Dilemma of the Caribbean

Its porous soil carries sewage to ocean, causes pox in corals

By Tiasa Adhya
Published: Saturday 15 October 2011

ELKHORN coral looks just like elk antlers. With its complex, large branches, this important reef-building coral in the Caribbean is haven to numerous reef species. But, not any more. The Caribbean has lost 90 per cent of the coral in 15 years. Apart from human activity and warming of seas, a disease called white pox is blamed for making elkhorn coral an endangered species.

As it appears, tissues of the coral come off, leaving the skeleton exposed and killing it. Scientists from Rollins College and University of Georgia in the US recently implicated sewage for the pox. Though scientists had long suspected PDR60 strain of faecal bacteria Serratio marcescens as the culprit, they could not prove it. After all, the bacteria is found in the guts of several animals.

The team genetically analysed the pathogen isolated from the faecal matter of human and other animals. Only the strain in humans matched with the strain causing white pox. To ascertain the finding, they swabbed small fragments of healthy coral with various bacterial strains from the faecal matter of several animals, including humans. The strain from human faeces made it sick in five days, the scientists noted in PLoS ONE on August 17.

The movement of pathogens from wildlife to humans is well documented. For instance, bird flu and HIV/AIDS. But this is the first documented incidence of a human pathogen jumping into an animal, that too a marine invertebrate, says James Porter, co-author of the study. S marcescens is known to cause meningitis and pneumonia. The scientists blame the disease on the way Florida Keys (a coral archipelago) treats its sewage. The islands on porous limestone bedrock use traditional septic tanks. Leaks from them travel through the bedrock into the ocean, sickening corals, they add.

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