''Alexandrium catenella'' is a species of

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s. It is among the group of ''Alexandrium'' species that produce toxins that cause paralytic shellfish poisoning, and is a cause of

red tide A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...

. ''Alexandrium catenella'' is observed in cold, coastal waters, generally at temperate latitudes. These organisms have been found in the west coast of North America, Japan, Australia, and parts of South Africa. ''Alexandrium catenella'' can occur in single cells (similar to '' A. fundyense''), but more often they are seen in short chains of 2, 4, or 8 cells. The organism is typically 20–25 μm in length and 25–32 μm in width. The cells are compressed both in the anterior and posterior ends of this specimen. ''Alexandrium'' has two

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

that enable it to swim. While one flagellum encircles the cell causing the cell the rotate and move forward, the other extends behind the cell and controls the direction. In some instances, these organisms can appear like small trains moving in the water under a microscope. ''Alexandrium catenella'' spends the majority of its life in a resting cyst state, in which it cycles between dormancy and quiescence in benthic accumulations called cyst beds, which can act as seed banks for future blooms. Resting cysts are colorless and ellipsoid in shape, ranging between 38 and 56 um long, and 23-32 um wide, and are difficult to distinguish from the cysts of '' Alexandrium tamarense''. The resting cysts germinate once environmental conditions, mainly sustained warmer temperatures, are favorable, and will produce motile cells capable of

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

and

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...

, which form the blooms associated with

paralytic shellfish poisoning Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfi ...

(PSP). The dinoflagellate produces

saxitoxin Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin. Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralytic she ...

, which is a highly potent

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

. If consumed, this toxin can cause

(PSP). By ingesting saxitoxin, humans can suffer from numbness,

ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...

, incoherence, and in extreme cases respiratory paralysis and death. The toxin was discovered in 1927 in central

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. Shellfish poisoning affected over a hundred humans, and now saxitoxin is recognized as one of the most deadly algal toxins. These algal blooms have caused severe disruptions in the fisheries of these waters, and have caused filter-feeding shellfish in affected waters to become poisonous for human consumption. Because of this, A. ''catenella'' is categorized as a

harmful algal bloom A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...

(HAB) species. While in some areas the causes of HABs appears to be completely natural, in others, they appear to be a result of human activity, which is often coastal water pollution and over-fertilization. ''Alexandrium catenellas multiplication is stimulated by higher ammonia and inorganic nitrogen concentrations. The optimal growth conditions for ''A. catenella'' include a cool temperature of around 17 to 23 °C, a medium to light illumination of 3500 to 4000 lux, and a high salinity of around 26 to 32 percent.

See also

References

Further reading