Smithsonian Marine Station at Fort Pierce

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Figure 1. Karenia brevis line drawing. Arrow indicates apical groove.

Figure 2. Karenia brevis living cell. Arrow indicates nucleus. Photo courtesy of Florida Fish & Wildlife Conservation Commission.

Figure 3. Karenia brevis. SEM image courtesy of Florida Fish & Wildlife Conservation Commission.

Species Name: Karenia brevis (Davis) Hansen et Moestrup
Common Name: Dinoflagellate
Synonymy: Gymnodinium breve Davis
Ptychodiscus brevis (Davis) Steidinger

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Protista Dinophyta Dinophyceae Gonyaulacales - Prorocentrum

    Use your mouse to rollover the terms in purple for their definitions. If this feature is not supported by your browser, please refer to the accompanying glossary for terminology.

    Species Description

    Cells of Karenia brevis are nearly square with rounded edges, and a somewhat prominent bulbous apical protrusion (Figures 1-3). They are considerably flattened dorso-ventrally, with a convex dorsal side and a concave ventral side (see video). The cingulum is slightly displaced, and the sulcus extends into the epicone (Figures 1 & 3). An apical groove extends from the sulcal extension across the apical protrusion and onto the dorsal side of the cell (Figures 1 & 3). Internally, the cell has a spherical nucleus in the left side of the hypocone, and a number of yellow-green chloroplasts (Figure 2). The trailing flagellum is usually at least as long as the cell (Figures 1 & 2, video). There is considerable morphological variability in size (see below), shape and width of the sulcal extension, and number of chloroplasts. The most conservative characters in Florida K. brevis cells are the shape and location of the nucleus and the apical groove length in relation to the epicone and sulcal extension (Steidinger et al. 1998). Haywood et al. (2004) provide a comparison in tabular form of K. brevis to similar species.


    Habitat & Regional Occurence

    The global distribution of Karenia brevis is uncertain, since cursory examination is insufficient to separate the 10 or more Karenia species now described. In the Gulf of Mexico, K. brevis is the dominant member of the genus, but it often co-occurs with K. mikimotoi (Miyaki et Kominami ex Oda) Hansen et Moestrup, and occasionally with K. papilionacea Haywood et Steidinger.  Karenia mikimotoi is distinguished from K. brevis primarily by lack of an apical protrusion and by its oval nucleus.

    Indian River Lagoon Distribution

    Karenia brevis is found in the IRL only rarely, probably because it is a neritic coastal species and does not proliferate in estuaries. It grows best in salinities of 25-40 PSU (Lekan & Tomas 2008 and references therein), though there is evidence of some strains adapting to lower salinity. Hydrodynamic incursion can transport K. brevis to Florida’s east coast at times (Anonymous 2008; Lenes et al. 2008; Walsh et al. 2009). A 2007-08 east coastal bloom brought K. brevis into the IRL (Phlips et al. 2011) at concentrations of >104 cells per liter, resulting in several shellfish closures (Wolny et al. 2008).



    Cell size ranges from about 18-45 µm in length, about the same range in width, and a thickness of 10-15 µm (Steidinger et al. 2008). Larger cells (70-90 µm) have been previously described (Steidinger et al. 1998; 2008) as K. brevis, but these are now ascribed to Karenia papilionacea Haywood et Steidinger (Haywood et al. 2004).


    Karenia brevis reproduces asexually by oblique binary division at a rate of 0.2-1.0 divisions per day (in culture). Growth rate is affected by salinity, temperature, and nutrient availability (Steidinger et al. 1998; Kusek et al. 1999; Lekan & Tomas 2008; Vargo 2009).


    The sexual cycle of K. brevis has been partly elucidated by Steidinger et al. (1998). Vegetative cells are haploid; gametes are isogamous with (+) and (–) mating types. Although not verified, the diploid planozygote with two longitudinal flagella presumably forms a hypnozygote.


    Florida “red tides” have their maximum development on the west coast of the state, but populations extend west across the Gulf of Mexico to Texas. Monitoring for presence and abundance of K. brevis is carried out continuously by the Florida Fish and Wildlife Conservation Commission ( There is considerable inter-annual variability in distribution and abundance, but most intense bloom development occurs during September to February. Populations often exceed 106 cells per liter. Causes of blooms and their intrusion into coastal areas are a major area of research (e.g. Steidinger 2009).

    Karenia brevis has attracted considerable attention because of its toxicity. It produces a group of lipophilic polyether compounds called brevetoxins (Quilliam 2003). These toxins can cause massive mortalities in marine vertebrates and human illness both from neurotoxic shellfish poisoning (NSP), and from respiratory irritation via aerosols (Anonymous 2008; Landsberg et al. 2009; Steidinger 2009). In addition to brevetoxins, other chemicals produced by this species may confer a competitive advantage to K. brevis via allelopathic effects over other phytoplankton (Prince et al. 2010). Environmental, economic, and public health costs of brevetoxins are considerable (Hoagland et al 2009; Landsberg et al. 2009). These multiple impacts have drawn interest in the molecular genetics of K. brevis (e.g. Haywood et al. 2004; Van Dolah et al. 2009) and Genbank ( contains over 300 sequences associated with the name Karenia brevis.


