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Karenia brevis

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Karenia brevis
Red tide at night panorama.jpg
Scientific Classification
Scientific Name

Karenia brevis

Red tide on rocks.jpg
Blooms on shore

Karenia brevis is a bioluminescent dinoflagellate that affects large portions of water in the Gulf of Mexico and the East coast of North America.[2] It is not a problem by itself and even has a few benefits for its ecosystem. The most important of these benefits is the oxygen it produces. The introduction of different chemicals, temperatures, and salt levels are what awakens this sleeping giant.

K. brevis is found year-round at concentrations of 1,000 cells per liter or less, which is far too little to notice. At levels as low as this there are no ill side affects from the cells being there whatsoever. The problems start when they form blooms, massive clumps of phytoplankton, that contain K. brevis almost exclusively by out-competing other phytoplankton species. These blooms are called red tides, or harmful algal blooms (HABs). There are over 50 HAB species in the Gulf of Mexico. K. brevis produces harmful toxins called brevetoxins. Brevetoxins are capable of killing fish, birds, marine animals and even cause major health problems in humans.[3]

They were formerly known as Gymnodinium breve.

Body Design

S.E.M. of K. brevis

K. brevis is shaped a like a square with rounded edges. Cell size ranges from about 18-45 µm in length and width, with a thickness of 10-15 µm (micrometers). Inside the cell there is a spherical nucleus in the left side of the hypocone. There are also yellow-green chloroplasts, giving the dinoflagellate its color. The flagellum located at the rear of the cell is usually as long as the cell itself. There is a large amount of variability in size, shape and width of the cell, and in the number of chloroplasts. [4] Each cell has two flagella that move it through the water at a speed of one meter per hour. ‘’K. brevis’’ thrives in high-salinity areas but can tolerate a wide range of salinities and temperatures.[3]

K. Brevis is photosynthetic and cannot survive below 200 feet underwater, as it needs direct sunlight to function. The cell can survive in temperatures between 4 and 33 degrees Celsius, and its optimal range is between 22-28 degrees Celsius. It can also survive in waters with salinities of 25-45 ppt (parts per thousand). It recovers energy by making use of organic molecules like nitrogen and phosphorus. It also consumes other photosynthetic prokaryotes to gain the energy needed to propagate. Groups of K. brevis turn into blooms because of chemical imbalances in the water caused by many different reasons, but usually this occurs because companies pour their chemicals into run-off zones. The problem chemicals like nitrogen come from fertilizers that are used nearby water access points. If levels of nitrogen pass normal levels, a red tide is imminent.[5]

Life Cycle

The blooms can cover massive areas as shown here

Karenia brevis reproduces asexually through binary division at a speed of 0.2-1.0 divisions each day depending on the solution the cell is in. The growth of it is limited by these factors: temperature, salinity, and available nutrients. They also reproduce sexually, although little is known about the process. We do know that the vegetative cells are haploid and that the gametes (sex cells) are [[isogamous. This means that these cells are effectively genderless as far as reproduction is concerned.[4]

Blooms develop in four stages; initiation, growth, maintenance, and termination. The initiation stage starts when a population of K. brevis accumulates and moves into one area. During growth, the population increases. Within a few weeks, K. brevis concentrations may be just high enough to kill fish. While in maintenance, wind and currents control the bloom’s movement. If it heads inshore, nutrients from land can incur bloom expansion. Stage four is termination, where wind and water currents break apart the bloom and reduce the concentration of cells.[3]


Blooms may become populated enough to turn the whole area milky red

K. brevis blooms appear in the Gulf of Mexico nearly annually, usually in late summer or early fall. Blooms can appear anywhere inside the Gulf of Mexico, and some even on the east coast of North America. Most blooms last around three to five months, covering hundreds of square miles, but can continue randomly for as long as 18 months. In Florida, red tides originate in nutrient-poor water 18 - 74 kilometers (11 to 46 miles) offshore. The brevetoxins affect the area around red tides in multiple ways. Wave action breaks open cells and the toxins becoming airborne.[3]

Masses of dead infected fish can also release a horrible odor containing the toxins, which are then inhaled. The decomposing masses of sea creatures depletes oxygen from the water, hurting the ecosystem heavily, not to mention the smell.[6] The air affected by K. brevis is not all bad however, as it produces large amounts of oxygen. Some estimates as to just how much they produce landed at 20%. Other ways K. brevis interacts with its environment include eating competing species of phytoplankton and providing food for larger organisms.[5]

Effects on Humans

Blooms of K. brevis devastate the economy of the affected area, especially coastal tourism centers. These areas lose millions of dollars when dead fish wash up on beaches and when tourists report eye and respiratory irritation. Shellfish-harvesting businesses lose massive amounts of money when they are forced to leave their usual shellfish beds alone. A study of three red tide blooms in the 1970s and 1980s showed losses from tourist and harvesting industries between $15 - $25 million.[3]

The fish affected by K. brevis die and wash up on beaches. People then get puncture wounds from stepping on the bones of these dead fish. Ingestion of neurotoxins from infected shellfish causes a debilitating, but non-fatal, neurotoxic shellfish poisoning (NSP) which is why harvesting companies cannot farm the shellfish while red tides are present. Breathing the airborne toxins results in severe respiratory irritation, stinging of the eyes, nose, and a dry cough. There are some incidents of contact irritation as well.[2]


A brief showcase of K. brevis and what it can do


  1. Karenia (Chromista) Wikispecies. Web. last edited April 8, 2017 Unknown, Author.
  2. 2.0 2.1 Magaña, Hugo.A historical assessment of Karenia brevis in the western Gulf of Mexico Science Direct. Web. Published April 14, 2003.
  3. 3.0 3.1 3.2 3.3 3.4 About Florida Red Tides FWC. Web. Accessed January 15, 2018. Unknown, Author.
  4. 4.0 4.1 Hargraves, PE.Karenia brevis Smithsonian Marine Station at Fort Pierce. Web. Last Updated October 3, 2011.
  5. 5.0 5.1 Karenia brevis Microbe Wiki. Web. last modified February 29, 2012 Unknown, Author.
  6. Pierce, R.Harmful algal toxins of the Florida red tide (Karenia brevis): natural chemical stressors in South Florida coastal ecosystems Nation Center for Biotechnology Information. Web. Published august 30, 2008.