For decades, green sea turtles, once considered a delicacy of the sea and nearly hunted to extinction in Florida and around the world, have been plagued by a virus that causes cauliflower-like tumors to sprout from their eyes, mouths, fins and soft tissue.
Now researchers think they have an answer for what’s causing the tumors: pollution. And that discovery may have wider implications about the oceans’ health.
“These things are all lining up in a powerful way,” said Kyle Van Houtan, a National Oceanic and Atmospheric Administration scientist based in Hawaii. “We realize we have a lot of work, but we think we’re on the right track.”
But the study has caused a flap in the turtle world. This month, after the journal PeerJ published Van Houtan’s study, seven scientists including Thierry Work, another Honolulu-based government scientist, posted a comment titled, “The story of invasive algae, arginine, and turtle tumors does not make sense.”
The dispute pits relative newcomers to the turtle cause against the old guard. Van Houtan is a Duke University ecologist who last year won a prestigious early-career award that comes with five years of research funding. Lately his research has focused on the effects of climate change. Work is a veteran wildlife disease specialist and veterinarian with the U.S. Geological Society posted at the Honolulu field station for more than two decades.
“It makes for a sexy story, but it just doesn’t hold up,” Work said in an interview. “You need to look at all the answers and weigh them. You can’t just go with your pet theory and ignore all the other evidence that might not fit with your world view.”
In the 1980s, turtles started turning up on beaches from Florida to Hawaii with gruesome growths blooming on their pug-nosed faces. The tumors, caused by a herpesvirus called fibropapillomatosis (FP), were first documented in turtles in 1938 in the Florida Keys.
Scientists feared the virus might become pandemic, wiping out a species that had existed for 200 million years. Then, just as mysteriously, the virus seemed to subside. Protected by the Endangered Species Act in 1978, green turtles began to rebound in Florida. The number of nesting green turtles went from just a few dozen in the 1980s to more than 35,000 in 2013.
But the tumor mystery remained unsolved, troubling scientists who wonder if another outbreak might occur.
While the virus has popped up in all seven species of marine turtles, it hit greens the hardest and green turtles were already in danger from heavy harvesting. The local Keys’ population was nearly wiped out by the early 1900s. They were easy to catch — they grazed on seagrass pastures surrounding the islands — and easy to ship once hunters figured out the 350-pound adults survived if flipped on their backs. Their green flesh was also considered the tastiest of the turtles. Islamorada’s popular Green Turtle Inn still bears the neon turtle sign that beckoned tourists to try its turtle steaks, soups and chowders in the 1940s and 50s.
“We were worried that it could have been a runaway thing and it’s just a matter of time before all turtles get it,” said Allen Foley, a wildlife biologist with the Florida Fish and Wildlife Conservation Commission.
Tumor-deformed turtles appeared most frequently in the warm waters off South Florida and Hawaii and always in older juveniles, who return to coastal estuaries after spending their early years in deep water.
Richie Moretti, who founded Marathon’s Turtle Hospital in the 1980s, first noticed the growths in 1984 and consulted a vet who recommended tying them off with fishing line. Sure enough, the tumors dried out and fell off. But they almost always regrew.
The tumors seemed to be influenced by temperature: if a turtle was exposed to the virus in October, a tumor wouldn’t sprout until June or July, he said. If it was infected in May, a tumor would still appear in June or July.
Over the years treatment improved. Vets now use lasers to remove tumors, not fishing line. They also found if they removed all of the tumor tissue, tumors were unlikely to grow back.
The rate of the disease in Florida also declined, Foley said. After peaking between 1998 and 2000 with about 33 percent of turtles showing tumors, he said the number dropped to 15 percent in 2008. In recent years, the rates have hovered around 20 percent statewide, he said.
“It seems the population is handling it,” Foley said.
But Moretti said about 50 percent of the turtles coming to the hospital in Marathon still have tumors, suggesting the numbers are not falling in warmer waters near populated coasts.
“Every year it gets worse and worse,” he said. “After 30 years, I’d sure like to get some answers.”
Researchers may debate the trigger, but they have long suspected pollution plays a part.
“That’s really a no-brainer,” Foley said.
And with more attention paid to climate change, some believe rising sea temperatures aggravate the disease.
“It’s basic chemistry,” said Billy Causey, who has studied sea turtles since the 1960s and managed NOAA’s marine sanctuaries in the Keys since 1983. “You heat water a little bit and nothing happens. But then you add chemicals to the water, certainly things accelerate.”
Van Houtan, the NOAA scientist who concluded pollution was causing the tumors, originally was drawn to Hawaii by the rich trove of turtle data collected by scientists over three decades. In 2010 he published a study that found the disease had increased around the islands in as many places, if not more, than it had decreased, mostly in heavily polluted waters.
“It raised a lot of questions,” Van Houtan said. “We really needed to drill down and document it in a rigorous way.”
Work, the long-time U.S. Geological Society veterinarian, was intrigued when he heard about Van Houtan’s analysis.
“I thought it sounded plausible,” he said, suggesting that turtles congregated in polluted waters because the algae, a species imported from Florida in the 1950s by commercial growers, thrived in nutrient-rich waters. In the years since, the Florida algae has virtually wiped out native algae.
Work thought Van Houtan might have found sick turtles in polluted waters because there were more turtles and “more opportunities for the virus to be transmitted,” he said.
In September, Van Houtan published his second study that tied the tumors to nutrients found in pollution. When excess nutrients in pollution flood the seas, algae — one of the green turtle’s primary food sources — hoard it, storing the nutrients in an amino acid called arginine. By cross-referencing polluted bays and lagoons in Hawaii with high rates of tumors in turtles, and then examining the levels of arginine in both, Van Houtan and University of Hawaii marine botanist Celia Smith concluded arginine was the fuel powering the tumors.
Work said he found two major problems with the second study. To link the arginine in turtles and sea grass, Van Houtan and his team compared levels of arginine in tumor cells to arginine in unaffected skeletal muscle. Work said that was like comparing apples to oranges.
“If you analyze the amino acid content of an orange, it’s going to be different than an apple. You can’t say you found more amino acid in an orange and that’s causing it to be orange. It’s more complicated than that.”
Work compared the current state of research to the early years of the AIDS epidemic, when patients would appear sick with tuberculosis, meningitis or oral infections. Doctors knew their immune systems were suppressed, but not why. It wasn’t until they developed a blood test that researchers could accurately study the virus behind the symptoms. Researchers have so far been unable to come up with a blood test for the virus causing the tumors.
“Right now, we’re getting full-blown AIDS patients,” he said. Without the test, researchers don’t know if populations have the virus but no symptoms or whether turtles can be exposed and become immune.
Van Houtan pointed out that repeated studies have linked arginine to inflamed cells: “Arginine is very clearly a factor in herpesvirus replication. That’s not on the table and it is not up for dispute.”
Work also said the study did not account for the declining number of sick turtles.
“That’s the $64,000 question. I just don’t know.”
But Van Houtan insists Work is wrong about the decline. The number of turtles with tumors may be declining overall, but it is increasing in the number of locations, he said. And looking at overall numbers fails to address risk factors, like age, linked to specific locations.
Van Houtan also pointed out that while his research was peer-reviewed, the comments from Work and his six colleagues were not.
While the dispute has some scientists taking sides, Cauley believes it could kick-start research on a problem that has so far been understudied and underfunded. Cauley has long thought temperature played a part in the virus, given its concentration in warm waters, and believes scientists will eventually find more evidence that rising sea temperatures and pollution act as triggers.
“It points out the realities of what we’re having to manage now,” he said. “This is a punctuation mark as to where we are with the health of our oceans.”