Karenia brevis

Karenia brevis causes the red tide. The red tide is an algae bloom which takes on a red or brown color. Red tides are events in which estuarine, marine, or fresh water algae accumulate rapidly in the water column, resulting in coloration of the surface water. It is usually found in coastal areas. Karenia brevis is a microscopic marine algae that occurs naturally but normally in lower concentrations.

Neurotoxic shellfish poisoning (NSP) is caused by the consumption of shellfish contaminated by breve-toxins or brevetoxin analogs. Symptoms in humans include vomiting and nausea and a variety of neurological symptoms such as slurred speech. No fatalities have been reported but there are a number of cases which led to hospitalization. Marine animals can also consume the toxins released from the microscopic Dinoflagellates. 

The Gulf Coast economy is effected by NSP. It has been documented since at least the 1800s. When a red tide occurs, the harvesting and consumption of shellfish and crustaceans is banned until the event is over, and testing has confirmed that it is safe to eat shellfish again.