Scientists fear red tide bloom may be lingering offshore

Drunk-acting cormorants are showing up in higher numbers at a Sanibel rehabilitation center, and the birds are testing positive for a toxin related to a harmful algal bloom festering in the Gulf of Mexico. 

A patch of red tide off Boca Grande, near Lee County's northeast border, is visible by satellite and is moving closer to shore, scientists say. 

The combination of satellite imagery and sick birds has local water quality scientists concerned that a red tide could soon move into the area. 

Red tide lingering, aimed at Lee

These aquatic birds are the canary in the coal mine for detecting red tide, an algal bloom that causes fish and marine mammal kills and can cause respiratory issues in humans. 

"We definitely started to see an uptick in October, which is sort of the official start of red tide season," said Heather Barron, hospital director at the Center for the Rehabilitation of Wildlife, or CROW, on Sanibel. "I think it’s possible they were locally exposed."

Red tide (Karenia brevis) is a naturally occurring microorganism that can turn deadly if concentrations become too high. Blooms typically start off the coast of Sarasota and work their way south. 

The Florida Fish and Wildlife Conservation Commission tracks red tide blooms and  Friday reported higher concentrations off Sarasota and Manatee counties. 

"It makes sense because that's where we're seeing the higher counts," said Tracy Fanara, with Mote Marine Laboratory in Sarasota. "We’re preparing for a bloom at this point."

Booming red tide bloom lingering in Gulf

Red tide is measured in cells per liter. Concentrations of up to 1,000 cells per liter are harmless, but fish kills can start when numbers reach 10,000 cells per liter or higher. 

Counts along the Southwest Florida coast range from safe background levels to upwards of 100,000 cells per liter. 

Samples in Lee County inshore waters have tested clean in recent weeks. 

"This week — partly because (Dr. Barron) has seen more cormorants — we started bringing in more samples," said Rick Bartleson, a water quality scientist for the Sanibel-Captiva Conservation Foundation. "On Wednesday we got a lot of samples inshore and I didn’t see any in Pine Island Sound but we haven’t gotten around to the beach samples That’s more likely where we’ll see it first."

Blooms aren't just harmful for the marine ecology. 

"Red tide can aerialize and move onshore and cause respiratory issues even in healthy people," Fanara said. "Usually if you leave the beach, if you don’ t have asthma or a respiratory illness, you are fine, but if you do the symptoms can last up to seven days."

Barron said it's practically impossible at this point to tell exactly where the birds were exposed to the red tide toxin. 

"Algae can be anywhere: it doesn’t just bloom at the surface," Barron said. "It can bloom below the surface, sometimes fairly low down. (And) they’re birds, they can fly anywhere."

Connect with this reporter: Chad Gillis on Twitter.