Many coastal Panhandlers woke up this week to the sight and smell of dead fish. Thousands of them washed ashore from Panama City to Pensacola. This mass die off included a variety of species including whiting, sheepshead, hake, cusk eels, and even lionfish; there were also reports of dead bass from the Dune Lakes in Walton and Okaloosa counties. What caused this mass die off of fish?
The suspect is red tide…
Most of us along the panhandle have heard of red tide but we may not know what it is or what causes it. Many attribute the red tide events to human impacts, stormwater runoff etc., but in fact they have been around for centuries. There are records suggesting that the European colonials experienced them and I have read one account that the Red Sea got its name from the frequency of these events there. So what is this “red tide” and what causes it?
It is actually a bloom of small single celled plants called dinoflagellates. There are thousands of species of dinoflagellates in the world’s oceans and not all cause red tide, but there are several species that do. These small microscopic plants drift near the surface of the ocean acquiring sunlight to photosynthesize. They possess two small “hairs” called flagella (hence the name “dinoflagellate”) to help orient themselves in the water column. Most have a shell covering their body called a theca and some shells have small spines to increase their surface area to resist sinking. One method of defense found in some dinoflagellates is the production of light – bioluminescence. This light is produced by a chemical reaction triggered by the creature as a flash of blue – many locals refer to it as “phosphorus”. Other dinoflagellates instead will release a toxin… some of these are ones we call “red tide”.
Red tide organisms are always in the water column of marine environments but are usually in low concentrations, maybe 300-500 cells per milliliter of water. But under favorable conditions, warm water with nutrients, they multiple… sometimes in great numbers, such as 3000-5000 cells/ml, and we have a “bloom”. The number of cells within these blooms can be high enough that we can actually see the water change color… hence “red tide”.
The most common red tide dinoflagellate associated with the Gulf of Mexico is Karenia brevis. Karenia blooms typically form offshore and are of little impact to the coastal communities. However when the wind and tides are right these blooms will drift towards shore. When they do fish kills occur and humans have eye and throat irritations. Marine mammals in particular struggle with red tide. As the bloom comes near shore it reaches the bottom of the water column and many of the bottom dwelling fish suffer. Most of the photos of fish I saw in the October 2015 fish kill were bottom dwellers, including many invasive lionfish.
Is there anything we can do to prevent red tides?
Not really… Again, they are naturally occurring event. We may increase the frequency of the events by discharging excessive nutrients into the water from our run-off but they would probably occur anyway. Red tide events are not as common in the panhandle as they are in southwest Florida. The Gulf waters near Charlotte Harbor are shallow, warm, and near the many manicured lawns, gold courses, and the discharge of much of the agriculture in the state. Occasionally blooms formed in that part of the state drift north but this year a bloom formed off of Bay and Gulf counties in early October. The recent storm that passed through probably pushed the bloom inland and to the west. The biggest hazard of humans is eye, throat, and skin irritation. It is quite uncomfortable to be around these blooms. In 1996 a local bloom was concentrated enough that the campground at Ft. Pickens had to be closed. I was in Galveston Texas when I heard about the red tide occurring in the Florida panhandle. As I was leaving Galveston the newspaper reported the closer of all oyster harvesting in Texas due to a red tide generated in the Padre Island area and was moving north. Seems that red tide is covering a large portion of the Gulf coast the last week of October. That said… anything communities can do to reduce nutrient runoff will certain decrease the frequency of red tides.
The Florida Fish and Wildlife Conservation Commission post red tide updates from around the state on their website and the Escambia County Extension Office post a local water quality update each Friday that has red tide information as well.
Escambia County Extension