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Hawai’i's sea turtles are afflicted with chronic and often lethal tumors caused by consuming non-native algae, “superweeds,” along coastlines where nutrient pollution is unchecked. The disease that causes these tumors is considered the leading cause of death in endangered green sea turtles. The new research was just published in the scientific journal PeerJ.
Turtles that graze on blooms of invasive seaweeds end up with a diet that is rich in a particular amino acid, arginine, which promotes the virus that creates the tumors. Scientists at the University of Hawai’i at Mānoa and their NOAA colleague estimate that adult turtles foraging at high-nutrient grazing sites increase their arginine intake 17—26 g daily, up to 14 times the background level.
“For years, local ocean lovers have known that our green turtles have had awful tumors on their heads, eyes and front flippers,” said UH Mānoa Marine Biology Professor Celia Smith, who worked with Kyle S. Van Houton of NOAA’s Turtle Research Program on this study. “Many hypotheses were offered to explain the tumors, but we kept coming back to the observation that urban reefs – those near dense populations – are the sites with greater numbers of sick turtles. We had no mechanism for this disease.”
More than 60 percent of turtles in
Kāne’ohe Bay have been observed to bear tumors. Kihei, Maui, has been called a “ground zero” for fibropapillomatosis, the disease that is caused by a herpes virus and manifests as tumors in turtles. Humans appear unaffected by the disease.
Van Houtan and colleagues previously described an epidemiological link between tumors and coastal eutrophication, that is, the enrichment of coastal waters with nutrients from land-based sources of pollution such as wastewater or agricultural fertilizers. This new study analyzed the actual tissues from tumored green turtles and the amounts of arginine in the dominant algae forage species from across Hawai’i.
The analysis revealed remarkably high levels of arginine in tissues of invasive seaweeds harvested under nutrient-rich conditions, such as those affected by nitrogen from land-based pollution. These are the same conditions that promote algal blooms. The non-native algae “superweeds” grow so quickly when fertilized that some can double their weight in a period of two days.
Image shows juvenile green turtle with tumors (credit: Chris Stankis, Flickr/Bluewavechris).
Read more at University of Hawai’i.
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