What it is and why you should avoid going near it

A type of microscopic algae called Karenia brevis has grown rapidly in Florida, leaving dead fish on the shore.

A type of microscopic algae called Karenia brevis has grown rapidly in Florida, leaving dead fish on the shore.

The noxious “red tide” is wreaking smelly havoc on Florida’s Gulf Coast, canceling spring break for some beachgoers, causing eye burns and respiratory irritation in humans, and killing wildlife.

Over the past few weeks, a type of microscopic algae called Karenia brevis has been growing rapidly there in what is commonly known as the red tide, due to the way harmful algal blooms change the color of ocean water.

These blooms develop offshore and are brought closer to land by currents and winds, usually from upwelling nutrients from the ocean floor. And they don’t just happen in Florida; red tides can occur in oceans around the world, and as a result of other types of algae as well, although those caused by K. brevis are particularly harmful to humans and animals.

There is no certain answer as to when this latest Florida red tide event will end. “If we’re really lucky, it will fade or die in the next few weeks,” said Richard Stumpf, an oceanographer with the National Oceanic and Atmospheric Administration, or NOAA, who studies harmful algal blooms. “If we don’t have that chance, it may last longer.”

Since red tide conditions can change from day to day, it’s important to stay informed if you plan to spend time on the water or at the beach, wherever you are. Here are some answers to common red tide questions:

What causes red pipe?

Red tides occur naturally and have been documented around the Gulf of Mexico specifically since the 1500s, said Richard Pierce, an ecotoxicologist at the Mote Marine Laboratory in Sarasota, Florida.

Algal blooms caused by K. brevis in particular require a complex variety of factors aligning at the right time.

“The first is biology – the organism must be present in the water and it must out-compete other phytoplankton,” Mote Marine Laboratory explains on its website.

“The second is the correct chemistry – this includes the correct temperature, salinity and nutrients it needs to grow and multiply. The third element is the right physical conditions to concentrate and transport K. brevis. The fourth element is l Ecology – the presence or absence of other life forms, such as other seaweeds, which may encourage or inhibit K. brevis blooms.

When these conditions are ripe, the blooms hit and the K. brevis organisms multiply out of control.

Nutrient-laden runoff from sewage and fertilizer spills doesn’t cause a red tide, Pierce said, but it can intensify it. “If the red tide is in the area, it will make the situation worse and make it last longer,” he said.

How long does the red tide last?

Typically, harmful algal blooms form in the fall and can last anywhere from a few weeks to more than a year, Pierce said.

“The duration of a bloom in coastal Florida waters depends on the physical and biological conditions that influence its growth and persistence, including sunlight, nutrients and salinity, as well as wind speed and direction and water currents,” says Florida Fish and Wildlife. Conservation Commission, or FWC.

A bloom will eventually “die out” if the water is colder, the red tide disperses, and the bloom is moved to an area with fewer nutrients it needs to reproduce, Pierce said.

A red tide in 2021 in Xianglu Bay in China.

A red tide in 2021 in Xianglu Bay in China.

A red tide in 2021 in Xianglu Bay in China.

Can the red tide make you sick?

Harmful algal blooms have been reported in all US coastal states. Those caused by K. brevis are concentrated in Florida and Texas around the Gulf of Mexico, but they have also been found along the Atlantic coast to North Carolina.

K. brevis red tides are a big problem not only because the reddish-brown water looks unpleasant; algae can also be toxic to humans and wildlife. K. brevis produces tasteless and odorless neurotoxins called brevetoxins that can become airborne and cause eye and respiratory tract irritation in humans.

You don’t even necessarily have to go into the water to be affected. Just being outside near a red tide can cause symptoms.

“If I go out to the beach with it, I feel like I’ve suddenly caught a cold. My nose is runny. I have a cough. My eyes are crying. My sinuses hurt sometimes. I will leave the beach, [and] 15 minutes later, I’m fine,” Stumpf said.

“People with asthma are at risk of greater health risks,” he added, noting that anyone with chronic obstructive pulmonary disease should also be careful about exposure.

If you are affected by red tide, Florida poison control centers recommend moving indoors to an air-conditioned room to relieve discomfort and seeking medical attention if your symptoms are more severe. Stumpf noted that wearing a mask can also help mitigate the risks of inhaling patenttoxins.

For animals, exposure to brevetoxins can be deadly, which is why red tides often produce smelly heaps of dead fish on the shore. Patentoxins paralyze the gills of fish, killing them, Stumpf said. “The toxin, if ingested in sufficient quantity, can kill birds and mammals,” he added. This month, a manatee was rescued in Florida due to distress caused by the red tide.

Can we eat fish and seafood during the red tide?

Neurotoxins produced by K. brevis can accumulate in shellfish and cause neurotoxic shellfish poisoning if ingested.

But Stumpf said that as long as you’re buying seafood from a reputable dealer and not out of the back of someone’s truck, it’s safe to continue eating fish and shellfish because the industry is tightly monitored.

“Commercially available shellfish are often not harvested locally and, if harvested locally, are tested for red tide toxins before being sold,” the FWC notes.

Can pets go out where the red tide happens?

With pets, it is better for their health to keep them away from a red tide.

“They are like people. If they’re along the beach when the wind is blowing on shore, they’re inhaling the neurotoxins, and that’s not good for them,” Pierce said.

Also watch out for foam that builds up on the beach during red tide, as it can be rich in toxins.

“A lot of times dogs will lick a possibly dead fish, lick the moss, and they can get very sick. And in fact, they can die from it,” Pierce said.

I’m planning a beach vacation. How far in advance can we predict the red tide?

Red tide events have seasonal patterns. “If you want to avoid the red tide, generally vacation time [in Florida] would be May, June, July, August,” Pierce said. “Statistically, blooms would start in September-October and last all winter, then taper off in late April.”

But if you’re planning vacation weeks in advance, be aware that it’s not yet possible to predict exactly when and where the red tide may impact certain beaches. Your best bet is to consult meteorologists and meteorologists for up-to-date information on red tide concentrations.

The FWC, for example, publishes regular updates on red tide conditions based on K. brevis sampling. NOAA also predicts potential respiratory irritation at individual beaches in Florida and Texas, based on field samples of K. brevis concentration and factors such as wind speed.

Stumpf said wind direction can also help determine if it’s safe to be on shore.

“YYou could be on the beach and never notice it. I had lunch on a beach during a strong red tide and had a wonderful lunch as the wind blew the toxin over the gulf, not inland,” he said.



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