Heterosigma akashiwo

General Flagellate
Shape Spheroidal or Close


Oval or egg-shaped.

or sometimes lumpy (cornflakes)
Size Diameter > 25 μm
Colour Greenish to golden-brown
Connection None (solitary)
Covering None


(plural: flagella) A tail-like projection that sticks out from the cell body and enables movement.

Two equal


An organelle in the cell that contains the cell pigments (Horner 2002). This is where photosynthesis occurs. A chloroplast is a specialized chromatophore.

Many Close



golden-brown chloroplasts peripherally
Lifestyle Close


The chemical process by which light energy, water and carbon dioxide are combined to produce oxygen and organic compounds. Photoautotrophic organisms (plants and algae) use this reaction to produce their own food.

. Asexual.


A rapid increase or accumulation of algal populations in an aquatic system. This will likely involve one or a few dominant phytoplankton species. This follows seasonal patterns (i.e., spring, summer or fall bloom) with dominant species being those that are best adapted to the environmental conditions of that time period. Discolouration of the water may be observed because of the algae's pigmentation. Blooms are often green but may be yellow-brown or red depending on the species present.

Extensive blooms mid-summer
Harmful effects Toxic, fish kills
Habitat Coastal including fjords and Close


The area where a river meets the ocean. Often characterized by high sediments, high nutrient levels, salinity fluctuations and tidal mixing.

Geographic Cold temperate to tropical waters worldwide
Seasonal Mid-summer
Growth Conditions


The dissolved ion content of a body of water. Can be measured in the following units: parts per thousand (PPT or ‰), practical salinity units (PSU), and absolute salinity (g/kg). PPT is measured by weight, denoting the number of parts salt per thousand total parts or a value of 10-3. PSU measures the conductivity of saltwater and compares it in a ratio to a standard KCl solution (because this is a ratio, salinity measured in this way can also be written without units). The newest unit of salinity is absolute salinity, which uses the mass fraction of salt in seawater (g salt per kg seawater) rather than its conductivity (TEOS-20 2010).

5 - 34
Temperature > 15 °C


Olisthodiscus carterae Hulburt
Entomosigma akashiwo Hada
Heterosigma akashiwo (Hada) Hada
Heterosigma carterae (Hulburt) F. J. R. Taylor
(Horner 2002)


Empire Eukaryota
Kingdom Chromista
Subkingdom Harosa
Infrakingdom Heterokonta
Phylum Ochrophyta
Subphylum Phaeista
Class Raphidophyceae
Order Chattonellales
Family Challonellaceae
Genus Heterosigma
Species H. akashiwo (Hada) Sournia

(Guiry and Guiry 2011)


Heterosigma akashiwo is a photosynthetic flagellate (Rensel 2007). H. akashiwo produce spherical Close


"A thick-walled dormant cell" (Horner 2002).

that are covered with mucilage (Montagnes 2006). These cysts are yellow-green to brown (Montagnes 2006). H. akashiwo cysts sink to the sea floor and can germinate the following year, producing another crop of swimming cells when conditions allow (Rensel et al. 2010).


Heterosigma akashiwo is a flattened, oval to pear-shaped, asymmetrical cell. Cells lack a rigid cell wall and can change shape rapidly. H. akashiwo is a Close


A member of the order Chloromonadida. Chloromonads are protists, have two flagella (one trailing, one extending forward) and have many disk-shaped chloroplasts (Encyclopedia Britannica 2011). Some species are principally responsible for farmed salmon kills since 1986. Large blooms have been observed along the BC coast (Taylor and Harrison 2002). Local example: Heterosigma akashiwo.

flagellate (i.e., it has two flagella, one trailing and one forward; Taylor and Haigh 1993). The two flagella are equal in length and each about same length as the cell. The Close


The front. The part of the cell in the direction of movement. Opposite of posterior (HPP 2003).

flagellum is used for swimming (Montagnes 2006). H. akashiwo cells swim rapidly and can rotate and change directions quickly (Rensel et al. 2010). H. akashiwo has 10 - 30 golden-brown chloroplasts and many mucocysts (Rensel et al. 2010). When preserved with chemical fixatives, the cell membrane shrinks tightly around the cell Close


A unit within the cell that serves a specific function and is usually enclosed by an individual lipid bilayer (membrane).

, giving the cell a lumpy look, similar to a blackberry.


