December 14, 2016
Study said no red tide this year. Here’s what went wrong, but the science is still right
When a local university’s study predicted that red tide wouldn’t infect our shores, a collective sigh of relief could be heard up and down the coast.
No canceled trips to the beach. No stinky dead fish. No burning eyes or hacking up a lung.
But we all know how this story ends. Like a jinx, the toxic algal bloom clutched the coasts of Pinellas down to Charlotte for three months. When we thought it was going away for good, it came back like a boomerang. Even last week, Longboat Key still had a high concentration of red tide that it just can’t shake.
So what happened?
Don’t start pointing pitchforks at the scientists just yet.
“The one constant about science is surprise,” said Robert Weisberg, a professor of physical oceanography at the University of South Florida. He studies the physics of ocean circulation.
In June, he and a team of researchers with USF’s College of Marine Science and the Florida Fish and Wildlife Conservation Commission published two studies in the Journal of Geophysical Research: Oceans.
Red tide, a phytoplankton with the scientific name Karenia brevis, is naturally occurring; we just don’t notice it until its in irritatingly high concentrations, killing marine life and affecting our well-being.
Weisberg said scientists understand that red tide slowly blooms anywhere between 25 and 50 miles off the coast. When it’s circulated on the bottom of the ocean and gets to the shore through a process called upwelling, other plants will out-compete the red tide in low enough concentrations.
There’s also naturally occurring nutrients deep in the ocean that ride the same circulation system. Lots of natural nutrients mean other plants can compete and no red tide that year, they predicted. Deficiencies in the natural nutrients brought on red tide.
By using 24 years of satellite data to look at the height of the ocean and therefore how deep it is, the researchers built a model to accurately predict when red tide would come to the west coast of Florida. Out of those 24 predictions, they were only wrong five times.
Four of the predictions said red tide would come when it actually didn’t, Weisberg said. This year was unique for a number of reasons.
The season for red tide typically runs from late summer to early fall. In 2015, the season extended and came back in April 2016.
That was just the beginning. Hurricane Hermine brought a lot of rain, which then created a “wall” in the Gulf of Mexico because of the density difference between freshwater and saltwater.
“If you have a sharp change in density, they tend not to mix,” Weisberg said. “Material tends to concentrate along these fronts.”
While the red tide built up, a lot of sewer systems along the coastline were overwhelmed and dumped waste into the Gulf, which was a feeding frenzy for the toxic phytoplankton to gain strength. The perfect storm of mingling conditions led to red tide hitting the coast hard.
“It’s coincidental that it was about a week after Hermine that we really started to see the red tide cell counts,” Weisberg said. “There’s no conclusive proof that one led to the other, but it looks that way.”
Weisberg said he plans on using this model again next year, adding that it’s like predicting the weather. The formative time for red tide is late spring into early summer, so the team should predict if red tide will doom us in 2017.
“It’s a complex system. We try to simplify it as best we can,” Weisberg said.
One thing that’s missing is continuous monitoring of red tide’s growth offshore, which he said there’s the ability to do so, just not the funding and support.
“I can predict the ocean circulation pretty well,” he said. “If I know what’s in the water, then I can predict when that will erupt near shore.”
A lot is still unknown about red tide, but more observations and studies can only bring more understanding about the phytoplankton, meaning more accurate predictions and, hopefully, more beach days.
“It’s all one big related problem and I know that the biology is controlled to a very large degree by the movement of the water and what the water carries with it,” he said.