Heterosigma is a raphidophyte generally ~25um in diameter. The cell is slightly compressed and has two unequal flagella that it uses for movement. These cells contain many golden brown chloroplasts near the edges of the cell. Since their cell wall is not rigid, they can readily change shape. These fast swimmers can form extensive blooms in the mid-summer-fall when temperatures are above 15°C.
This genus is known to produce a naturally occurring toxin, which can cause fish kills, but the mechanism in which it can do so is unknown. It kills finfish, especially in net pens, as well as wild fish, and is known for antagonistic effects on organisms ranging from bacteria to fish.
Heterosigma has been identified in Washington since monitoring programs first began in 1960s, and the first recorded fish losses in the region were from a bloom near Lummi Island in 1976. These closures have had serious economic impacts on the communities dependent on these fisheries.
For more information about Heterosigma, please refer to NOAA’s Harmful Algal Blooms and Biotoxins page at: http://www.nwfsc.noaa.gov/hab/habs_toxins/hab_species/index.cfm
SoundToxins, a diverse partnership of Washington state shellfish and finfish growers, environmental learning centers, Native tribes, and Puget Sound volunteers, is a monitoring program designed to provide early warning of harmful algal blooms and Vibrio parahaemolyticus events in order to minimize both human health risks and economic losses to Puget Sound fisheries.