagulls, or any of the Caribbean’s other Serratia-harboring wildlife. “There was considerable skepticism—it was too easy to blame other things,” Porter says.

The duo and colleagues spent years collecting Serratia samples from healthy and diseased corals, from humans via a wastewater treatment facility in Key West, and from other animals. To obtain each sample’s genetic fingerprint, they added an enzyme that breaks up the bacterium’s genome wherever a specific gene sequence is found.

Because every strain’s genome differs slightly, each one yields a unique pattern of breaks. Comparing the patterns among all their samples, the team found only two that matched each other exactly: the Serratia strain found in white pox-afflicted coral and the one drawn from human waste.

This detective work was published in the online journal PLoS One

Human culpability in the demise of a threatened species necessitates an immediate response and supports ongoing mitigation to improve wastewater treatment in the Florida Keys, and elsewhere, in order to protect the health and biodiversity of coral reef ecosystems. Advanced wastewater treatment successfully removes Serratia marcescens to undetectable levels. However, most wastewater in the Keys and wider Caribbean is not treated, but rather is disposed of through in-ground receptacles within porous limestone substrate that permits leakage from these systems into near-shore waters. Human fecal contamination of near-shore and off-shore coral reef environments has been clearly demonstrated in the Florida Keys and elsewhere in the Caribbean and is associated with waterborne disease in humans.

Florida has committed nearly a billion dollars to improve waste water treatment. According to the article, Key West has not had a new case since implementing a new treatment centre in 2001. Will the rest of the Caribbean be able to get their shit together and protect the coral.

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2 Responses to Shit – we’re killing the coral

  1. Bill Baugh says:

    Thanks for the post. We need more posts about environmental issues and green products.


  2. I’m a long time watcher and I just imagined I’d stop by and say hello there for your first time. I seriously delight in your posts. Many thanks

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