A mysterious ailment causing fish in the Florida Keys to spin in circles has touched off a frantic race to find the cause and save an endangered species before it’s too late.
Eight months into scientists’ hunt, some think a primary suspect has emerged: Toxins from algae colonizing the seafloor may be causing neurological issues for some fish species.
Fishermen noticed the bizarre behavior in October, according to Ross Boucek, a fisheries ecologist with the Bonefish & Tarpon Trust, a nonprofit conservation and fishing group.
“When they shined their lights, fish would turn upside down and spin to the bottom,” he said.
Over the following months, Boucek received reports of upside-down stingrays and lemon sharks whirling violently in the mud. Dozens of species were afflicted, including the critically endangered smalltooth sawfish, which is known for its flat snout with teeth that looks like a saw blade.
At least 47 sawfish have died, though the number is likely higher, said Michael Crosby, the president and CEO of Mote, a nonprofit marine lab and aquarium. The toll is profound, given that there may be just several hundred of the fish left in U.S. waters.
An emergency response to rescue afflicted sawfish launched in early April, involving government agencies and nonprofit partners. Meanwhile, scientists at several laboratories are trying to figure out what’s causing the widespread distress for marine life.
Recently, researchers’ tests identified a co*cktail of natural toxins in both seawater and the tissues of some stricken fish.
“The hypothesis I’m working on at the moment is really that the combination of these various benthic algal toxins are coming together to create the phenomenon we’re seeing,” said Alison Robertson, a senior marine scientist at the Dauphin Island Sea Lab.
But that isn’t confirmation, she added, and researchers don’t know what caused the algae or toxins to proliferate. Plus, other experts are less convinced.
“I honestly don’t think anything can reasonably be ruled out right now,” Crosby said.
Whatever researchers ultimately conclude may determine what’s on dinner plates at some Florida restaurants, how fishermen make their livelihoods and whether tourists come to visit. The Keys have already suffered several ecological shocks: Hurricane Irma in 2017, record sea surface temperatures last year and the mass die-off of corals.
“We’ve been bouncing from crisis to crisis down here,” Boucek said.
Allison Delashmit, executive director of a fishing group called the Lower Keys Guides Association, said “there’s a lot at stake.”
“Our economy is built on tourism. It’s not a good look to have spinning fish on the water and broadcasting it without answers about what it is,” she said.
That puts local scientists under intense pressure to deliver answers.
Is the algae to blame?
It’s been a tiring eight months for Boucek, whose freezer at home is filled with dead fish he plans to send out for testing. He compared the effort to “a final exam you forgot about and never studied before, and you have two hours to learn everything.”
When the work began, he said, the most likely explanations for the bizarre fish behavior did not pan out. Oxygen levels in the water were normal. There weren’t any signs of red tide. Tests for pollutants found nothing out of the ordinary.
Boucek figured the exposure was likely from the water, and when he removed spinning fish from the ocean and placed them in tanks with clean water, some recovered in as little as 25 minutes.
The only lead was elevated background levels of a genus of algae called Gambierdiscus in water samples.
That clue drew the attention of Michael Parsons, a professor of marine science at Florida Gulf Coast University and an algae expert who had been collecting that very genus in the Keys for more than a decade. In February, Parsons found that levels of Gambierdiscus cells were about four times higher than he’d ever recorded.
Robertson, an environmental toxicologist, reoriented her laboratory to respond to the crisis and has been working seven days a week. She estimates her team has performed more than 5,000 analyses of algae, seawater and the muscles, livers, kidneys and stomachs from a variety of affected fish species.
Her work has turned up toxins known to affect fish behavior, as well as some new potential toxins that had never been seen before in the Keys.
“The things we’re finding in benthic algae, we’re also finding in a lot of fish samples,” Robertson said.
She suspects a “co*cktail” of toxins from seafloor algae, potentially from several species, are combining to cause the strange fish behavior, though she said there is still “no obvious smoking gun.” The toxins could be interacting with other environmental toxins too, she said.
Efforts to save the sawfish
Other scientists, meanwhile, are racing to help distressed sawfish.
In early April, Mote staffers rescued an 11-foot male sawfish that was swimming in circles in Cudjoe Bay. They loaded the fish onto a boat, brought it to a quarantine facility with clean, filtered seawater and infused it with antibiotics, lipid compounds and other treatments, according to Crosby.
“If you can put it in human terms, we had a patient brought into intensive care,” he said.
The fish stabilized and “was beginning to swim in a more natural pattern,” Crosby said.
But two weeks later, the animal’s health cratered and it had to be euthanized.
“We were clearly heading in a positive direction, but the internal organs were too far gone,” Crosby said.
He added that he hasn’t seen enough evidence to convince him that algae is to blame. Results of the necropsy (an autopsy of an animal) are still pending, but they could offer important information because researchers were able to run tests shortly after it died. Mote also plans to try to rescue more sawfish.
There are other reasons for hope, too.
Robertson said this episode does not seem to represent the crash of an entire ecosystem.
Other important species are doing OK, including barracuda, bonefish and tarpon, which seem to be largely unaffected, Boucek said.
Florida lawmakers have also agreed to spend $2 million on fish research in the Keys, which could help scientists reach answers more quickly.
“Because so many scientists are coming together on this issue, we’re going to be able to work out what’s going on and find mitigation strategies and solutions,” Robertson said.
Evan Bush
Evan Bush is a science reporter for NBC News. He can be reached at Evan.Bush@nbcuni.com.
