local links page.
Discolored water and dead fish in the Gulf of Mexico indicated something was mysteriously wrong. The date of this observation was 1530 aboard a Spanish vessel. This is the first reported incident of what may have been red tide in the gulf. We've had over a dozen blooms in Texas the last 60 years. Most of them have been minor compared to those in 1935 and 1986. The first documented Texas outbreak was in 1935 when a massive fish kill accompanied an aerosol that caused coughing, sneezing and watery red eyes in September off Corpus Christi. The fish kill associated with that incident was much greater than the 1986 occurrence which is estimated to have taken over 22 million fish. In 1935 people speculated the dead fish and noxious gases were the result of an underwater volcano in the gulf. It was not until 1947 when scientists figured the event was caused by a small single cell microorganism or dinoflagellate called Gymnodinum breve. When conditions are right, it can multiply to enormous numbers sufficient enough to discolor water, kill fish and release an irritating aerosol into the air. The organism is one of two species that cause red tides in Texas waters but the only one that produces an aerosol.
G. breve (hereafter referred to as red tide) is about one one thousandanth of an inch in diameter with 2 whiplike appendages called flagella that propel and spin it through the water. It has chlorophyll like a plant so it can manufacture its own food using sunlight. The cells reproduce by dividing and they can duplicate every two days. Ideal conditions for reproduction are warm water, sunlight, calm seas, oceanic salinities and nutrients such as nitrogen and phosphorus along with certain trace elements like iron and manganese.
Scientists believe the red tide is always present offshore in the gulf and currents play a significant role in transporting it to coastal waters off Florida and Texas, the two gulf states which most often experience blooms or dramatic increases in numbers. Sonia Gallegos a researcher with the Naval Research Laboratory at Stennis Space Center in Mississippi believes Texas blooms result from a jet current created by two counter rotating currents in the gulf. These are like underwater hurricanes (but turning much slower) which rotate and push water toward our shores in the Fall, bringing up nutrients and possibly resting stage cysts of red tide from the bottom resulting in a bloom. Regardless of the theory most researchers agree that blooms begin offshore and less often in our bays. Also, these particular blooms are not thought to result from nutrients in runoff.
However, even the cyst stage is highly debated. Don Hockaday, acting director of the UT Pan Am Coastal Studies Lab on the island and I did document a lone bay bloom which killed thousands of menhaden that washed up on the north shore of Port Isabel September 25, 1995. Could this have resulted from dormant cysts? No offshore blooms had been reported that year.
One thing we are sure of is the red tide resulting from this small microorganism has a definite impact on fish and people. This is because of a neurotoxin present in the cells called brevetoxin which is actually a soup of five different toxins. When red tide cells burst in surf or over a fishes gills, this toxin is released and available for uptake into a fishes bloodstream via gills, or into the air via water particles (aerosol) released by waves. In a fish the toxin is deadly and cell concentrations of 250 cells in one milliliter (1/30 of an ounce) of water kill fish. Wave action, wind and cell concentrations determine the strength of the aerosol and its effect on people. Concentrations of 400 per milliliter in heavy surf with moderate wind can be just as irritting as cell counts of 40,000 cells per milliliter in light surf. and little wind.
People with asthma should avoid the aerosol since their condition can be aggravated. Contact dermatitis has been reported as a symptom of exposure to red tide. Sore throat, coughing, sneezing and watery or itchy eyes are the most common symptoms.
Brevetoxin does not affect shrimp and crabs, and these can be eaten by humans without any problems. Also fish caught in red tide water can be safely eaten. The same it not true for oysters, clams and mussels which are filter feeders that can concentrate the toxin and cause neurotoxic shellfish poisoning when eaten by humans. Symptoms are hot and cold reversal, nausea, dizziness, tingling sensations in the extremities and dilated pupils. One case of respiratory failure has been reported. The toxin can remain in these bivalves for up to two months. For this reason the Texas Department of Health closes any Texas waters to the taking of bivalves if counts exceed 5 cells per milliliter and the waters stay closed for a period after the bloom dissipates to allow the toxin to clear.
Cell counts regardless of their numbers do not affect hatching of redfish eggs but red tide is lethal for larval redfish. A 21 day old fish can survive 1000 minutes in a cell concentration of 25 per milliliter and 100 minutes in 2000 cells per milliliter. Larry McEachron- Science Director for the Coastal Fisheries Division with TPWD says a bloom in 1996 caused an impact on Aransas and Corpus Christi Bays' larval redfish. He said "the recruitment index was much below the long term average". According to McEachron, redfish have been spawning since mid September and TPWD should know what the impact will be by February when they accumulate and assess bag seine data.
Probably the heaviest losses resulting from the bloom are in dollars to tourism.
Karen Steidinger with the Florida Department of Natural Resources has been studying red tides in Florida for several decades and she suggests that 20 to 40% of their primary production comes from the red tides. She says large bloom usually results in a good shrimp crop the following year. Since our major shrimp species is different from Floridas' we have not seen that impact. We still don't know the actual cause of the red tide, we can't predict the severity, duration or occurrence but we do know what it is, and that is more than Spaniards knew in 1530 and Texans knew in 1935.
Comments/questions to E. Anthony (Tony) Reisinger
last update 16 Oct 2000 hockaday@panam.edu)