Karenia brevis (light micrograph)
Karenia brevis is a single-cell organism belonging to a group of algae called dinoflagellates. Karenia brevis is known as the Florida red tide organism. In large numbers, it causes red tide along Florida’s coastline. Karenia brevis can be found in Gulf waters any time of the year, but most commonly in the fall. Large concentrations of these cells, called blooms, can discolor water red to brown. Karenia brevis produces a neurotoxin that can kill fish and other marine life, make shellfish toxic for human consumption, and cause respiratory irritation in humans who breathe the aerosols released by the cells when they break open.