String of small fish kills in Florida Keys ring more hot water alarms. Is seagrass next?

Will Benson, one of the top fishing guides in the Florida Keys, got an eerie feeling one day in early July on the water near Marathon.

A dead puffer fish floated dead on the surface — a small but potentially significant sign that something about Benson’s precious Florida Bay wasn’t quite right.

Benson scooped up the fish and handed it off to the scientists at Bonefish & Tarpon Trust for further study. The tiny puffer was hardly the last dead fish he would see across the Florida Keys last month.

“It’s heartbreaking,” Benson said. “Unfortunately, it seems to be a part of a new normal.”

That fish proved to be among the first sightings of what’s become a month-long string of small fish kills affecting shallow waters that run the length of the island chain, from Key Largo to Key West. Researchers blame soaring sea surface temperatures off the southern coast of Florida that have at at time approached 100 degrees and are running some seven degrees above normal.

The toll, for now, has been relatively minor, isolated to smaller fish that live in shallow water that are especially vulnerable to heat stress and low oxygen levels. The 13 species documented so far include mojarras, grunts and toadfish, according to the Florida Fish and Wildlife Conservation Commission.

Unlike coral bleaching that threatens reefs off South Florida, the scattered kills haven’t drawn much public or media attention. But scientists and fishing captains like Benson fear they could be the marine equivalent of canaries in the coal mine, a warning of potential risks to larger fish prized by Florida Bay anglers like snook, bonefish and tarpon but, more important, to the vast seagrass meadows that support them. Some are worried the lethal heat could even result in a mass seagrass die-off, which could throw the entire bay off balance for years.

Waters off Florida hit record high temps. Brace for fish kills, algae blooms, coral damage

Benson, a fishing guide of 23 years, fears another seagrass die-off could be the beginning of the end for a fishing and guiding industry that long has been a driver of the Florida Keys economy. Florida Bay in particular has been repeatedly hammered by seagrass losses, often triggered by decades of environmental mismanagement that cut off the historic flow of freshwater from the Everglades.

“If we have ecosystem failure, I’m no longer a fishing guide; I can’t pay my mortgage; the Florida Keys isn’t the Florida Keys anymore,” Benson said. “We’re in a really bad situation.”

Ironically, a string of Everglades restoration projects have helped increase the volume of freshwater and may be providing seagrass a bit of buffer, at least temporarily, during the record South Florida heat wave.

Record water temperatures

Climate scientists have reported alarmingly high sea surface temperatures in South Florida’s coastal waters. The Keys have been the hottest spot.

A July 12 reading from Garfield Bight in Everglades National Park placed shallow water at a record 98.1 degrees. Throughout Florida Bay, temperatures have stubbornly stayed in the low-to-mid 90s, and one July 24 measure from Manatee Bay, just north of Key Largo, placed the water even higher, at 101 — literally hot tub temperature.

That can be deadly for some marine life. As the ocean gets hotter, it holds less oxygen. and algae blooms are more likely, which further suck up oxygen.

Ross Boucek, Florida Keys initiative manager at the Bonefish & Tarpon Trust — a nonprofit that advocates for clean water and healthy sport fisheries — said he’s been working with fishing guides across the islands and scientists at Florida International University to track the extent of the kill.

He’s heard dozens of reports of dead fish from Key Largo all the way south to Key West, he said, ranging from one dead fish to dozens across different basins. Thomas Matthews, a program administrator for the Florida Fish and Wildlife Conservation Commission, said his agency has officially counted 24 fish kills this summer — most small in both numbers and fish size, hitting common near-shore species less able to move into deeper, cooler waters.

Though recent showers and rain storms have offered a momentary reprieve, the worry is that there are months of hot summer days ahead.

“The longer this persists, the more uncertain our fate gets in terms of what’s going to happen on the back end of this,” Boucek said. “Everyone’s on the edge of their seat and doing rain dances.”

Theresa Cody, an associate research scientist at the Fish and Wildlife Research Institute, said there’s no doubt the kills are related to conditions created by extreme heat. Algae blooms, also fueled by heat, could make things and bring far more extensive fish kills. There haven’t been any documented blooms as of late July, according to FWC’s satellite imagery, she said. But that could change.

In the meantime, marine life — including juvenile spiny lobsters that use the shallow bay as a nursery — are still struggling.

“As with all animals, fish can maintain normal physiological function only within a certain temperature range, and outside that range their body systems can’t function,” she said. “The higher the temperature, the faster the change. The longer the hot conditions last, the more difficult it is for fish to survive.”

Is seagrass next?

Scientists are also monitoring the sprawling shallow seagrass beds, known as “flats” to anglers, that are the dominant habitat in Florida Bay.

FIU professor James Fourqurean and his lab, which specializes in seagrass, is bracing for damage — if not now, then not far down the road.

“We should only expect it to get hotter, for the bay to get saltier and for oxygen problems to increase,” Fourqurean said. “If we don’t see huge seagrass die-offs this year and it stays this hot next year, there’s no reason to expect we won’t see it happen next year.”

It’s happened before — in 1987, about 60,000 acres of seagrass withered and the muddy bay bottom turned the water the color of coffee-and-cream anytime the waves kicked up. At the time, Fourqurean was a graduate student working with the Audubon Society when a fishing guide called it to his attention.

“I said, ‘It’ll blow away in the winter. Don’t worry about it,’” he said. “Man, that was wrong. The next year, it was bigger and the year after that it was bigger.”

That die-off, and others in the past, have been driven by skyrocketing salinity levels, not soaring temperatures. The bay is what scientists consider an estuary, where freshwater blends with salt water in near-shore zones. Development over the decades — most notably the construction of the Tamiami Trail — bottled up the natural flow of freshwater through the southern Glades and into Florida Bay, throwing the salt-fresh mix out of whack many years with damaging results.

Florida Bay has seen a general decline in seagrass and a fish populations that are vital to the guiding business. Some years have been worse than others. Most recently, in 2015, Capt. Benny Blanco said he nearly went under due to a mass seagrass die-off. An estimated 40,000 acres of seagrass were decimated in the bay.

Blanco, who advocates for the environment with nonprofit Captains for Clean Water, said tourism in the area took a major blow. It took years to rebuild his clientele.

“All of the older generation guys retired; the younger generation guys quit,” Blanco said. “There weren’t enough fisheries to sustain our business.”

The super steamy waters this summer are a new factor, its impacts still to be seen.

If there is positive news, it’s an increased freshwater flow through the Everglades might be the relief Florida Bay needs, said Kelly Cox, a Florida Audubon attorney and member of the Everglades Coalition, a group of environmental advocacy organizations fighting to protect a sprawling system that stretches from north of Lake Okeechobee down to Florida Bay.

Although much work remains in the multi-billion-dollar restoration effort, one project that may already be helping is the reconstruction of Tamiami Trail, which effectively acted as a freshwater dam since 1928. A series of bridges constructed along the road in the last decade have helped bring more water south — and future projects promise a far larger and regular flow of freshwater. State government has also signaled support for restoration: Florida’s latest budget, signed in June, designates nearly $700 million for Everglades efforts.

There’s a handful of other projects in progress Cox hopes will protect Florida Bay in the long term as water quality issues abound.

“Seagrasses are surviving right now,” Cox said. “But if you have those compounding stressors — continued extreme heat, algal blooms — they build off of one another, increasing the risk of ecosystem collapse. And one of our best defenses to that is Everglades restoration.”