Harmful red tide bloom spreads along Southwest Florida coast

A red tide bloom that's lingered since October has spread out along the Southwest Florida coast in the past few days and is expected to drift further south, toward Collier County and the Florida Keys.

The latest Florida Fish and Wildlife Conservation Commission report shows background to medium concentrations of red tide (caused here by Karenia brevis) in Sarasota, Charlotte, Lee and Collier counties.

The bloom has recently been strongest along the Lee County coast, and fish kills have been reported at various area beaches.

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But it's spread in recent days, and the University of South Florida College of Marine Science predicts the bloom will move inshore slightly before moving further south in the next few days.

"We’ve also seen it inside Pine Island Sound," said Rick Bartleson, a water quality scientist at the Sanibel-Captiva Conservation Foundation on Sanibel. "It’s spread from the northern section near Captiva down here to Tarpon Bay, and we had high (1 million cells per liter and higher) concentrations in Tarpon Bay these last few days. It’s pretty visible."

Dead mullet is a sign that the bloom is close to shore and in local bay waters. Mullet will actually eat red tide, which is one reason they're often found during fish kills.

Recently larger fish like black and red drum have been washing up on local beaches, which is an indication that the bloom is off the beaches.

Marco Island is the southernmost spot the bloom was located in the latest report, but it's shown up in Florida Bay and the Keys in recent months.

Although red tide typically forms off the coast of Sarasota, this one seems to have formed off Lee County.

Fish kills reported in the past week in Lee County were from the following locations: Big Carlos Pass, Big Hickory Island, Bonita Beach, Captiva, the Causeway Islands, Fort Myers Beach, Gasparilla Island, Lighthouse Beach, Little Hickory Island, Lovers Key State Park, Newton Park, San Carlos Bay, Sanibel Island and offshore of St. James City.

Collier fish kills were reported from: Barefoot Beach, Delnor-Wiggins Pass State Park, Doctors Pass and Vanderbilt Beach.

Besides dying fish, breathing irritation was reported this week in Southwest Florida.

Tracy Fanara, staff scientist at Mote Marine Laboratory and Aquarium in Sarasota, said respiratory issues were reported Thursday in south Lee and north Collier.

More: Red tide exploding off Lee beaches

More: Red tide counts exploding along Southwest Florida coast

She said predictions from the National Oceanic and Atmospheric Administration, or NOAA, show red tide lingering in the air in both counties through at least early next week.

"I was really disappointed that the bloom came back, and I’m not seeing any kind of prediction from NOAA or any weather event that would cause anything to change between now and Monday," Fanara said.

Fanara said people exposed to red tide have varying reactions. Some people are more sensitive to the toxins produced by blooms.

"They might have itchy eyes or a runny or itchy nose, but the more obvious is the consistent coughing," Fanara said. "It’s almost like a dry cough. It’s almost like you have no idea why you're coughing. The toxin is causing the sodium channels in your respiratory system to close, and that makes you cough."

Red tide occurs naturally at background levels in the Gulf of Mexico but blooms to harmful levels when conditions are right. Blooms have been recorded for more than a century, but scientists think nutrients running off the Florida landscape increase the frequency and duration of these events.

Warm temperatures can contribute to the blooms size and intensity, and waters were an unseasonably warm 70 degrees off Fort Myers Beach Thursday, according to the Sanibel-Captiva Conservation Foundation.

A mild cold front is working its way through the region this week but isn't expected to significantly drop water temperatures.

Fanara said people with asthma and other breathing difficulties should avoid beaches when red tide is prevalent.

"It can be very serious, that's why it’s important to inform the public about the conditions," she said. "They can feel the effects of red tide for days or even weeks."

Connect with this reporter: Chad Gillis on Twitter.

Red Tide

Red Tide (Karenia brevis) in cells per liter:

0 to 1,000: background levels with no impact anticipated

1,000 to 10,000: possible respiratory irritation, shellfish harvesting closures

10,000 to 100,000: Respiratory issues, possible fish kills and bloom chlorophyll likely detectable by satellites at upper limits

100,000 to 1,000,000: All the above plus discoloration of water

Source: Florida Fish and Wildlife Conservation Commission