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Living and fishing with red tides.

Anglers in parts of Florida--the lower Gulf Coast, especially--are familiar with the short-term consequences of red tides, including fish kills.

But what exactly is red tide?

For starters, red tide is not red, and it's not a tide. Red tide is an algae bloom, a localized explosion in the population of a single-celled microscopic dinoflagellate. In Florida the outbreaks usually consist of clouds of a critter called Karenia brevis. It's called "red" tide because in extremely high concentrations the red tide organisms can color the water rusty, though even the most severe red tide events do not turn the water truly red, and in most blooms the water is never discolored at all. The "tide" portion of the red tide moniker comes from the fact that red tide, like anything else suspended in the water, can be swept into (or away from) an area on the tide.



Red tide organisms cause problems for fish because they emit chemicals called brevetoxins which interfere with the functioning of gills. You can examine a sample of coastal sea water almost any time and find a few red tide critters, but when the population skyrockets, the amount of brevetoxin in the water can become high enough to kill fish. Decomposing fish float to the surface and can be carried by wind and tide to create those stinking piles of carcasses which headline the news stories which usually follow.

Humans are affected by red tide too, but in a different manner. Red tide toxins become airborne due to the wash of breaking waves or the wakes of passing boats. Airborne brevetoxins can cause scratchy throats, coughing, and red, watery eyes. Some people are more sensitive to red tide than others, but a severe red tide outbreak is unpleasant for everyone.

A few observations about red tide: First, a pile of thousands of fish corpses is a sobering sight, but the impact on local fish populations is usually not as bad as people think when they see the carcasses. Fish stocks can be depleted locally, but mother nature never kills all the fish and they will come back.

Fish that sense red tide may not bite for days at a time, so if you can't catch anything in your favorite spot when red tide is nearby it doesn't necessarily mean that all your fish have died.They may simply be laying low until conditions improve.

Second, fish floating dead at the surface does not mean that there is active red tide in the area. Dead fish often drift for miles from the location of their demise and the water might be fine under those rotting corpses. Conversely, water can look perfectly normal while harboring fish-killing levels of red tide. Lastly, red tide is not a "yes" or "no" thing. Blooms vary greatly in intensity, with many outbreaks never reaching levels which are lethal to wildlife.

Red tide is a natural phenomenon which has been documented in Florida's waters for hundreds of years. Like most natural processes, red tide comes in cycles. Sometimes years will pass between significant outbreaks, and sometimes the blooms occur one after another. Several seasons can pass during which minor red tide blooms occur that never reach severe levels, then the cycle can shift and it seems as if every bloom reaches fish-killing and beach-clearing levels. Much progress has been made in recent years in tracking red tide blooms and in monitoring impacts on fish and on beachgoers, but scientists are still unable to predict when outbreaks will occur or how severe they will become or how long they will last. Adding to the difficulty in tracking red tide is that conditions can quickly change, sometimes entering or leaving an area in a matter of hours. The current status of red tide blooms can be viewed at redtide/events/status/statewide/.

There is a raging debate as to whether human activity has affected the red tide cycle. Many people believe that the runoff of fertilizers and other chemicals into coastal waters has caused red tides to become more frequent and more severe, but scientists who have researched decades of red tide history have thus far been unable to document any change in red tide patterns that's attributable to human causes. Whenever a severe red tide outbreak creates piles of dead fish and sends throngs of tourists fleeing the beaches there is an outcry for "something" to be done to make the red tide go away. Unfortunately it seems unlikely that humans will ever be able to chemically control blooms that can spread across hundreds of square miles of ocean, and even if we could, it's not clear that we should. It's possible that red tide, a natural process that has existed for centuries, plays some not-yet-understood and important role, perhaps similar to the cleansing and rejuvenating effects of wildfire on woodlands.
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Publication:Florida Sportsman
Geographic Code:1U5FL
Date:Mar 1, 2014
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