[1][2] It is a swimming marine alga that episodically forms toxic surface aggregations known as harmful algal bloom.

[5] Molecular techniques for identification (including quantitative PCR) are preferred over traditional microscope fixing, which may lyse the cells.

[5] Heterosigma akashiwo has been identified off the coasts of the United States, Canada, Chile, the Netherlands, Scotland, Ireland, Sweden, Norway, Japan, S.Korea, Hong Kong, Australia, New Zealand and South Africa.

[7] Heterosigma akashiwo is a mixotrophic alga, supplementing nutrient uptake and photosynthesis with ingestion of bacteria.

[7] A 2007 review of these blooms in Puget Sound suggested that salmon farming was probably not a strong driver of their incidence or severity.

[13] The exact mode of bloom toxicity is currently unknown, but gill damage leading to hypoxia is the proposed cause for fish death.

[5][7] H. akashiwo may produce brevetoxins, but others suggest the concentrations of these toxins are too low to account for such a large effect on fish populations.

[5] Heterosigma forms massive golden tides that impact the survival of organisms at every trophic level.

This alga has been shown to kill finfish, compromise fish and sea urchin egg development, and impact copepods, as well as oyster survival.