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    Anonymous. 2008. Illness associated with red tide – Nassau County, Florida, 2007. CDC Morbidity and Mortality Report 57(26): 717-720.

    Haywood, AJ, Steidinger, KA, Truby, EW, Bergquist, P, Adamson, J & L MacKenzie. 2004. Comparative morphology and molecular phylogenetic analysis of three new species of the genus Karenia (Dinophyceae) from New Zealand. J. Phycol. 40: 165-179.

    Hoagland, P, Jin. D, Polansky, LY, Kirkpatrick, B and 6 others. 2009. The costs of respiratory illnesses arising from Florida Gulf coast Karenia brevis blooms. Environ. Health Perspect. 117: 1239-1243.

    Kusek, KM, Vargo, G & K Steidinger. 1999. Gymnodinium breve – A scientific and journalistic analysis. Mar. Sci. Inst. Univ. Texas-Austin Contrib. Mar. Sci. 34: 1-229.

    Landsberg, JH, Flewelling, LJ & J Naar. 2009. Karenia brevis red tides, brevetoxins in the food web, and impacts on natural resources: Decadal advancements. Harmful Algae 8: 598-607.

    Lekan, DK & CR Tomas. 2008. Effects of varying salinity and N:P ratios on the growth and toxicity of Karenia brevis. 36-39 In: Moestrup, O. (Ed.). Proceedings of the 12th International Conference on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006. IOC-UNESCO, Copenhagen.

    Lenes, JM, Walsh, JJ, Weisberg, RH, Heil, CA and 4 others. 2008. A Karenia odyssey: model implications for current and future understanding. (abstract) ASLO Ocean Science Meeting, Orlando, FL, March 2-7, 2008.

    Phlips, EJ, Badylak, S, Christman, M, Wolny, J, Brame, J and 10 others. 2011. Scales of temporal and spatial variability in the distribution of harmful algae species in the Indian River Lagoon, Florida, USA. Harmful Algae 10: 277-290.

    Prince, EK, Poulson, KL, Myers, TL, Sieg, RD & J Kubanek. 2010. Characterization of allelopathic compounds from the red tide dinoflagellate Karenia brevis. Harmful Algae 10: 39-48.

    Quilliam, MA. 2003. Chemical methods for lipophilic shellfish toxins. 211-245. In: Hallegraeff, GM et al. (Eds.) Manual on Harmful Marine Microalgae. UNESCO Publishing, Paris.

    Steidinger, KA, Vargo, GA, Tester, PA & CR Tomas. 1998. Bloom dynamics and physiology of Gymnodinium breve with emphasis on the Gulf of Mexico. 133-153. In: Anderson, DM et al. (Eds.). Physiological Ecology of Harmful Algal Blooms. Springer Verlag, Berlin/Heidelberg.

    Steidinger, KA, Wolny, JL & AJ Haywood. 2008. Identification of Kareniaceae (Dinophyceae) in the Gulf of Mexico. Nova Hedwigia Beiheft 133: 269-284.

    Steidinger, KA. 2009. Historical perspective on Karenia brevis red tide. Harmful Algae 8: 549-561.

    Van Dolah, FM, Lidie, K, Monroe, EA, Bhattacharya, D and 3 others. 2009. The Florida red tide dinoflagellate Karenia brevis: New insights into cellular and molecular processes underlying bloom dynamics. Harmful Algae 8: 562-572.

    Vargo, GA. 2009. A brief summary of the physiology and ecology of Karenia brevis (Davis) Hansen and Moestrup red tides on the West Florida shelf and of hypotheses posed for their initiation, growth, maintenance, and termination. Harmful Algae 8: 573-584.

    Walsh, JJ, Weisberg, RH, Lenes, JM, Chen, FR and 11 others. 2009. Isotopic evidence for dead fish maintenance of Florida red tides, with implications for coastal fisheries over both source regions of the West Florida shelf and within downstream waters of the South Atlantic Bight. Prog. Oceanog. 80: 51-73.

    Wolny, JA, Scott, P, Brooks, C, Beadle, H, Brame, J and 4 others. 2008. Monitoring the 2007 Florida East coast Karenia brevis red tide and NSP outbreak. (poster) ICSR08 annual meeting.

Unless otherwise noted, all images and text by PE Hargraves
Editing and page maintenance by LH Sweat
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Page last updated: 03 October 2011


A longitudinal furrow, often partially enclosing the propulsive flagellum.


Groove located at the anterior part of many dinoflagellate species, extending porteriorly on both the ventral and dorsal surfaces of the cell; also known as the acrobase.


Back side of the cell, opposite of the front ventral side where the sulcus is located.


A furrow encircling the cell that contains the rotatary flagellum.


Front side of the cell where the sulcus is located, opposite of the back dorsal side.


The part of the cell below the cingulum; usually refers to a thecate (with cellulose plates) cell; may also be referred to as the hypotheca or hyposome.


The part of the cell above the cingulum; usually refers to a thecate (with cellulose plates) cell; may also be referred to as the epitheca or episome.

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