(New Scientist)

It’s a turtle tragedy. Tumors are crippling an increasing number of green sea turtles on Australia’s Great Barrier Reef, with pollution being investigated as the prime culprit.

The animals have a turtle-specific herpesvirus that causes fibropapillomatosis, a condition in which disfiguring tumors grow on the eyes, flippers, tail, shell or internal organs.

“The tumors are benign but can grow up to [about a foot] in size and block the turtles’ vision,” says Karina Jones of James Cook University. “This means they can’t find food or see predators or boats.”

Turtles with tumors are also more vulnerable to other infections, she says. “Severely affected turtles are quite skinny and have other pathogens affecting them. That’s why they die.”

The unpublished results of surveys by Jones’s team this year show that herpesvirus is most prevalent within a narrow stretch of Cockle Bay at Magnetic Island, a popular tourist destination in the middle of the reef. Roughly half the turtles in this hot spot have fibropapillomatosis, compared with less than 10 percent of turtles sampled across the rest of Cockle Bay.

Tumors are crippling an increasing number of green sea turtles on Australia’s Great Barrier Reef. Pollution is being investigated as the prime culprit. (Karina Jones)

The cause remains unclear, but environmental contaminants are at the top of the suspect list. “We see these tumors in turtles in very localized hot spots around the world where there is heavy human activity,” Jones says.

Turtles in healthy marine environments may carry the virus, but it often lies dormant with no symptoms, she says. “We think there must be some external trigger that causes the tumor development,” she says.

Fibropapillomatosis has also become increasingly common in turtles in Florida and Hawaii, particularly near onshore farming areas, which may be the source of pollution. Over the past 20 years, Doug Mader of the Turtle Hospital in Marathon, Fla., says he has gone from treating six to eight turtles per month to the same number per week.

Mader agrees that human pollution is probably to blame. “It is thought that pollution may weaken their immune systems, thus rendering them more susceptible to disease,” he says.

The next step is to try to pin down the contaminants that may be responsible, Jones says. Her team is looking for clues in historical water quality data and is also planning to test water samples for a range of chemicals, including heavy metals and fertilizer and pesticide components.

“The field is very challenging because there are so many questions to ask,” she says. “But it’s always good to ask the big questions.”

The disease, which is spreading, is specific to sea turtles. (Karina Jones)

New Scientist