Abstract
The tumor-forming disease fibropapillomatosis (FP) has afflicted sea turtle populations for decades with no clear cause. A lineage of α-herpesviruses associated with these tumors has existed for millennia, suggesting environmental factors are responsible for its recent epidemiology. In previous work, we described how herpesviruses could cause FP tumors through a metabolic influx of arginine. We demonstrated the disease prevails in chronically eutrophied coastal waters, and that turtles foraging in these sites might consume arginine-enriched macroalgae. Here, we test the idea using High-Performance Liquid Chromatography (HPLC) to describe the amino acid profiles of green turtle (Chelonia mydas) tumors and five common forage species of macroalgae from a range of eutrophic states. Tumors were notably elevated in glycine, proline, alanine, arginine, and serine and depleted in lysine when compared to baseline samples. All macroalgae from eutrophic locations had elevated arginine, and all species preferentially stored environmental nitrogen as arginine even at oligotrophic sites. From these results, we estimate adult turtles foraging at eutrophied sites increase their arginine intake 17–26 g daily, up to 14 times the background level. Arginine nitrogen increased with total macroalgae nitrogen and watershed nitrogen, and the invasive rhodophyte Hypnea musciformis significantly outperformed all other species in this respect. Our results confirm that eutrophication substantially increases the arginine content of macroalgae, which may metabolically promote latent herpesviruses and cause FP tumors in green turtles.
Highlights
Fibropapillomatosis (FP) is a chronic and often lethal tumor-forming disease in sea turtles (Fig. 1A)
In this study we demonstrated how eutrophication increases the arginine in invasive marine macroalgae; that this significantly boosts the arginine intake by foraging green turtles, and that arginine is elevated in tumors from diseased green turtles
We calculated adult turtles foraging in eutrophic habitats on invasive algae might boost their arginine intake 5–14 times, consuming a total of 22–28 g of arginine daily
Summary
Fibropapillomatosis (FP) is a chronic and often lethal tumor-forming disease in sea turtles (Fig. 1A). It became a panzootic in green turtles in the 1980s, prompting concern that it was a serious threat to their global conservation (Chaloupka et al, 2008; Herbst, 1994). Though most green turtle population indices have increased steadily since (Seminoff et al, 2014), the disease remains prevalent and in several locations its incidence is still increasing (Van Houtan, Hargrove & Balazs, 2010). How to cite this article Van Houtan et al (2014), Eutrophication and the dietary promotion of sea turtle tumors. The ecological promotion of the disease is made further interesting as FP tumors have a proposed viral origin
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