Pseudo-nitzschia australis
High resolution image of Pseudo-nitzschia australis. ©2001 Photo courtesy of Brian Bill, Northwest Fisheries Science Center.

Pseudo-nitzschia is another common diatom in Washington waters. The cells are long and slender and are joined into so-called stepped colonies by the overlapping of the cell ends. Some kinds of Pseudo-nitzschia produce a toxic compound called domoic acid. Shellfish (crabs, clams, mussels) that feed on phytoplankton containing high numbers of Pseudo-nitzschia can accumulate domoic acid and become dangerous for other marine life and humans to eat. Amnesic Shellfish Poisoning is the name given to the illness people get after eating shellfish containing domoic acid.