Grisly tumors that have been afflicting young green sea turtles off Florida shores are likely worsened by onshore pollution that weaken the teen turtle’s immune systems.
In a study published this week in the Journal of Wildlife Diseases, a team of Florida Atlantic University researchers examined turtles in the Indian River Lagoon over the last two decades, where about half have been infected with the herpes virus, Green Turtle Fibropapillomatosis, and sprout tumors. When they compared them to tumor-free turtles in more pristine waters off Cape Canaveral, they found the lagoon turtles had far weaker immune systems.
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While other studies have tied diseases to pollution, the study is the first to link pollution to a weakened immune system in diseased turtles — which grew more weak once infected.
“That sort of suggests it's a vicious cycle,” said Dr. Sarah Milton, chair of FAU's department of biological sciences. “If you're in the lagoon, you're immunosuppressed and then you get the disease, and that probably makes you even more immunosuppressed.”
The virus that causes the tumors has been around as long as turtles, or about 3 million years, and can be found in turtles around the planet. But it’s only been over the last century that infected juvenile turtles began developing the tumors, which can grow to the size of a cantaloupe.
The tumors almost always appear on young turtlesthat return to inshore waters for their teen years before heading out to the open ocean once they mature. And those turtles are usually found in pollution hotspots in Hawaii, the Florida Keys and the Indian River Lagoon, Milton said.
“They're polluted. They get warmer. Seagrass beds die because of the pollution. There's all these stressors that are going on in nearshore areas,” she said. “So our hypothesis was that in these nearshore areas, the animals were stressed enough that it was depressing the immune system.”
While the tumors themselves are not fatal, they can interfere with the turtles' ability to swim, see and eat or become a path for infections if the turtles cut themselves.
“You get them all over their bodies, particularly the soft tissues like the armpits and the groin area. Also on their eyes,” Milton said.
The tumors can be removed with lasers, but they often regrow. Only about half the treated turtles survive, she said.
To confirm the pollution connection, the research team examined juvenile turtles in the Trident Basin off Cape Canaveral.
“It's literally where the Trident submarines turn around. So it's a very protected area and therefore not polluted,” Milton said.
When they compared the two branches of the immune system — the innate branch that deals with common ailments and the adaptive branch that fights specific pathogens — they found the Indian River Lagoon turtles considerably weaker in both.
“Just being in the environment was enough to make them immunosuppressed,” she said. “And the ones that had the disease were even worse off than the ones that did not show the disease.”
The findings add to a surge in evidence tying pollution to specific damage in the ocean's plants and animals being worsened by climate change. Heavier rainfalls and rising sea levels mean even more pollution is pouring off the coast.
That's worsened seagrass die-offs and coral disease. Microplastics have been found all over the ocean, from the North Atlantic to the Galapagos Islands. Antidepressants and other pharmaceuticals have turned up in bonefish with altered behavior.
Pollution in the Indian River Lagoon has also been linked to a fungus on dolphin and flesh-eating bacteria in fish, Milton said.
“When they come into the lagoon, they don't have any [tumors]. And then once they've been there for a little while, the [tumors] start showing up,” she said. “Basically, these are indicator species that are telling us that this is a very polluted area.”
