Other Life Forms

Red Tide Karenia brevis

Red tide is a HAB, or a harmful algal bloom, of small planktonic organism called Karenia brevis. This organism produces a toxin that affects the central nervous system of fish so that they are paralyzed and cannot breathe.

Red tide algae reproduce in dense concentrations called "blooms", which are visible as discolored patches of water, often reddish in color, and are characterized by a weak, ammonia-like odor. Red tide blooms often result in thousands of dead fish washing up on Gulf beaches.

Red tide is a natural phenomenon not caused by humans. When temperature, salinity, and nutrients reach certain levels, a massive increase in K. brevis occurs. No one knows the exact combination of factors causing red tide, but some experts believe high temperatures combined with a lack of wind and rainfall are usually at the root of red tide blooms. There are no known ways that humans can control it, however many scientists around the world are studying red tide.

It's important to remember that red tide has happened before and the Texas marine environment has always recovered.

Texas red tides have occurred from August through February. They typically begin offshore in the Gulf of Mexico and are transported by currents and winds toward shore. The blooms mainly come up along Gulf beaches and less frequently into bays and estuaries. It's almost impossible to say exactly where the red tide is at any given moment, because blooms constantly expand and contract and move around in response to winds and tides.

It's important to realize that red tides are typically isolated patches that don't blanket every stretch of beach. The often concentrate around wind- or tide-protected areas like man-made jetties.

It's usually okay to eat fish, crabs and shrimp during a red tide bloom, because the toxin is not absorbed into the fleshy tissues of these animals. However, you should never eat fish found sick or dead--something other than red tide may have effected them. The Texas Department of Health may issue shellfish closures banning the consumption of oysters, mussels and clams for parts of the coast, because red tide can be absorbed into their edible parts resulting in neuro-toxic shellfish poisoning. Although not known to be fatal, neuro-toxic shellfish poisoning can cause dizziness, nausea, and may last for several days.

The Texas Department of Health may issue health advisories warning beach-goers that red tide algae in the water or ocean spray can irritate your lungs, nose, and throat and may cause coughing spells. Symptoms usually disappear very soon after leaving the red-tide affected area.

Texas Parks and Wildlife has set up a menu item on its main information line to provide regularly updated reports on the current red tide even. Phone 1-800-792-1112, press 4 for fishing, then 9 for red tide information. Or call the Texas Parks and Wildlife Kills and Spills Team at (512) 389-4726.

Last updated: September 7, 2016

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