Red Tide: Frequently Asked Questions
Information courtesy Texas Parks and Wildlife Department © 2004
Original article published here.
- What is red tide?
- What causes red tide?
- How, when and where do red tide blooms start?
- Where is the red tide on the Texas coast right now?
- How can I get the latest information on the current red tide?
- Should I consider postponing a trip to the coast right now?
- Is it safe to eat fish that I catch in or near the red tide?
- Why doesn't the state post signs on the beach warning the public about red tide?
- Is it safe to eat oysters during a red tide?
- Where can I get more information on red tide?
Red tide is a naturally-occurring, higher-than-normal concentration of the microscopic algae Karenia brevis (formerly Gymnodinium breve).
This organism produces a toxin that affects the central nervous system of fish so that they are paralyzed and cannot breathe. As a result, red tide blooms often result in dead fish washing up on Gulf beaches. When red tide algae reproduce in dense concentrations or "blooms," they are visible as discolored patches of ocean water, often reddish in color.
Red tide is a natural phenomenon not caused by human beings. When temperature, salinity, and nutrients reach certain levels, a massive increase in Karenia brevis algae occurs. No one knows the exact combination of factors that causes 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, but many scientists around the world are studying red tide at present. 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 in the Gulf of Mexico. Currents and winds then transport blooms 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. They often concentrate around wind- or tide-protected areas like man-made jetties.
Texas Parks and Wildlife has set up a menu item on its main toll-free information line to provide regularly updated reports on the current red tide event. Phone 800-792-1112, press 4 for fishing, then 9 for red tide information. Red tide updates will also appear on the Current Status page of the TPWD web site and on the Facebook page for harmful algal blooms.
Jack Ralph, former head of the Texas Parks and Wildlife Department's Kills and Spills Team, had this to say on the subject: "If it were my family heading to the coast, I would not cancel a vacation because of red tide. It's an isolated, patchy phenomenon that does not blanket every stretch of beach. On any given day, there are generally miles of good beach and clean water for beach-goers and anglers to enjoy. However, we encourage all travelers to heed the advice of the Texas Department of State Health Services, get the current facts and draw their own conclusions, since different people have different comfort levels with these kinds of situations."
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. This advice from the Texas Department of State Health Services is based on the assumption that only the "edible" portions are being consumed (the fillet or muscle). Keep in mind that you should never eat fish found sick or dead, whether or not they are caught during a red tide.
The eye and throat irritation caused by red tide results from high concentrations of the algae and rough surf. These conditions cause the red tide's irritant to become suspended in the air in the salt spray. There is typically little or no irritation when surf conditions are relatively calm. In most red tides in Texas, these conditions vary a lot within the space of days or even hours. As a result, the same part of the beach may have irritating conditions in the morning and those conditions may be gone by afternoon. On a calm day, even with red tide in the surf zone, many people can enjoy the beach because there is not a lot of salt spray from the surf carrying irritant to the beach. The best advice for beach visitors is if they feel effects in an area, leave that area and try another one. Some local authorities will post signs on beaches that they manage. Be aware of all beach warnings when visiting the beach.
Oysters and other shellfish such as clams, mussels, whelks and scallops can accumulate red tide toxins in their tissues. People that eat oysters or other shellfish containing red tide toxins may become seriously ill with neurotoxic shellfish poisoning (NSP). Once a red tide appears to be over, toxins can remain in the oysters for weeks to months. For this reason, the Texas Department of State Health Services (TDSHS) closely monitors oyster growing areas for the presence of red tide and red tide toxins. TDSHS has the authority to close shellfish harvesting areas during and after a red tide. Oysters you buy from a restaurant or certified shellfish dealer should not have red tide toxins in them because of the TDSHS’s monitoring program. There are, however, other risks associated with bacteria and other contaminants in raw oysters. For more information about consuming oysters, consult a physician or health authorities such as TDSHS. To find more information on Vibrio vulnificus, which may be contracted by eating raw oysters, please refer to the TDSHS Vibrio Fact Sheet (PDF) and this rack card (PDF).
Call the red tide phone information line mentioned above -- dial (800) 792-1112, at the menu select fishing and then red tide.
For more information, visit:
The Harmful Algae Page - supported by a National Science Foundation/National Oceanographic and Atmospheric Administration grant to the National Office for Marine Biotoxins and Harmful Algal Blooms at Woods Hole Oceanographic Institution
The Texas Parks and Wildlife Department and the Texas Department of State Health Services investigate reports of possible red tide along the coast and in the bays.
Three common signs of a red tide bloom are:
- discolored water
- dead fish
- breathing difficulty
From the Centers for Disease Control:
The human health effects associated with eating brevetoxin-tainted shellfish are well documented. However, scientists know little about how other types of environmental exposures to brevetoxin—such as breathing the air near red tides or swimming in red tides—may affect humans. Anecdotal evidence suggests that people who swim among brevetoxins or inhale brevetoxins dispersed in the air may experience irritation of the eyes, nose, and throat, as well as coughing, wheezing, and shortness of breath. Additional evidence suggests that people with existing respiratory illness, such as asthma, may experience these symptoms more severely. Download a fact sheet.
To report sightings of red tide during normal business hours, call your local TPWD office or 361-825-3244. Outside of normal business hours you may call TPWD's 24-hour communications centers at 512-389-4848 (Austin) or 281-842-8100 (Houston.)
Although some travelers may be concerned with how the red tide may affect their vacation plans, there are miles of clean beaches to enjoy on the Texas coast. When making travel plans, heed the advice of the Texas Department of State Health Services: get the current facts and draw your own conclusions.
For more information about red tide and the latest updates, call the TPWD hotline at (800) 792-1112, select fishing, then select red tide.
Current information about shellfish closures can be obtained by contacting the Seafood Safety Division of the Texas Department of State Health Services at (800) 685-0361. The Texas Parks and Wildlife Department and the Texas Department of State Health Services investigate reports of possible red tide along the coast and in the bays.