An unusually persistent harmful algal bloom (red tide) affected portions of the coasts of Florida between 2017-2018, dissapating in the winter of 2018/2019. It persisted on the southwest coast beginning in October 2017 and spread to the Panhandle and the east coast of Florida. A short-lived bloom also occurred in Texas in September, 2018. Red tides, caused by Karenia brevis algae, produce toxins that can cause fish kills, respiratory irritation, and mortality of sea turtles, manatees, birds, and dolphins. For the latest updates, visit the Florida Fish and Wildlife Conservation Commission's red tide status website, the Texas Parks and Wildlife's red tide status website, or the NOAA Harmful Algal Bloom Bulletin. The following is an archive of questions and answers related to this bloom event.
The bloom dissipated in the winter of 2018/2019. Red tides in Florida can last as little as a few weeks or longer than a year. They may even subside and then reoccur. In 2005, for example, a bloom started off the coast of St. Petersburg, Florida, in January and then spread from there to Pensacola and Naples by October, persisting for the majority of the year. The duration of a bloom in nearshore Florida waters depends on physical and biological conditions that influence its growth and persistence, including sunlight, nutrients, and salinity, as well as the speed and direction of wind and water currents. Researchers are watching oceanographic conditions in the region carefully and using forecasting tools similar to seasonal weather forecasts to predict how long this bloom will last.
Red tides occur less frequently and are less persistent in Texas than in Florida, but have increased in recent years. The mechanisms leading to blooms in the two regions are thought to be different, but more research is needed to understand possible connections.
Tropical storms may affect red tides by moving ocean water around. For example, a harmful algal bloom off the coast of southwest Florida in 2005 was carried up to the Florida Panhandle during Hurricane Katrina. Regarding the algal bloom currently affecting Florida, it appears to have intensified and spread to the Florida Panhandle after Tropical Storm Gordon in Sept. 2018 (however, researchers have not yet conducted a thorough analysis of the effects of this storm on the bloom). The Sept. 2018 algal bloom in Texas was likely a separate event, occurring at the time of year that is typical for such blooms in that region.
NOAA conducts scientific research and provides forecasts to give communities advance warnings to better deal with the adverse environmental impacts, health effects, and economic losses associated with red tide and other harmful algal bloom events.
NOAA monitors conditions year-round and provides official forecasts for red tide through two main products: conditions reports and bulletins. The conditions report identifies the risk of respiratory irritation in a county over the next three to four days. Bulletins provide decision-makers with a more in-depth analysis of the location of a current bloom and reported impacts, as well as forecasts of potential development, intensification, transport, and associated impacts of blooms. Both products are updated twice weekly during a bloom.
In addition, NOAA, along with its trained and authorized partners in the marine mammal stranding network, work together to respond to stranded marine animals found along the coastline.
The following are reports about NOAA National Centers for Coastal Ocean Science (NCCOS) activities related to this specific red tide event:
Stopping a bloom of this scale may not be possible. In the early 2000s, NOAA funded studies to test the use of clays to control red tides. Since that time, different types of clays have been developed in Asia that have fewer environmental effects. The State of Florida is now providing funding to test the use of these newer clays on a small scale during the current bloom, using lessons learned from the earlier NOAA-funded studies.
The Florida red tide organism, Karenia brevis, produces potent neurotoxins, called brevetoxins, that can affect the central nervous systems of many animals, causing them to die. That is why red tides are often associated with fish kills. Mortalities of other species, including manatees, dolphins, sea turtles, and birds also occur.
Wave action near beaches can break open K. brevis cells and release the toxins into the air, leading to respiratory irritation. For people with severe or chronic respiratory conditions, such as emphysema or asthma, red tide can cause serious illness. People with respiratory problems should avoid affected beaches during red tides.
Red tide toxins can also accumulate in filter-feeder mollusks such as oysters and clams, which can lead to Neurotoxic Shellfish Poisoning (NSP) in people who consume contaminated shellfish. While not fatal, NSP causes diarrhea and discomfort for about three days. Rigorous state monitoring of water and shellfish assures that commercial shellfish is safe, often by closing harvest beds. Recreational harvesters have the greatest risk of NSP, often due to a lack of awareness of the problem. Harvesters should check Florida or Texas websites to determine if it safe to harvest shellfish in areas of these states. To learn more about red tide health concerns in general, Florida and Texas offer online resources.
This year’s bloom is different from what we’ve seen before in several ways:
Timing: Blooms of this algae typically start in late summer or early fall. The current Florida bloom is similar to a bloom that lasted from 2004 to 2006 with the greatest impacts in 2005. That bloom spread to northwest and east counties, resulting in severe mortalities of many species, widespread closures of shellfish harvesting, and hypoxic bottom waters (especially in reef areas).
Duration: While not unprecedented in its duration, this bloom is unusually persistent. It started in October 2017 and continued through spring of 2018. By early summer, the bloom resurged and was detected in five southwest Florida counties. Some shellfish harvesting areas have been closed since November 2017. In September, following Tropical Storm Gordon, it spread to the Florida Panhandle. At the beginning of October 2018, it has been observed along the east coast of Florida.
Size: The size of the bloom changes from week to week, and it is patchy. Not every beach is affected every day, so it is important to stay up to date with the NOAA conditions report. As of August 15, the bloom stretched from Pinellas County to Collier County, more than 150 miles.
While the timing, duration, and size of this red tide are unusual, red tides are not new to the Gulf Coast. Red tides were documented in the southern Gulf of Mexico as far back as the 1700s and along Florida's Gulf coast in the 1840s. Fish kills near Tampa Bay were even mentioned in the records of Spanish explorers. For more information on historical red tide events in Florida, see the Florida Fish and Wildlife Conservation Commission's harmful algal bloom monitoring database.
If you see sick, injured, or stranded wildlife, such as a sea turtle, manatee, dolphin, seabird, or a large fish kill in Florida, report it to the following standing network hotlines. To report an injured, hooked, entangled, or stranded sea turtle, call 1-877-942-5343. To report other sick or injured wildlife and fish kills, contact FWC Wildlife Alert or call 888-404-FWCC (888-404-3922). If you see dead or injured marine mammals, call 1-877-WHALE HELP (1-877-942-5343). You can also report via the Dolphin and Whale 911 Phone App.
There is no way to project the cumulative effects of this red tide event. Red tide occurs naturally in coastal waters of the Gulf of Mexico with blooms appearing seasonally. Although the Florida red tide organism, Karenia brevis, typically blooms between August and December, blooms often deviate from that time frame. The current bloom continues to be monitored by our local and state partners. Visit the Florida Fish and Wildlife Conservation Commission's (FWC) red tide status page. Reports of fish kills and marine animal deaths are made publicly available on FWC’s website. For more information on the effects of red tide on marine animals, shellfish, and people, visit our health information page.
NOAA’s Red Tide Bulletins are issued twice weekly during a red tide event.
NOAA National Centers for Coastal Ocean Science projects, news, products, data, and general information related to harmful algal blooms.
Consolidated site from Florida Department of Environmental Protection for all Florida algal bloom resources.
Florida Department of Health red tide Information.
Red tide status, frequently asked questions, tools for tracking red tides, and general information from Florida Fish and Wildlife Conservation Commission.
Resources on aquatic toxins, to include Florida red tide, from Florida's Poison Control Center.
Mote Marine Laboratory’s beach conditions report and red tide information.
Frequently asked questions from Florida Sea Grant.