Disease causes growths that obstruct turtle's vision
Green sea turtles, which are currently endangered, are facing another threat – a debilitating disease that is suspected to be due to human-induced pollution.
In the past three years, Karina Jones from James Cook University in Townsville, Australia has investigated fibropapillomatosis (FP) among green sea turtles in the Great Barrier Reef. FP is a turtle-specific herpes virus that remains dormant in almost 90 percent of all afflicted turtles.
Although the tumours are benign, they cause abnormal growths (as large as 30 centimetres across) on the turtles' eyes, mouth, flippers, tail, skin and internal organs; this can obstruct their vision, preventing them from finding food or detecting predators or boats.
Jones has identified an area near Cockle Bay at Magnetic Island (a popular tourist destination) as one of the hotspots of the disease. Here, roughly half of the turtles have been afflicted with the disease, compared to around 10 percent in the other areas of Cockle Bay.
The precise cause of the outbreak is yet to be determined, but environmental pollutants are high on the list of suspects. "We see these tumours in turtles in very localised hotspots around the world where there is heavy human activity." In healthy marine environments, many turtles do carry the virus, but it often remains dormant without any symptoms. This has led Jones to speculate that "there must be some external trigger that causes the tumour development."
The FP outbreak is not limited to the Great Barrier Reef, as there is also an increase of cases reported in Florida and Hawaii, particularly near onshore farming areas (see also article in NewScientist). Doug Mader, from the Turtle Hospital in Marathon, Florida, also suspects that pollution is to blame. His facility has seen an increase in the number of afflicted turtles over the last 20 years.
For Jones, the next step is to find out which contaminants are responsible for the outbreak. To this end, she and her team are looking into the historical water quality data, and comparing it with the present-day data. They will also carry out extensive tests on water samples to identify the heavy metals, fertilisers and pesticides present in the water.
As well-intentioned as their efforts may be, time continues to run out for the green sea turtle, though. The green sea turtle is listed as "Endangered" on the IUCN Red List of Threatened Species, with about 200,000 left worldwide.
As the second largest sea turtle in the world, the green sea turtle can grow up to 1.5 metres long and weigh up to 200 kilogram’s. They live primarily in warm, tropical seas. They lay their eggs on beaches and bays in Australia, Florida, Hawaii, Costa Rica and Japan. Besides the current FP outbreak, they also face several threats, including the excessive harvesting of their eggs, hunting, ending up as by-catch in fishing nets, and the loss of their nesting grounds as beaches get developed for tourism.