The Deadly Toll of the Red Tide

They come in staggering, looking depressed. Sometimes they have ulcers on their eyes or in their stomachs.

Dr. Heather Barron’s patients range in size from sanderlings, tiny birds that can weigh as little as 3 1/2 ounces, to loggerhead turtles that weigh hundreds of pounds. And the unusually long red tide hitting Sanibel Island in Florida has kept them coming in.

The Clinic for the Rehabilitation of Wildlife has seen a 25 percent increase in patients compared with this time last year, said Barron, the medical and research director. The clinic’s staff has been stretched thin, working 80-hour weeks to treat the large number of animals left sick by the red tide.

“There’s no doubt this year has really been difficult,” said Barron, who has had one day off in six weeks.

In southwestern Florida, a toxic red tide that has lasted for about 10 months continues to show up in high concentrations along coastal counties, and tons of dead marine life have been removed from shores as a result.

Sea turtles and manatees, whose diets expose them to the toxic algae, known as Karenia brevis, are just a couple of the species with vulnerable populationsthat have been affected by the harmful algal bloom. The algae can cause respiratory irritation in humans.

Red tide is a naturally occurring algal bloom that was seen in southwestern Florida as early as the 1700s. It typically appears in late summer or early fall and subsides before the following summer. At high concentrations, the bloom can color the water with a brown or red hue.

But this year’s red tide has been unusually long and strong, said Allen Foley, a wildlife biologist at the Florida Fish and Wildlife Conservation Commission. It’s the longest one since 2006, when a red tide lasted 17 months. Scientists generally agree that algae blooms are becoming worse, intensified by agricultural runoff and warm weather.

Two sea turtle species taking the brunt are the loggerhead turtles, which are threatened, and Kemp’s ridley turtles, the most endangered sea turtles in the world. Some green turtles have also been killed by red tide.

The number of sea turtles found killed, injured or sick since November hit a high for a single red tide, at 354, Foley said.

“Events like this red tide just remind us the turtles are under a lot of pressure,” he said.

And officials are taking measures to protect other marine life.

On Thursday, the conservation commission announced a catch-and-release-only order through Sept. 26 for redfish and snook from Anna Maria Island in Manatee County to Gordon Pass in Collier County, citing the devastation to the fish populations by the red tide.

Manatees, whose calm presence has become part of southwestern Florida’s identity, have also been hit hard. Preliminary numbers identify as many as 115 manatees killed this year by red tide as of Monday, compared with 67 for all of 2017, according to Martine deWit, a veterinarian at the Marine Mammal Pathobiology Lab, which is part of the conservation commission.

The question, she said, is whether the number of manatees killed by red tide is higher in part because the manatee population is increasing.

Manatees, which are listed as threatened, feed on sea grass, which holds in the toxins, exposing them to red tide sickness even months after the bloom subsides, she said.

“When beaches clear and people stop feeling the effects,” she said, “it’s still possible for manatees to continue to be poisoned by red tide.”

Larry Brand, a professor of marine biology and ecology at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, said red tides were about 15 times worse than they were nearly 50 years ago.

This year’s red tide, he said, is exacerbated by human-based nutrients, the amount of which continues to grow as the coastal area becomes more developed. Discharge from Lake Okeechobee, where the water has high concentrations of phosphorus and nitrogen from fertilizers, has also led to an unusually large blue-green algal bloom.

“The large increase in runoff this year led to the red tide getting pretty bad,” he said.

For Barron and her staff, the weeks have been long, and she said they keep hoping the red tide will clear up soon.

The beaches of Sanibel Island have been cleared not only of people, she said, but also of wildlife. There were days previously when she saw as many as 30 ospreys. Now, it has been weeks since she spotted one.

“This time it’s just not going away,” she said.