The red tide dinoflagellate Karenia brevis. Public Domain, photo by Florida Fish and Wildlife Conservation Commission
Last week as I sat in a beach-side open-air restaurant in southwest Florida, I started coughing. Hard. I couldn’t stop, and I apologized repeatedly. Yet I hadn’t felt sick before, and the suddenness of the coughing was very weird.
Our waitress came by as I was expressing my bewilderment. She said, “Oh, it’s the red tide.” She said she had coughed all day too, and that some people were more sensitive than others (many people in the restaurant seemed unaffected), and that all that was necessary to relieve the symptoms was to go inland.
I stared out at the darkening Gulf of Mexico. A strong breeze blew into my face. Was this really possible? Was the irritation in my throat and my unstoppable coughing really the result of a microscopic sea creature? I had never heard that red tide could affect people on land. Since the algae that cause red tide, in spite of their menace, are still algae, and therefore a topic near and dear to my heart, I had to know what was going on.
After doing a little digging, I discovered I had indeed had an unexpected run-in with Karenia brevis (see here for pretty pictures), a dinoflagellate* that is the Gulf of Mexico’s very own purveyor of red tide neurotoxins.
Dinoflagellates are two-tailed plankton. They are also protists, the loose association of single-celled organisms with DNA inside nuclei and cellular organelles that are usually much bigger than bacteria or archaea. About half are predatory, half make their own food, and obviously, now we know some do both. The photosynthetic lot are the second most abundant constituent of the photosynthetic marine plankton after diatoms (which I covered here).
So, it is worth emphasizing, most dinoflagellates don’t cause red tides, nor are they inherently evil. Even Karenia, which does cause red tide, is not an infectious organism. It’s photosynthetic and makes its own food. It only causes problems when dies or gets eaten.
This is the very real result. This video was taken in October just miles north of where I was last week (warning: graphic decay images):
During my stay, on the beach I saw dozens of dead horseshoe crabs, brittle stars (some still alive), crab bits, and a few fish washed ashore after a storm.These were also likely red-tide casualties.
The chemical that made me sick and killed all these fish and crabs is a neurotoxin called brevetoxin. Here’s Brevetoxin A, which, you must admit, is quite beautiful:
A deadly neurotoxin, or the Very Hungry Caterpillar? YOU decide.
When fish eat Karenia, they may accumulate this toxin in their bodies. When enough has accumulated, they die, but before that happens, they may in turn be eaten by a bottlenose dolphin or manatee. These, too, have been fatal victims of red tides. Shellfish also accumulate brevetoxin from Karenia they eat, and unfortunate diners who consume them in turn may acquire Neurotoxic Shellfish Poisoning, a charming combination of nausea, vomiting, and slurred speech.
K. brevis that die near shore or get smashed to bits in the surf somehow have their brevetoxins aerosolized, possibly carried on bits of sea salt or dust. When blown ashore, they can cause a suite of symptoms called “Red Tide Tickle” by tongue-in-cheek locals. For those of us who are sensitive, they include watering eyes, sore throat, and uncontrollable coughing. These effects stop pretty quickly once you get out of the breeze. The symptoms may be worse and far more prolonged in asthmatics, and may even contribute to more pneumonia, bronchitis, and asthma-related ER visits, if this 2009 study in Environmental Health Perspectives is to be believed. All told, the respiratory effects of red tide in Florida may cost up to $4 million a year. Some people report that swimming in red tides can cause irritated skin, too. I recommend you Don’t Try That at Home.
To me, it wasn’t especially, and it probably isn’t to most tourists. I left the restaurant and went home. The coughing stopped as soon as I got out of the sea breeze, and my sore throat was gone by morning. But I can’t help but think about that poor waitress — stuck there for an entire shift, all day every day she works, in red tide or no. For her, as for the fish and mammals of southwestern Florida waters, there is no easy escape.
*Dinoflagellate literally means “whirling scourge”, and if you watch one, it’s easy to see why. Here is a video of a dinoflagellate waving one flagellum and twirling its other, inexplicably paired with Billie Holiday. The flagellum twirling and Billie Holiday are both cool, I just don’t get why they go together.