The Worrying Case of the Turtle Tumors

Green Turtle dreamstime 15787016 The Worrying Case of the Turtle TumorsResearchers may have solved the mystery behind a disease that leaves Hawaiin sea turtles with hideous tumors – and the tracks lead back to land, and to an amino acid called arginine.

The Green sea turtle (Chelonia mydas) is an endangered species found around the world, mostly in tropical seas. Off Hawaii, populations have been relatively healthy, and even growing. But in the 1980s, researchers noticed an uptick in a disease called fibropapillomatosis (FP), which can cause massive tumors to grow on a turtle’s skin and face. Animal health specialists eventually linked the disease to a herpes virus, perhaps spread by parasites. Why some turtles were struck by FP while others remained healthy, however, remained a puzzle.

In an effort to get a better handle on the threat, three researchers with National Oceanic and Atmospheric Administration’s Pacific Islands Fisheries Center decided to take a close look at the medical charts of nearly 4,000 turtles that washed up dead or moribund on Hawaii’s beaches between 1982 and 2009. Then, they looked for clues that might explain the distribution of the turtles with FP, examining links to everything from age to where the turtles lived and what they ate.

Although they were working with imperfect data, the researchers saw some intriguing patterns emerge from the numbers, they report in PLOS One. The disease appears to strike subadult turtles the hardest, for example, perhaps because adults develop immunity. More interesting, however, was that sick turtles were often found near landscapes with big “nitrogen footprints.” The nutrient, which is heavily used as a farm fertilizer and produced by sewage treatment plants, often washes into nearshore waters, where it can fuel algal growth. Indeed, after 1950, invasive algae had begun to thrive in Hawaiian waters with high nutrient loads – and many green turtles had become dependent on the exotic plants for up to 90% of their food.

“The implications of this dietary shift may be profound,” write Kyle S. Van Houtan and his colleagues. That’s because the invasive algae store up, or “sequester,” nitrogen in their tissues, specifically in the amino acid arginine. And arginine, it turns out, “is specifically important for herpesviruses which are linked to FP tumors.” In particular, previous studies have found that the amino acid promotes eye-related tumors. “This is particularly relevant,” the authors note, “as 93% of Hawaiian green turtles with FP have ocular tumors.”

Although the links between nitrogen pollution, turtle diet and disease seem strong, the authors “urge interpretative caution,” since “many factors contribute to the course of an infectious disease.” Still, the sleuthing suggests that “environmental factors are significant in promoting FP” and that the role of nitrogen pollution – and arginine – in viral diseases is worth a closer look. David Malakoff | October 12, 2010

Source: Van Houtan, K., Hargrove, S., & Balazs, G. (2010). Land Use, Macroalgae, and a Tumor-Forming Disease in Marine Turtles. PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012900

Image © Richard Carey | Dreamstime.com

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4 Comments

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  • Jay October 12, 2010 at 7:57 pm

    This is not “news.” Locals, who are excellent observers of their environment, having been discussing this cause for the sea turtle’s tumors. This is another case of ill-informed scholary types from the mainland claim discovery but do not give credit to the indigenous people.

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    • Kainoa October 15, 2010 at 8:46 pm

      Jay, I agree that most of the local Hawaiians who have been around since the 1970s and have seen dramatic transformations to their coasts have considered some of the links this study puts forth. The disease is here more than there, and that algae and pollution play some role. But that is wholly different from understanding the disease on a biochemical level, that it’s herpes, and all the stuff about Nitrogen and amino acids. Having scientists like these NOAA ecologists working with locals is what we need to protect Hawaii Nei and the honu. George “Keoki” Balazs in particular has been studying why these turtles are dying since 1976. He and his team are hardly “ill-informed” and I would be a stretch to call him a mainlander. They’re working hard and you should appreciate that.

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  • fkf October 13, 2010 at 12:39 pm

    Jay- Your comment’s accusing tone detracts from the message you intend to make. It is absolutely correct that native Hawaiians are adept observers and scientists of their environment and they and other locals have surmised as to the cause of the FP tumors. However to have it backed up with a bona fide research project by experts is vetry valuable to getting something done. And to call the scientists esp George Balazs with 30+ years experience in Hawaii studying green sea turtles “ill-informed scholary types from the mainland” is just plain wrong.

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