A new study by researchers at Florida Atlantic University literally sheds “light” on a way to improve the health of endangered green sea turtles (Chelonia mydas) prone to a disease called fibropapillomatosis. Affecting around 60 percent of sea turtles in certain subpopulations, juveniles are most susceptible to this disease which causes the growth of large, debilitating tumors on the skin, eyes and shell.
Turtles with fibropapillomatosis are treated at rehabilitation centers where the tumors are surgically removed. Unfortunately, many of them do not survive or the tumors grow back.
One solution to help this population of sea turtles could be as simple as sunlight. Many turtle rehabilitation facilities have enclosures that limit sea turtle exposure to natural ultraviolet (UV) light. Sunlight is an important source of vitamin D, an essential nutrient in vertebrates that plays many physiological roles. It is important to note that sea turtles with fibropapillomatosis show reduced levels of vitamin D and variations in blood chemical parameters.
For the study, FAU researchers compared vitamin D levels in green sea turtles with and without obvious fibropapillomatosis to determine if sun exposure would influence vitamin D levels and other health parameters. They also looked at the differences between turtles brought to rehabilitation centers and healthy juvenile green turtles captured from the wild.
Additionally, researchers investigated whether higher levels of sun exposure increased vitamin D levels in sea turtles undergoing treatment for fibropapillomatosis compared to turtles receiving less ultraviolet light. As turtles with and without visible tumors entered the rehabilitation center, the researchers also checked whether there was a correlation between sun exposure, vitamin D and tumor regrowth.
Turtles receiving the treatment were housed in tanks exposed to varying levels of sunlight for up to six months. The researchers looked at hematology and blood chemistry parameters as well as vitamin D, parathyroid hormone (regulates blood calcium levels) and ionized calcium levels. Turtles that underwent tumor removal surgery were monitored for any regrowth.
The results of the study, published in the journal Animals, found that turtles exposed to greater sunlight had greater increases in plasma vitamin D and more successful recovery. Vitamin D levels increased over time in the rehabilitating turtles, with the greatest increases seen when the turtles were exposed to higher levels of UV light and for longer durations. Those turtles kept in the sunbeds experienced less tumor regrowth than those exposed to low UV light conditions. The results suggest that increasing sun exposure in rehabilitation facilities can improve the health and recovery of green sea turtles with fibropapillomatosis.
Upon ingestion, tumor turtles had lower plasma vitamin D and ionized calcium levels and higher parathyroid hormone levels compared to wild-caught and rehabilitation turtles without obvious tumors.
“The data from our study suggests that a potential method to improve the fate of sea turtles with this disease is to increase their exposure to UV light during rehabilitation,” said Sarah L. Milton, Ph.D., Senior Author, Chair and Professor, Department of Biological Sciences, FAU Charles E. Schmidt College of Science, and Fellow of the FAU Stiles-Nicholson Brain Institute and the FAU Institute for Human Health and Disease Intervention (I-Health). “Although a cure for this disease has not yet been discovered, we have shown that exposure to higher UV light increases vitamin D in turtles, as in other animals, including humans. Increased plasma levels of vitamin D are then correlated with lower rates of disease, so this potential for improved health could contribute to better recovery.For future studies, we would be interested to see if there are any links. direct links between vitamin D levels and immune function.
The study’s co-author is Victoria E. Garefino, an FAU graduate of Milton’s lab. This research was funded by the Friends of Gumbo Limbo and National Save the Sea Turtle Foundation Fellowships awarded to Milton.