Diameter: > 25 μm

Similar species


Harmful effects

H. akashiwo causes acute or chronic toxicity which leads to fish mortality. Fish have been observed to die when H. akashiwo concentrations exceed millions of cells per litre (Taylor and Haigh 1993). The exact cause of the fish mortalities is not yet clear. One common hypothesis suggests that H. akashiwo produces Close

Reactive oxygen species

Chemically reactive compounds that contain oxygen (i.e., oxygen ions or peroxides). They are natural byproducts of oxygen metabolism. Levels in the cell may increase with increased environmental stress (Apel and Hirt 2004).

reactive oxygen species
(ROS) such as hydrogen peroxide, which cause gill damage and respiratory failure (Rensel et al. 2010).


Coastal and inland seawater (fjords and estuaries) such as the Strait of Georgia (Rensel et al. 2010).


Found in west coast of North America especially near-shore and inland seawater from northern British Columbia to Mexico (Rensel et al. 2010).

Growth conditions

H. akashiwo is Close


Describing organisms that are able to withstand a wide range of salinities in the environment (e.g., fresh, brackish, salt).

and can grow at salinities as low as 5, though it grows significantly faster at salinities of 10 or higher (Rensel et al. 2010).

Environmental Ranges

Depth range (m): 0 - 100
Temperature range (°C): -1.948 - 12.224
Nitrate (μmol L-1): 1.278 - 7.035
Salinity: 5 - 34.704
Oxygen (mL L-1): 6.447 - 8.728
Phosphate (μmol L-1): 0.208 - 1.268

Silicic acid

A general term to describe chemical compounds containing silicon, oxygen and hydrogen with a general formula of [SiOx(OH)4-2x]n. Diatoms polymerize silicic acid into biogenic silica to form their frustules (Azam and Chisholm 1976).

(μmol L-1): 1.190 - 15.128
(EOL 2011)

Bloom characteristics

Extensive H. akashiwo blooms are observed in mid-summer following the initial spring diatom bloom. Blooms are aided by the vertical Close


The development of distinct non-mixing layers in the water column resulting from a steep gradient in density, which is caused by differences in temperature and/or salinity.

caused by the spring Close


A great rise or overflow of a river from heavy rains or spring thaw. In the Strait of Georgia, this usually occurs from March to June. (pers. comm. D. Cassis).

(the massive peak freshwater discharge by rivers; Rensel et al. 2010). Blooms in the Strait of Georgia coincide with the rise of water temperature to a minimum of 15 °C and decrease in salinity below 15. At Jericho pier in English Bay, Vancouver, this occurs in late May or early June, when freshwater runoff peaks and the Fraser River plume is largest. This stratifies the Close

Water column

Referring to a water system from the surface to the bottom sediments. This can be used to understand processes of stratification, mixing and their relationship to nutrient transport. Temperature, salinity, pH, and nutrient levels often vary along the length of the water column.

water column
in the Strait and supplies various Close


Various chemical substances that an organism needs for metabolism (i.e., to live and grow). These are usually taken up from the environment. Some examples include nitrate, phosphate, silica (for diatoms), iron, copper, etc. Some nutrients, like copper, are required for growth, but can also be toxic at high levels.

, such as iron (Taylor and Haigh 1993). H. akashiwo cell concentration in the Strait of Georgia can exceed 500 million cells L-1 of seawater during blooms (Taylor and Haigh 1993).


Encyclopedia of Life (EOL). Heterosigma akashiwo (Hada) sournia. http://www.eol.org/pages/911906. Accessed 02 July 2011.

Guiry, M. D. and Guiry, G. M. 2011. Heterosigma akashiwo (Hada) sournia. http://www.algaebase.org. Accessed 18 July 2011.

Horner, R. A. 2002. A Taxonomic Guide To Some Common Phytoplankton. Biopress Limited, Dorset Press, Dorchester, UK. 200.

Montagnes, D. 2006. Guide to Harmful Phytoplankton. University of Liverpool. UK. http://www.liv.ac.uk/hab/Data%20sheets/h_akas.htm. Accessed 16 Jan 2012.

Rensel, J. E. 2007. Fish kills from the harmful alga Heterosigma akashiwo in Puget Sound: Recent blooms and review. Rensel Associates Aquatic Sciences. Arlington, Washington, USA. 58.

Rensel, J. E., Haigh, N. and Tynan, T. J. 2010. Fraser river sockeye salmon marine survival decline and harmful blooms of Heterosigma akashiwo. Harmful Algae. 10(1): 98-115.

Taylor, F. J. R., Haigh, R. 1993. The Ecology of Fish-Killing Blooms of the Chloromonad Flagellate Heterosigma akashiwo in the Strait of Georgia and Adjacent Waters. In: Smayda, T. J. and Shimizu, Y. (eds.). Toxic Phytoplankton Blooms in the Sea. Elsevier, Amsterdam. 705-771

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