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Red Tide Events in the Gulf of Mexico

By: Alyssa Starmer

By: Flickr User AJC1

Algae is a vital source of oxygen and the basis of the food web in our oceans. Despite its vital contributions, certain species of algae have the potential to produce toxins that are harmful to both humans and marine systems. Harmful algal blooms (HABs), also known as red tide, occur when toxic algae, commonly species like Karenia brevis, are present in higher-than-normal concentrations. The algae produce brevetoxins, a type of neurotoxin that can cause many harmful consequences, particularly when inhaled or consumed.

Red tide events are frequent in southwest Florida regions along the Gulf Coast. These events typically occur annually during late summer and early fall and often last for around 3 to 5 months. In some cases, they can persist for as long as 18 months. The frequency of extreme red tide events has increased in the last 15 years, due to impacts of climate change including changes in temperature, salinity, rainfall patterns, coastal upwelling, and sea level rise. Human activities such as farming, sewage treatment, and factories have also impacted the frequency of red tides by increasing chemical runoff that can cause algae to grow faster.

Red tides form miles offshore where they are too far out to cause harm to humans but can still have adverse effects on the marine ecosystem. The problem arises for humans when onshore wind currents carry the red tide close to the coast. Natural factors such as tropical storms and hurricanes impact the location and intensity of red tides, causing the tides to be carried and spread further than typical currents may have taken them. The major factors contributing to the occurrence of red tides are warm ocean temperatures, low ocean salinity, high nutrient content, and rain followed by periods of sunlight.

Research at the University of Florida has shown that human activity has played a key role in intensifying red tides in the past decade. More specifically their research has shown that nitrogen inputs from coastal and inland sources intensified blooms in Charlotte Harbor. Since Increased nitrogen inputs can cause red tide events to last longer, it is important to focus efforts on finding ways to reduce the nitrogen load we as humans put into the ocean

The extent of red tide events depends on the movement and concentration of the algae. Higher concentrations and increased movement of these microorganisms could lead to larger consequences within the marine environment and on people. The brevetoxins produced in red tides affect the nervous systems of organisms and may lead to the mortality of fish, turtles, birds, and marine mammals. Extreme red tides can also lead to habitat loss and long recovery rates for fish populations. Marine populations will undergo more harm as the frequency of red tides increases and the recovery time between events shortens.

Red tide events can also have many consequences on human health, especially by consuming seafood affected by brevetoxins. Since shellfish are filter feeders, they are particularly vulnerable to red tides. As shellfish filter feed in areas affected by red tides, they consume brevetoxins which then accumulate within their tissues. When consuming toxic shellfish, people can fall ill with neurotoxic shellfish poisoning (NSP). Brevetoxins also become airborne at the surface and may impact human health by causing eye irritation and respiratory illness. In some cases swimming in less serious events is still okay, however, in extreme red tides swimming may cause skin irritation and burning eyes. These events can also impact fishermen socio-economically by affecting fish populations. Socio-economic impacts as a result of red tides are unpredictable because they are not uniform across the industry, depending on their business, adaptability, and duration of the red tide events. Red tides can also negatively affect the tourism industry mostly because fewer people visit Florida beaches during these events. One single red tide event can cost local Florida coastal communities millions of dollars.

During red tides, it is typically okay to consume shellfish from restaurants or seafood markets. Commercially available shellfish are often not local, if they are local to an area where red tide events occur, they are tested for brevetoxins before consumption. In any case, it is always best to check with the seafood supplier to ensure the shellfish is safe to consume. In addition, it is also typically okay to consume fish, crabs, shrimp, and scallops because the toxins are not normally absorbed in the edible tissues of those animals. One should never consume recreationally harvested shellfish from red tide areas, recreational harvesting is banned during red tide closures due to health risks. Additionally, cooking or freezing shellfish doesn't kill red tide toxins.

Satellite imagery monitors can track algae blooms at large spatial scales, helping to observe, identify, and alert local communities of offshore red tides before they reach the coast. Various monitoring instruments are also deployed to test for red tide algae in coastal waters. Scientists are working on discovering an antidote to red tide toxins. The advancement of technology increases our knowledge of red tides, and as a result, allows us to be better prepared for the impact of these events.

While red tide events often occur at large temporal and spatial scales, we can still take many measures to reduce the negative human and natural impacts of these events. At a local level, monitoring shellfish for toxins and closing shellfish harvesting during red tide events can reduce the likelihood of developing neurotoxic shellfish poisoning. People with respiratory problems are advised to avoid red tide areas, especially when winds are strong, or if dead fish are present as it may indicate the presence of the toxin. Individuals can help by reporting things like respiratory irritation, dead fish, or discolored water to local wildlife responders. Reporting distressed sea turtles, manatees, or dolphins is also beneficial, and individuals can ask their local county and city governments about local resources as well. Red tide beach conditions in Florida can be found using Mote’s Beach Conditions Reporting System. Red tides have become more frequent and intense in the Gulf of Mexico. By using the power of community, scientific, and technological developments to combat the ecological, societal, and health consequences of these events.

Works Cited

About Red Tides in Florida. Florida Fish And Wildlife Conservation Commission. (n.d.).,affecting%20thousands%20of%20square%20miles.

Blake, S. D., McPherson, M., Karnauskas, M., Sagarese, S. R., Rios, A., Stoltz, A. D., Mastitski, A., & Jepson, M. (2022). Use of fishermen’s local ecological knowledge to understand historic red tide severity patterns. Marine Policy, 145, 105253.

Bruckner, M. (2019, April 20). Red Tide. Red Tide.

Florida Red Tide. (n.d.).

Florida, U. of. (2022). Human activity “helped fuel” red tide events in Southwest Florida, new study reveals.

Staugler, B. (2018, August 9). Understanding Florida’s Red Tide. Florida Sea Grant.

US Department of Commerce, National Oceanic and Atmospheric Administration. (2018). Florida: Harmful Algal Blooms.

US Department of Commerce, National Oceanic and Atmospheric Administration. (2018). Gulf of Mexico: Harmful Algal Blooms.


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