Gulf of Mexico Harmful Algal Bloom FAQs

NOAA's Harmful Bloom Operational Forecast System (Gulf of Mexico HAB Forecast)

NOAA's Gulf of Mexico HAB Forecast provides information and operational forecasts regarding the potential development, intensification, transport and associated impacts of harmful algal blooms of Karenia brevis (commonly known as red tide) in the Gulf.

The forecasts are communicated through the Gulf of Mexico Forecast website. The Respiratory Forecast provides an assessment of the risk for respiratory irritation associated with a K. brevis bloom at individual beaches, every 3 hours out to 30 hours. The likelihood of intensification of the bloom at the beginning of the bloom season is provided by the Intensification Forecast. Information regarding the location and extent of the bloom, and abundance of cells at individual sampling locations are provided on the Satellite Imagery page. For more detailed information about the website, please visit the Gulf of Mexico Forecast Guide.

Respiratory Irritation Forecasts

The respiratory irritation forecasts are issued every 3 hours out to 30 hours into the future.

Respiratory irritation impacts are forecasted in levels ranging from "very low" to "high" (in addition to "none" or "not expected") based on wind direction and speed, as well as the nearby algal cell concentrations identified in water samples. The "very low" respiratory irritation level affects only people with severe or chronic respiratory conditions. Similarly, the "low" respiratory irritation level affects people who are otherwise healthy, but are more sensitive to Karenia brevis aerosols. The "moderate" respiratory irritation level indicates that the general public may potentially notice mild respiratory symptoms, while the "high" respiratory irritation level is likely to affect most of the general public with adverse respiratory symptoms (NOAA, 2013). Refer to the table below for more information about the respiratory impact levels. See below for forecast region maps.

Affected Population
None Chronic
Sensitive General Public
None X      
Very Low   X    
Low   X X  
Moderate   X X X
High   X X X

Harmful Algal Bloom & Karenia brevis (Red Tide) Basics

A "red tide" is a common term used for a harmful algal bloom. Read more from the National Ocean Service Ocean Facts here.

To learn more about why harmful algal blooms occur and the research that is being done, visit the National Ocean Service Ocean Facts here.

Harmful algal blooms of Karenia brevis (red tide) are common in the Gulf of Mexico, occurring nearly every year along the Gulf Coast of Florida and with increasing frequency along the coast of Texas. The blooms occur more often late in the year, typically starting between August and October and ending between December and February. The presence and duration of blooms, their intensity, and the extent of the area impacted by the bloom varies significantly from year to year. Blooms can last a few weeks, months and sometimes over a year. Typically a harmful algal bloom only affects small portions of the coast for short periods of time.

In Florida, blooms more frequently form offshore of the southwest coast of Florida between Tampa Bay and Naples. Occasionally a harmful algal bloom that formed offshore the west coast of Florida is transported to the east coast by ocean currents. Every few years blooms may also form offshore the Florida Panhandle. In Texas, blooms are most frequently reported in the Port Aransas and South Padre Island regions.

For information about historical bloom records in Florida, visit the Fish and Wildlife Research Institute's HAB Monitoring Database webpage, which includes a table of the years and months with confirmed and suspected red tide along the west coast of Florida from 1844 through present.

Not all areas of the coast are equally affected during a red tide. HABs are generally isolated patches that are transported by winds and currents. The blooms are patchy in nature and the impacts vary by location and throughout the day depending on nearby bloom concentrations, ocean currents, surf conditions, and wind speed and direction. Check NOAA's forecasts for help finding an unaffected coastal area.

Karenia brevis HAB (Red Tide) Impacts & Health Questions

In the Gulf of Mexico, one of the most common HABs is the phytoplankton species Karenia brevis. Commonly known as red tide, this organism produces a toxin called brevetoxin that can cause respiratory irritation in humans, contaminate some shellfish, and affect the central nervous system of fish , marine mammals, and birds, potentially causing fish kills and marine mammal death.

When Karenia brevis cells near the ocean surface are broken up by surf at the shore or by breaking waves offshore, the toxin produced by K. brevis can become airborne and incorporated into the marine aerosol, or sea spray. Onshore winds can blow the airborne toxins onto the beach, potentially causing eye and respiratory irritation (coughing, sneezing, tearing, and itching) to beachgoers. Onshore winds and currents can also transport fish killed by exposure to the toxin onto the beach. Respiratory irritation in humans is significantly reduced when the winds are blowing offshore. Any effects usually decline when a person is no longer exposed, and wearing a particle mask can reduce irritation for some people. People with severe or persistent respiratory conditions (such as chronic lung disease or asthma) may experience stronger adverse reactions and should avoid red tide areas.

State authorities monitor the levels of K. brevis and when cell concentrations reach a predetermined level, are required to put a shellfish ban in effect stating that it is not safe to harvest mollusks (e.g., clams and oysters) and gastropods that feed on bivalves (e.g., whelks). These notices are available from the Florida Department of Agriculture and Consumer Services and the Texas Department of State Health Services. More information about shellfish harvesting and consumption during a red tide is provided below.

For more information regarding Karenia brevis and their impacts in the Gulf, refer to the Gulf of Mexico HAB Forecast Health Information Page.

