Pollution from urban areas and farms in Hawaii may be contributing to a tumor-forming disease in endangered sea turtles, a new study has found. According to the researchers, nitrogen in runoff gets stored in the turtles’ food and consequently gives sleepy herpesviruses the fuel they need to cause the often fatal tumors that have afflicted sea turtle populations for decades. The work has been published in PeerJ.
Fibropapillomatosis (FP) is an often fatal tumor-forming disease that affects sea turtles across the globe. Previous work identified DNA from a group of viruses called alpha-herpesviruses in these tumors, but not in adjacent healthy tissues. This suggested a viral origin of this disease, but later studies found that these viruses were actually present in every sea turtle tested, even healthy turtles. This indicated that these viruses may be dormant, or subclinical, in sea turtles, but that something is acting as a trigger for them to promote tumor growth.
It has recently emerged that the amino acid arginine might play a significant role in the life cycle of herpesviruses. Laboratory studies have shown that arginine is required for herpesviruses to infect cells and also makes up part of a virus’ protective coat. Furthermore, there is some evidence that suggests that arginine can promote viral tumors.
Since it is known that plants can store excess nitrogen in arginine, researchers wondered whether the same might be true for algae. As sea turtles dine on algae, and nitrogen-rich runoff can spur algal blooms, scientists considered if that pollution could be triggering a cascade of events that unfortunately result in tumor formation in sea turtles. Indeed, back in 2010, this team published a study that found that FP is more prevalent in areas with high levels of nitrogen runoff, but the link with arginine had never been studied before.
To address this missing link, researchers from Duke University, the University of Hawaii and the National Oceanic Atmospheric Administration looked at the levels of arginine in algae and green turtles across Hawaii. They found that tumors were elevated in several different amino acids, including alanine. Furthermore, they discovered that algae from polluted areas contained unusually high levels of arginine, and that all species stored environmental nitrogen as arginine.
They also found that an invasive red algae species had alarmingly high levels of arginine when compared with native species. This species is unfortunately more successful than native species and consequently makes up as much as 90% of the turtles’ diet. It also provides fewer calories to the turtles, so they end up eating more of it.
“The energy and arginine content [of the algae] may therefore act as a sort of one-two punch for promoting this disease,” noted the researchers.
This study highlights the potential problems that marine organisms face as a result of human-induced pollution. Further research could be helpful in the planning of environmental management studies. “If research continues to support this hypothesis, we probably need to reconsider our current ways of managing coastal nutrients,” lead author Kyle Van Houtan said in a news-release.
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