SARASOTA — Red tide algae can take a toll on the future of the stone crab industry, Mote Marine Laboratory researchers discovered.

Intense concentrations of the toxic red algae potentially can wipe out a generation of stone crabs, Mote scientists reported this week.

The loss could be cataclysmic to Florida's seafood industry. The health of stone crabs is commercially valuable to the health of Florida's economy.

More than 105 million pounds of stone crabs were harvested between 1996-2016 and is ranked fifth by the National Marine Fisheries Service among the commercially harvested Florida seafood. Pink shrimp ranks number one. Nationwide, Florida's seafood industry ranked 11th in the United States, producing more than 87 million pounds of seafood harvested in 2016 and with a dockside value of $237 million, Marine Fisheries reported.

Mote scientists are trying to help figure out why the stone crab catch in Southwest Florida has seen a 25 percent decrease since 2000, and trying to determine the influence of red tide could be a key.

High concentrations of Florida red tide — Karenia brevis — caused 100 percent mortality in stone crab larvae in a four-day study, Mote reported in a press release. Medium concentrations had a 30 percent mortality rate, and many of the surviving larvae had impaired swimming behavior.

“We found that Florida red tide toxins, known as brevetoxins, can be lethal to larval stone crabs in their earliest developmental stage, or they can have ‘sub-lethal’ effects that don’t kill the larvae but impede their normal behavior,” said Mote researcher Dr. Phil Gravinese. “The severity of these effects appears to depend on the concentration of red tide algae and duration of the exposure.”

Researchers published the results of their study in the peer-reviewed, scientific journal Harmful Algae.

Among the results, researchers determined how within 48 hours of exposure to a "high-toxin strain" of the algae, 93 percent of the stone crab larvae died. Exposure to low concentration didn't affect mortality rates.

“Our previous research suggests that sublegal stone crabs, whose claws are nearing legal harvest size, have a short window of tolerance for elevated concentrations of Florida red tide algae and begin to die off when that window is exceeded,” said Mote researcher Phil Gravinese in a prepared statement.

“This is one possible way that red tide might reduce the catch rate," Gravinese said. "Alternatively, severe and prolonged blooms that overlap with the crabs’ summer reproductive season might be reducing the number of offspring, or larvae, that are available to recruit into the fishery.”

State support

Mote's research into the impacts is just beginning. Working hand-in-hand with researchers at the Florida Fish and Wildlife Conservation Commission, state legislators approved the Florida Red Tide Mitigation and Technology Development Initiative involving $3 million annually for six years to sustain FWC and the nonprofit Mote lab's red tide research.

The bill has passed all its legislative hurdles and is now waiting to be brought to Gov. Ron DeSantis for his signature. With the governor's signature, the bill can be implemented July 1.

"It turned our area upside down," said State Sen. Joseph Gruters, R-Sarasota, of the 2017-18 red tide bloom that killed millions of fish and other sea life up and down Florida's West Coast. Gruters' district includes Cape Haze and portions of Charlotte County, which endured blooms that lasted longer than most areas of the state, although red tide was reported as far away as the Florida panhandle coast and even the Atlantic coast.

Gruters and Rep Ed Hooper, R-Palm Harbor, whose district includes coastal areas of Pasco and Pinellas counties, sponsored the original bill. Among the goals, Gruters said, is to encourage integrated and coordinated research efforts.

"It will buy dividends in the future," Gruters said.



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