TAMPA — In October 2012, Florida’s southwest coast was painted red by the tide; dead fish washed ashore, manatees died by the hundreds and sun worshippers wheezed and hacked away on the beaches.
Red tide had come ashore, and scientists said it was the worst assault on the senses and the ecosystem in five years.
This year, red tide, known in scientific circles as Karenia brevis, is absent from beaches ranging from Pinellas County to Charlotte Harbor, areas where it usually is pushed ashore by wind and tide.
Could it be that the algae bloom skipped the region because marine scientists from all over the nation are attending the seventh annual National Harmful Algae Symposium this week in Sarasota?
More likely, the reasons are natural.
“How blooms form initially is really a complicated question that investigators are trying to figure out,” said Nadine Slimak, director of communications for the Mote Marine Laboratory in Sarasota, which keeps a close eye on red tide movements each year and monitors 25 beaches along the coast. Mote offers twice-a-day online updates.
“Florida generally does have a red tide every year,” she said. “But whether it affects the coastline depends on currents and where the bloom is moving.”
The timing is just right for the symposium, where some 215 researchers from 31 states are meeting to discuss harmful algae blooms across the United States. Red tide gets a good share of the focus.
The event, co-sponsored by Mote Marine and the Florida Fish and Wildlife Conservation Commission, is a chance for scientists and public health experts to share their latest research in the field.
Still, even with all the top minds in the nation there, red tide — how it blooms and gathers steam and where it goes — remains somewhat of a mystery, said Alina Corcoran, a research scientist in charge of the fish and wildlife commission’s Harmful Algal Bloom program.
“There are remaining questions of what makes it start,” Corcoran said. Once the bloom is out there, prevailing currents can be used to predict where it’s going.
Red tide blooms typically start in the late summer to early fall, but they can occur at any time, she said.
Physical qualities in the Gulf of Mexico affect if and when blooms occur, she said. Typically the algae bloom occurs 20 to 40 miles offshore and is a natural occurrence.
“What is different this year compared to last is the circulation of the Gulf,” Corcoran said. “This year it did not favor early bloom initiation. We have documented very low to low concentrations of red tide in Southwest Florida. We are monitoring and will continue to monitor near-shore and coastal waters.”
If it stays out in the Gulf, no one notices, she said. If it moves onshore, it’s a big deal.
So far this year, she said, only “blips” of red tide have shown up on the shores of Southwest Florida.
“That could mean that something may be brewing,” she said. But not likely.
At least it won’t be like last year.
Beginning in October 2012, the coast of Southwest Florida was inundated by a 100-mile-long bloom of red tide that made landfall between Bradenton and Port Charlotte. Scientists said the outbreak compared with the 2006 bloom that for months left fish belly-up on beaches. Beachgoers also suffered with watery eyes, irritated noses and scratchy throats.
The algae also took its toll on other species. Birds that ate fish succumbed to the toxins. Sea turtles and manatees, which do their breathing just inches from the water’s surface, also took a hit last winter. A record number of manatee deaths were reported this year, with one-third of them attributed to red tide.
Though last year’s version was bad, it was worse during a record red tide that began in January 2005 and lasted until February 2006.
Robert Weisberg, a professor of physical oceanography with the University of South Florida’s College of Marine Science in St. Petersburg, thinks he has documented a phenomenon that may explain why some years are red tide heavy and some aren’t.
Weisberg theorized that an unusual “strong and persistent upwelling of nutrient rich water” from the deep portions of the Gulf of Mexico plays an integral part. He said such a phenomenon favors conditions for a faster-growing type of algae called diatoms over the slower growing red tide algae, which effectively blocks out massive red tide blooms.
The same conditions were present in 2010 when red-tide incursions were nearly nonexistent, he said.
“Similar conditions occurred this year,” Weisberg said. “I predicted the absence of a large red tide bloom occurring this year when I began to notice the similar conditions developing late last spring.”
There’s more to red tide than red tide itself, he said.
“From these physical oceanographic explanations, one must appreciate that red tide ecology is not just biology,” Weisberg said. “Instead, red tide ecology — like anything ecological — includes all factors that influence how an organism makes its living.”
There’s another byproduct of this upwelling of nutrient rich seawater, he said.
“The same process,” he said, “is what likely accounts for the fact that grouper fishing has been so good near shore this year.”