It is not recommended to swim in or around K. brevis blooms because the toxin can cause skin irritation, rashes and burning and sore eyes, 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. For more information on the health effects of K. brevis blooms refer to the Florida Department of Health.

Commercial seafood available from local restaurants and seafood dealers are strictly regulated and regularly tested for safety.

Always check on the status of shellfish (clams, oysters, mussels) harvesting areas before engaging in recreational shellfish harvesting or consuming shellfish that were harvested recreationally. Cooking and/or freezing does not destroy the Karenia brevis toxin.

According to the Texas Department of State Health Services and Florida Fish and Wildlife Research Institute, it is usually okay to eat fish, crabs, lobsters, and shrimp during a Karenia brevis bloom because the toxin is not absorbed into the fleshy tissues of these animals. This advice is based on the assumption that only the "edible" portions are being consumed (the fillet or muscle). Scallops are also safe to eat as long as you only eat the muscle of the scallop and not the whole animal.

Oysters and other shellfish, such as clams, mussels, and whelks, can accumulate Karenia brevis toxins in their tissues. People that eat oysters or other shellfish containing red tide toxins (brevetoxins) 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 or months. Toxins are heat resistant, so cooking infected shellfish will not remove or deactivate the toxins.

For more information on Karenia brevis blooms and their impacts in the Gulf, refer to the HAB Forecast Health Information webpage. For additional Health and Safety information, visit the FWRI and Texas Parks and Wildlife Department (TPWD) Health Information FAQs.

Additional Information

To Report Suspected Illness Related to Aquatic Toxic Exposures or Harmful Algae:
Poison Control Center: (800) 222-1222

For K. brevis HAB Status Updates:
Fish and Wildlife Research Institute: (866) 300-9399; callers from outside Florida dial (727)552-2448

To Report Dead Fish:
Fish and Wildlife Research Institute (FWRI) fish kill hotline: (800) 636-0511; submit a fish kill report online here.

Additional Resources:
Florida Department of Health: (850) 245-4299
Florida Department of Health, Public Health Toxicology Section: (850) 245-4401

For K. brevis HAB Status Updates
Texas Parks and Wildlife (TPWD) hotline: (800) 792-1112, select "fishing" and then "red tide"

For Current Information about Shellfish Closures:
Texas Department of State Health Services Seafood Safety Division: (800) 685-0361

To Report Fish Kills and Discolored Water:
During normal business hours, call your local TPWD office or (361) 825-3244; outside of normal business hours, call TPWD's 24-hour communications centers at (512) 389-4848 (Austin) or (281) 842-8100 (Houston)

Kirkpatrick, B., L.E. Fleming, D. Squicciarini, L.C. Backer, R. Clark, W. Abraham, J. Benson, Y.S. Cheng, D. Johnson, R. Pierce, J. Zaias, G.D. Bossart, and D.G. Baden. 2004. "Literature Review of Florida Red Tide: Implications for Human Health Effects." Harmful Algae. Volume 3. Pages 99 to 115.

Kusek, K.M., G. Vargo, and K. Steidinger. 1999. "Gymnodinium Breve in the Field, in the Lab, and in the Newspaper - A Scientific and Journalistic Analysis of Florida Red Tides." Contributions in Marine Science. Volume 34. 229 pages.

Lansberg, J.H. 2002. "The Effects of Harmful Algal Blooms on Aquatic Organisms." Reviews in Fisheries Science. Volume 10, Number 2. Pages 113 to 390.

NOAA. (2013). NOAA Harmful Algal Bloom Operational Forecast System (HAB-OFS). Retrieved February 8, 2013, from CO-OPS HAB-OFS.

Steidinger, K.A., G.A. Vargo, P.A. Tester, and C.R. Tomas. 1998. "Bloom Dynamics and Physiology of Gymnodinium breve with Emphasis on the Gulf of Mexico." In Physiological Ecology of Harmful Algal Blooms. Editors D.M Anderson, A.D. Cembella, and G.M. Hallegraeff.

Stumpf, R.P., M.E. Culver, P.A. Tester, M. Tomlinson, G.J. Kirkpatrick, B.A. Pederson, E. Truby, V. Ransibrahmanukul, and M. Soracco. 2003. "Monitoring Karenia brevis Blooms in the Gulf of Mexico Using Satellite Ocean Color Imagery and Other Data." Harmful Algae. Volume 2. Pages 147 to 160.

Stumpf, R., Tomlinson, M., Calkins, J., Kirkpatrick, B., Fisher,K., Nierenberg, K., Wynne, T. (2009). Skill assessment for an operational algal bloom forecast system. Journal of Marine Systems, Pages 151-161.

Tomlinson, M.C., R.P. Stumpf, V. Ransibrahmanakul, E.W. Truby, G.J. Kirkpatrick, B.A. Pederson, G.A. Vargo, and C.A. Heil. 2004. "Evaluation of the Use of SeaWiFS Imagery for Detecting Karenia brevis Harmful Algal Blooms in the Eastern Gulf of Mexico." Remote Sensing of Environment. Volume 91. Pages 293 to 303.