A toxic “red tide” has been affecting Florida beaches since last year, and is especially bad right now. Our friends at Earther are covering the subject in depth, but if you’re perplexed about what a red tide is and why everyone is talking about it, we have answers to your basic questions.
A “red tide” is actually a bunch of microscopic creatures floating in the water. The ocean is always full of microbes, but when we talk about a red tide we’re thinking of certain species that sometimes appear red and can fill the water with their naturally-produced toxins. The red tide in Florida is the work of a species called Karenia brevis.
Each individual K. brevis is a single cell, with a little tail that it uses to swim. It can make food from sunlight, like plants do, so it’s considered a type of algae. And because it’s a tiny living thing in the ocean, it’s also a type of plankton. K. brevis is a brownish color under the microscope, but when seawater is full of them, we can see the water as tinged with red—or sometimes yellow or brown.
Other, harmless algae can also turn water interesting colors, so instead of “red tide” it’s considered more precise to talk about a “harmful algal bloom.”
An algal bloom is a large population of algae—bajillions of the tiny creatures filling up the seawater in a particular area. When conditions are right, including plenty of nutrients in the water, algae reproduce. Imagine if every time you walked into an all-you-can-eat buffet, you could just have a bunch of babies so that your whole family could overrun the restaurant and devour everything inside.
K. brevis blooms in the ocean every year, and washes up on Florida’s Gulf Coast shores. It’s not the kind of bloom that’s associated fertilizer runoff—that’s the other bloom affecting Florida right now (yep, they have two). But the red tide bloom might be feeding on the other one, and fertilizer might play a role. That said, it’s usually other factors, including ocean currents, that make red tides bloom in Florida’s waters each year. K. brevis thrives on carbon dioxide and enjoys warm water, so climate change may be part of why this year’s bloom has gotten especially bad.
This year’s bloom started last October, and didn’t clear up this spring like the blooms typically do. There’s a good chance it will get worse from here, since red tide season is starting up again.
K. brevis makes a neurotoxin (a poison that affects the nerves and brain) called brevetoxin. This toxin can kill animals, including fish and birds. Manatees and sea turtles have also turned up dead during the recent red tide.
People who eat shellfish contaminated with the toxin can get neurotoxic shellfish poisoning, so it’s important not to collect or eat shellfish from an area affected by red tide. The toxin is odorless, colorless, and tasteless, and it’s not destroyed by cooking. Symptoms include nausea, vomiting, and diarrhea, and a tingling or numbness in the face, hands, and feet.
We can also breathe the toxin. When algae-filled waves crash on the beach, they can break apart some of the algae’s cells and send their toxins into the air. People with asthma or other lung conditions are most at risk, but healthy people can be affected too. The symptoms you would notice are difficulty breathing, and perhaps eye irritations as well.
Beaches affected by red tide will often post a sign that warns about breathing the air in the area, especially if you have lung conditions like asthma. The water may be full of dead fish, so it’s not like you wanted to swim there anyway.
It’s too early to say for sure, but NBC reports that many areas have seen a decrease in the amount of K. brevis in water samples. It’s possible that the hurricane mixed up the ocean water “like a blender,” diluting the red tide organism, according to one biologist they spoke to.
On the other hand, flooding that results from hurricanes can push nutrients into the sea for K. brevis to feed on. Smithsonian reports that red tide increased after four hurricanes hit Florida in 2004, but also that Hurricane Katrina was followed by a decrease in red tide. So we’ll have to wait and see.