Karenia brevis is a marine dinoflagellate

Dinoflagellate

The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

 common in Gulf of Mexico waters, and is the organism responsible for Florida red tide

Red tide

Red tide is a common name for a phenomenon also known as an algal bloom , an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. It is usually found in coastal areas...

, as well as red tide in Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

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K. brevis is a microscopic, single-celled, photosynthetic organism that can "bloom" (see algal bloom

Algal bloom

An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...

) frequently along Florida coastal waters. Each cell has two flagella that allow it to move through the water in a spinning motion. K. brevis naturally produces a suite of potent neurotoxins collectively called brevetoxin

Brevetoxin

Brevetoxin , or brevetoxins, are a suite of cyclic polyether compounds produced naturally by a species of dinoflagellate known as Karenia brevis...

s, which cause gastrointestinal and neurological problems in other organisms and are responsible for large die-offs of marine organisms and seabirds.