Red tide: What you need to know

Reporter: Stephanie Byrne
Published: Updated:

Fast Facts:

  • Karenia Brevis is the organism that forms red tide.
  • Experts say red tide begins naturally; However, human activities have the potential to influence red tide.
  • Red tide is poisonous to wildlife and can be deadly.
  • ‘Brevetoxin,’ which is found in red tide, is what causes people to cough and have respiratory irritation.
  • The ‘brevetoxin’ is not known to be linked to neurological diseases in humans.

Red tide has become part of life living on the Gulf Coast. You may associate it with either rust-colored water, coughing, or dead fish washing ashore. We talked to experts from UF/IFAS Extension-Charlotte County and the Sanibel-Captiva Conservation Foundation (SCCF) to better understand it.

Betty Staugler is the Florida Sea Grant agent for UF/IFAS Extension-Charlotte County, as well as the Harmful Algal Bloom Liaison for NOAA’s National Centers for Coastal Ocean Sciences. Staugler explained red tide is a type of algal bloom. She said, “It’s caused by a specific type of algae called a dinoflagellate. There are about 2,000 of them worldwide. Most of them are completely harmless and they actually produce most of the Earth’s oxygen, so we think of them as good things, however, some of them can be toxic and red tide is an example of a dinoflagellate that is toxic.”

She also tells us red tide has been documented for hundreds of years, and while it may seem like red tide is worsening, “What we recognize as scientists in the records is over time, we’re not comparing apples to apples and that’s because the effort in monitoring red tide has not been consistent over time and so since 1996 or so is when we really started ramping up the monitoring of red tide and so if you go back beyond that, you can’t really compare and say that we have more incidents.”

On the other hand, she went on to say, “However, in many blooms, in particular, the cyanobacteria blooms, we do have evidence that they are increasing as climate is changing and waters are warming because many algal species respond to warmer temperatures and higher nutrients, which kind of goes hand-in-hand with warmer temperatures. Red tide is a little bit different because it’s what we would consider to be more ecologically flexible. It doesn’t respond as well to these warm climates. It doesn’t, you know, it responds to many different nutrient sources and so it’s just kind of a different beast, but there is, you know, if we’re seeing other algal species increasing and there is some relationship between them and we don’t understand that yet, then it’s possible we could see increases in red tide blooms.”

Red tide can be patchy in nature. For instance, beachgoers can visit a beach free of red tide, even when red tide is somewhere off the coast. Dr. Rick Bartleson, SCCF research scientist, said, “There are parcels of water that don’t easily mix, so sometimes there are very distinct patches. Currents and eddies can also concentrate red tide into patches.”

He also said it is possible for some years to be worse than others.

“Some years the conditions are just right for the patches to form, and some years there are better conditions for growth. The Loop Current, hurricanes, upwelling, hundreds of metric tons of phosphorus in storm runoff, can all contribute. A good year would be when wind patterns and storms prevented dense patches from forming offshore, and then when small patches arrived at the beach, winds from a strong cold-front push the patches south toward the Gulfstream,” Bartleson added.

These algal blooms are also naturally occurring, beginning tens of miles offshore in usually nutrient-poor waters; However, nutrients from land can help charge red tide.

Staugler said a frequent question is whether or not the activities on land influence the red tide blooms. She says, “…yes they do. We know that Karenia can take advantage of at least 13 different nutrient sources and the land-based nutrients are one of those 13 sources. It is not the biggest, most significant source, but it is a contributing source. So it’s not what starts a bloom, but once that bloom moves into nearshore waters, it can take advantage of anything we put into our estuaries and onto the coast,”

Another big concern with red tide is the health effects on humans and wildlife. In regards to animals, Dr. Bartleson explained, “The toxins it produces are very poisonous, and affect the nervous system. Fish are exposed through their gills, but can also get a stomach fill eating the red tide cells or eating other sea life that had consumed red tide. The food web gets contaminated, including seagrass blades, so birds, sea turtles, and manatees can be affected. When any algal bloom happens, the oxygen can be depleted from the water column and some benthic creatures can suffocate.”

But what about humans? You may have experienced it yourself: You’re on or near a beach and you begin to cough. It’s actually because of a toxin called “brevetoxin.” Staugler said, “This brevetoxin is actually a neurotoxin, so it’s affecting the neurological system and it can become aerosolized, so when the cells die, they break open. This can happen just because of wave action or because it’s the end of their life or because they reach salinity conditions that they can no longer live in. Those cells break open and they can actually become attached to water vapor and become airborne, if you will, and be carried a mile, maybe even two miles, depending on the wind conditions and that brevetoxin actually causes people to cough. It’s that irritation.”

For most people, once they leave the area, they’re fine; However, Staugler tells us, “For people who have respiratory illnesses such as asthma or COPD, it can actually have lingering effects, so we always ask those people to avoid beaches when there is an active red tide occurring on the beach because they could be exposed to those brevetoxins.”

While some studies link blue-green algae toxins to neurological diseases, Staugler said brevetoxin is not known to have the same effect. She also said if a human were to eat shellfish exposed to red tide, that person could become very sick.

As red tide is naturally occurring, we’re told there isn’t really a way to prevent it; However, there are ways to prevent fueling it. Dr. Bartleson said, “We don’t know exactly how much that will help, but when a patch runs out of nutrients, it will senesce.” He went on to say, “Besides reducing septic tank waste, sewage discharge, fertilizer, fallout from burning sugar cane, manure from half a million cattle, there’s not a lot we can do. Maybe storing rainwater in wetlands and uplands so it doesn’t wash tons of nutrients and organic matter into the estuaries. Abiding by the Clean Water Act and Wetlands Protection Act would help. And reducing carbon emissions. The extra CO2 is appreciated by phytoplankton, as, to some degree, the warmer ocean.”

MORE: Click HERE for SCCF Red Tide Resources

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