Wind and currents push thousands of dead fish together in a massive fish kill during the red tide bloom off the coast of Sanibel, Florida, 8 August 2018. Photo: Ben Depp / National Geographic

By Maya Wei-Haas
8 August 2018

(National Geographic) – The first thing you notice is the smell. It’s not a scent, exactly, but a tingling in the nose that quickly spreads to the throat and burns the lungs. But then you see the carcasses.

Thousands of sea creatures now litter many of southern Florida’s typically picturesque beaches. Most are fish—mullet fish, catfish, pufferfish, snook, trout, grunt, and even the massive goliath grouper. But other creatures are also washing ashore—crabs, eels, manatees, dolphins, turtles, and more. It's a wildlife massacre of massive proportions. And the cause of both the deaths and toxic, stinging fumes is a bloom of harmful algae that scientists say is the region’s worst in over a decade.

“It's just like a ghost town,” says Heather Barron, head veterinarian at Florida’s Clinic for the Rehabilitation of Wildlife (CROW). “Anything that can leave has, and anything that couldn't leave has died.”

Many organisms around the world can cause these harmful algal booms, which are also known as red tides for their common rust-red color. In Florida, the culprit is usually the tiny, plant-like alga known as Karenia brevis, which produces toxins, dubbed brevetoxins, that cause both gastrointestinal and neurological problems when eaten. The latest bloom now stretches around 100 miles along the coast and miles offshore, often pushed into concentrated patches by winds and currents.

Red tide in the Gulf certainly isn't new, with reports as far back as the 1500s when Spanish explorers documented what seemed to be K. brevis-like fish kills and irritating fumes. But this latest event has turned into an algal nightmare, causing many to question the reasons behind such an intense bloom, and whether humans might be to blame. There are no easy answers, scientists say, and many researchers are split on the culprits.

The algae began coloring southwest Florida’s waters in October 2017, picking up intensity in recent months. Now residents are entering the tenth month of the bloom with no end in sight.

Background K. brevis concentrations usually fall below 1,000 cells per liter. Yet in recent counts, many sites tip the scales at over 10 million cells per liter, says Richard Bartleson, a biologist at Sanibel-Captiva Conservation Foundation (SCCF), who has been monitoring the bloom's intensity. In select spots, he's seen counts up to 140 million cells per liter.

Animals accidentally ingest the algae while feeding, which makes them “almost comatose,” says Gretchen Lovewell, program manager for Mote Marine Laboratory’s Stranding Investigations Program. “Their flippers will just be dangling there,” she says of rescuing the few live stranded turtles. But most, she says, are already dead.

This dead loggerhead is just one of a record number of turtle deaths during the ongoing Karenia brevis algae bloom in southern Florida, 8 August 2018. Wildlife ingests the toxin, which attacks their nervous system with often fatal results. Photo: Ben Depp / National Geographic

Since the beginning of the year, 80 manatees have washed ashore, all suspected victims of brevetoxin. Last week, to scientists’ surprise, a 26-foot-long juvenile whale shark was even swept onto Sanibel Island's coast, its muscles rife with algae toxins. Turtles have also been hard hit; hundreds have been killed this year. Many are the critically endangered Kemp's Ridley sea turtles.

To make matters worse, Florida isn’t just suffering from red tide. The inland waterways are clogged with yet another bloom of vibrant green cyanobacteria. Runoff from cattle farms and residential developments that lie north of the state's largest freshwater body, Lake Okeechobee, carries in nutrients, turning its waters into a thick green smoothie.

Development and sugar farms south of the lake prevent the natural trickling and filtering of overflow through the Everglades. Instead, to prevent flooding of nearby towns, heavy rains force engineers to release polluted water into the estuaries that lead out to the sea. The problem has worsened in recent years—and solutions are mired in politics.

“There's just dead fish everywhere,” says local resident Tammy Hodgson, who has lived in south Florida for 25 years. There's some hesitation to spread information about what's going on for fear of further impacting local business, she explains, but something must be done. [more]

Red Tide Is Devastating Florida's Sea Life. Are Humans to Blame?

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