Karenia brevis

Karenia brevis is a microscopic, single-celled, photosynthetic organism that is part of the Karenia (dinoflagellate) genus, a marine dinoflagellate commonly found in the waters of the Gulf of Mexico. It is the organism responsible for the 'Florida Red Tides' (coastal infestations), commonly referred to as red tides that affect the Gulf coasts of Florida and Texas in the U.S., and nearby coasts of Mexico. K. brevis has been known to travel great lengths around the Florida peninsula and as far north as the Carolinas. Each cell has two flagella that allow it to move through the water in a spinning motion. K. brevis is unarmored, and does not contain peridinin. Cells are between 20 and 40 μm in diameter. K. brevis naturally produces a suite of potent neurotoxins collectively called brevetoxins, which cause gastrointestinal and neurological problems in other organisms and are responsible for large die-offs of marine organisms and seabirds. Karenia brevis was named for Dr. Karen A. Steidinger in 2001, and was previously known as Gymnodinium breve and Ptychodiscus brevis. The classification of K. brevis has changed over time as advances in technology are made. It was first named Gymnodinium brevis in 1948, but was later changed to Gymnodinium breve, which correlates with the guidelines of the International Code of Botanical Nomenclature. In 1979 it was categorized under the genus Ptychodiscus and named Ptychodiscus brevis as new research showed it fit better under this genus because of its morphology, biochemistry, and ultrastructure. Then in 1989, scientists agreed this organism should be referred to as its original name (G. breve). It was then reclassified and transferred to the new genus Karenia, which was established at the University of Copenhagen in 2000. K. brevis was first identified in Florida in 1947, but anecdotal reports in the Gulf of Mexico date back to the 1530s. Outbreaks of K. brevis have been known to occur since the Spanish explorers of the 15th and 16th centuries, as documented by Spanish explorers like Cabza de Vaca. These explorers noted large fish kills that resemble the die offs seen in present day due to K. brevis. C.C. Davis confirmed these die offs were due to K. brevis in 1948. K. brevis has an optimum temperature range of 22–28 °C (72–82 °F), an optimum salinity range of 25-45 Practical Salinity Units (PSU), has adapted to “low-irradiance environments,' and can utilize both organic and inorganic nitrogen and phosphorus compounds to survive. In its normal environment, K. brevis will move in the direction of greater light and against the direction of gravity, which will tend to keep the organism at the surface of whatever body of water it is suspended within. The swimming speed of K. brevis is about one metre per hour and the organism can be found throughout the year in the waters of the Gulf of Mexico at concentrations of ≤ 1,000 cell per liter. Scientists have been unable to determine a definitive geographic range for K. brevis specifically because it is difficult to separate from the ten other species of Karenia, but K. brevis is the most common species occurring in the Gulf of Mexico. K. brevis is the causative agent of red tide, which occurs when the organism multiplies to higher than normal concentrations. During these events the water can take on a reddish or pinkish coloration, giving these explosions in the K. brevis population the name of Florida Red Tide. These algal blooms caused by K. brevis produce brevetoxins, which can result in significant ecological impacts through the death of large numbers of marine animals and birds, to include marine mammals. Large scale fish kills are known to occur due to these Florida Red Tides caused by K. brevis. Fish species through the food chain are impacted, up to and including large predatory species such as sharks, as well as species typical in human consumption. Gabriel Vargo of the University of South Florida states that, “There is no single hypothesis that can account for blooms of  K. brevis  along the west coast of Florida'. However, like most algae, their occurrence and survival depends on a variety of factors in their environment including water temperature, salinity, light, and nutrients/compounds present in the water.