Sea turtles in Hawai’i have been found to be afflicted with chronic, and often times lethal tumors that are caused by consuming non-native algae along the island state’s coastlines where nutrient pollution is unchecked. The disease that causes these tumors is now considered the leading cause of death for the endangered green sea turtle.
By grazing on blooms of invasive seaweeds, turtles end up with a diet that’s jam packed with particular amino acid, known as arginine, which promotes the virus which creates the tumors. Scientists at the University of Hawai’i at Mānoa and the National Oceanic and Atmospheric Administration (NOAA) have estimated that turtles grazing at these high-nutrient sites are increasing their arginine intake by 17 to 26 grams daily, nearly 14 times the previous 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% of the turtles in the Kāne’ohe Bay have been found to bear tumors as a result of this disease. Kihei has been called a “ground zero” for fibropapillomatosis, the disease that is caused by a herpes virus and manifests as tumors in turtles, but appears to not affect humans.
Van Houtan and his colleagues have previously described an epidemiological link between tumors and coastal eutrophication, which is the enrichment of coastal waters with nutrients from land-based sources of pollution such as wastewater or agricultural fertilizers. However, this new study actually analyzed the tissues from the afflicted turtles and the amounts of arginine in the dominant algae forage species from across Hawai’i.
What the analysis found was that there are incredibly 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.
Read more about the story at Smithsonian.