Red Tide Returning to Southwest Florida

by SC Reporter Reese Holiday

Along the coasts of Southwest Florida, red tide is being pushed and pulled by a calm rhythm of waves. Barely seen but so often felt, a single cell won’t do much, but pairing it with millions of others can cause grave concern.

“This little single cell by itself doesn’t do much, but when you get the concentrations that we’re getting where it’s visibly showing up, what happens is they produce a toxin and together that toxin gets into the food web,” said Eric Milbrandt, the Sanibel-Captiva Conservation Foundation’s Marine Laboratory Director.

The microscopic organism that blooms into red tide, called Karenia brevis, was found in Sanibel by the SCCF Marine Lab on Dec. 14, which was then reported by the Santiva Chronicle. The lab reported red tide counts as high as 21 million cells per liter at Gulfside City Park Beach, potentially causing harm for both humans and sea life.

According to Milbrandt, high concentrations of red tide, which is 1 million cells per liter or more, can cause respiratory problems for both fish and people. For humans, breathing in toxins released into the air by red tide can cause short-lived respiratory irritation. For fish, they experience similar problems in the water, but the result for them often ends up being fatal.

“In high concentrations, just like for people, it causes respiratory irritation for fish,” Milbrandt said. “It’s actually a neurotoxin that stops the gills from being able to function properly, so the fish basically suffocates.”

To track the severity of red tide, people can use the Red Tide Respiratory Forecast online tool that shows where the worse spots of red tide are. However, the problem for fish can persist even with red tide out of the water. According to SCCF Marine Lab Research Scientist Rick Bartleson, red tide can linger within an ecosystem as animals consume other animals with red tide in them, transferring the toxins to the consumer.

“It gets into the whole food web and then it stays in the food web for quite a while,” Bartleson said. “That’s the type of affect it has, causing a very wide range of ecosystem problems.”

Bartleson added that red tide is very good at finding the nutrients it needs to survive, something that humans often contribute to. He said red tide feeds and grows off of nutrients like nitrogen and phosphorus, which can be found in lawn fertilizers and septic tanks. Whenever rain hits a fertilized lawn and runs off into the ocean, or whenever sewage water is dumped into that same place, nutrients stream into the ecosystem worsening the red tide.

“We’ve just been loading up the system with nutrients for too long, and we’re not slowing down at all,” Bartleson said.

Even with help from human behavior, the location, harmfulness and size of the red tide can change daily. According to Bartleson, the conditions have to be right in order for red tide to be prevalent. From the position of the current to the number of tropical storms, the conditions need to be favorable in order for it to cause problems, which doesn’t always happen.

“It starts in low numbers near the bottom of the water column, then it has the conditions that are right offshore, which depend on a certain amount of calm conditions and a certain rate of nutrient supply,” Bartleson said. “Some years, it gets exactly what it needs and some years the conditions aren’t right.”

Red tide is not an uncommon phenomenon, but rather something that happens every year. Bartleson said Karenia brevis is always found in the ocean, but human behavior can accelerate it to the point where it becomes harmful. While the severity of red tide can change year to year, even hour to hour, it leaves the struggling ecosystem in a constant loop.

“We’re stuck in a loop of going from a system that’s partially recovered to one that’s destabilized and out of control, and it keeps doing that over and over,” Bartleson said. “It’s an ecosystem out of balance, and it gets thrown out of balance every year or two at least so it never has time to fully recover.”

Bartleson added that this year’s red tide has been worse than the average year, and there’s no telling how long it will last. Reducing the use of fertilizers and finding new ways to run the sewage system could help turn it back to the less harmful natural event that it was. But with no slowdown in sight from human behavior, red tide will continue to be a problem for the waters of Southwest Florida.

“There are very few years where you don’t see anything at all,” Milbrandt said. “Some people would say that maybe it’s part of the natural ecosystem here. That may be true, but it’s been made worse by people.”