Florida Harmful Algal Blooms

There are many different species of algae that cause Harmful Algal Blooms in Florida. Below are descriptions of some of the most hazardous and well-documented blooms. To view the status of Harmful Algal Blooms in Florida or to report a bloom visit the Florida Department of Environmental Protection.


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Microcystis aeruginosa

This cyanobacterium, or “Blue-green algae”, is a freshwater species that typically blooms during warm, rainy months. These blooms originate in Lake Okeechobee and enter the St. Lucie Estuary and the Caloosahatchee River during seasonal freshwater releases. These cyanobacterium produce toxins called microcystins. While consuming contaminated water is known to cause damage to the liver or digestive system, the effects of inhaling the toxin or its bioaccumulation in seafood are not well documented.

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Aureoumbra lagunensis

Known as “brown-tide”, this alga grows in marine environments and has been documented in the Northern Indian River Lagoon, Mosquito Lagoon and the Banana River. Since 2015, a vast and persistent Aureoumbra lagunensis bloom in this region has caused major ecological shifts as well as some of the largest fish kills on the east coast of Florida. This species has no known negative impacts on human health.

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Karenia brevis

Also known as “red-tide”, this dinoflagellate blooms annually in the Gulf of Mexico, usually during late summer or early fall, and widely impacts the west coast of Florida. Under rare circumstances, currents can transport these blooms south, and around the tip of Florida where they can then impact the east coast. Karenia brevis produces brevetoxin, a neurotoxin that can cause neurologic shellfish poisoning if consumed, or more commonly, asthma-like symptoms if inhaled.

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Pseudonitzchia sp.

This diatom occurs throughout coastal Florida, specifically the Indian River Lagoon, and generally blooms during the spring and fall. Even in high abundances, this species cannot be seen with the naked eye. It produces a toxin known as domoic acid, a neurotoxin that can cause amnesic shellfish poisoning if consumed. High doses of domoic acid can be fatal, but lower doses can still cause brain damage in the form of short-term memory loss. To date, no clinical cases have been documented in Florida.

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Pyrodinium bahamense

This dinoflagellate typically blooms in water bodies that have brackish salinities, shallow depths and low flushing rates. Annual blooms occur in Tampa bay and the northern Indian River Lagoon between April and October. Pyrodinium bahamense produces saxitoxin, a neurotoxin that, when consumed, can cause both paralytic shellfish poisoning and saxitoxin pufferfish poisoning.

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Synechococcus sp.

This cyanobacterium, or “blue-green algae” has only been known to bloom in Florida Bay. The most recent bloom started in late 2016 and subsided in early 2017. There have been no human health implications documented.

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Gambierdiscus toxicus

This dinoflagellate grows attached to macroalgae, dead coral and sand and occurs regularly during the summer months throughout the Florida Keys. Blooms are invisible to the naked eye but can produce ciguatoxin, a neurotoxin that accumulates in reef fish. When consumed by humans, the toxin can cause ciguatera which leads to nausea, rash and sometimes serious cardiac and neurological abnormalities. Ciguatoxin cannot be detected by appearance, taste or smell and is not removed by freezing or cooking the fish.

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While most HABs are formed by phytoplankton, some macroalgal species can cause economic and environmental issues when they bloom uncontrollably. One example is Sargassum, a seaweed that forms floating mats on the ocean’s surface. When this alga has an explosion of growth, these mats can block light from coral reefs and cause tourism declines when they wash up on beaches. Once the algae begins to decay, it can release hydrogen sulfide gas and make coastal areas unpleasant to recreate near. These blooms typically happen every summer in south Florida, although some years are worse than others.

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