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Image of Alexandrium by Brian Bill, NOAA Image of Alexandrium by Brian Bill, NOAA

Image of Alexandrium by Brian Bill, NOAA

Photo credit: Brian Bill, NOAA

Phytoplankton of the month — May 2015

Alexandrium catenella

Alexandrium catenella is an armored dinoflagellate, approximately 24-24µm long and 22-44µm wide. Their round cells are identified by the shape and position of their pores and are often found in chains although solitary cells can also be observed.

This species is known to produce paralytic shellfish toxins (PSTs), which cause paralytic shellfish poisoning. Paralytic shellfish poisoning effects the neurological system and can result in tingling of the lips and tongue, loss of control of arms and legs, and respiratory arrest in humans if toxin levels are high. The accumulation of PSTs in shellfish is not a new phenomenon, nor is it one confined to Washington State. It has been occurring for hundreds of years in many parts of the world, primarily in temperate waters. Along the Pacific Coast, poisonous shellfish have been found all the way from Alaska to California. A member of Captain Vancouver's crew died in 1793 after eating toxic shellfish from an inlet in British Columbia, Canada, a place now known as Poison Cove. This was the first recorded PSP death in the Pacific Northwest. Native Americans were undoubtedly aware of the problem long before that, however. Washington State began intermittent testing for PSP in the 1930's with a more robust program beginning in 1957 after five Washington State residents suffered from PSP, three of whom died.

Alexandrium catenella can form resting cysts, when conditions are unfavorable, which allows for them to sit dormant for a period of time, re-emerging when environmental conditions are conducive to growth. The cysts are toxic and shellfish consuming these cysts can become toxic event when live cells of Alexandrium are not present in the water column. More information on Alexandrium cyst mapping in Puget Sound

The Washington Department of Health actively monitors and routinely closes shellfish harvesting areas when toxin levels are at or above 80 µg/100 g of shellfish tissue. SoundToxins volunteers identify and count Alexandrium catenella cells and provide an alert to the Department of Health when cells are observed.

The genus Alexandrium includes approximately 30 species, including A. catenella and A. tamarense. A. tamarense has been observed in northern Puget Sound.

For more information about PSP and to learn how to harvest shellfish safely, please refer to the Washington Sea Grant document Gathering Safe Shellfish.

For more information on Alexandrium see
Gathering Safe Shellfish
A Taxonomic Guide to Some Common Marine Phytoplankton, by Rita Horner (Biopress Ltd. 2002)

SoundToxins, a diverse partnership of Washington state shellfish and finfish growers, environmental learning centers, Native American tribes, and Puget Sound volunteers, is a monitoring program designed to provide early warning of harmful algal bloom events in order to minimize both human health risks and economic losses to Puget Sound fisheries.

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