Examining the turtles' tumors revealed unusually high amounts of a molecule called arginine - a trait the sick reptiles shared with their primary food source, algae. One species of algae, Hypnea musciformis, is packed with arginine; this invasive species both outcompetes local algae and is less nutritious, so sea turtles need to eat twice as much Hypnea to get the same calories native algae would offer.
Turtles who chow down on Hypnea, the scientist believe, suffer from the highest instance of tumors. "If this disease is a car, arginine its fuel," Van Houtan says. These reptiles may be ingesting anywhere from 5 to 14 times more arginine near polluted reefs, the scientists report in the journal PeerJ.
When sewage leaches into the sea - specifically, the nitrogen within the pollution - it kindles algal growth, triggering a "nutrient cascade" that ends up as turtle tumors. That's bad news for the turtles, who are also threatened by habitat loss and fishing hooks (Hawaii's green turtles are listed as threatened under the Endangered Species Act).
If it goes untreated, fibropapillomatosis is deadly. But there's a ray of hope for turtles who receive medical attention, as one Florida sea turtle named Yertle demonstrated back in May. And despite the emergence of this disease, which is becoming more common in some Hawaiian areas, the green turtle population is slowly recovering after years of overharvesting.