predicting Alexandrium blooms

Understanding Dormancy Requirements and Germination of Alexandrium Cysts and Evaluating Cyst Mapping as a Tool for Early Warning of Harmful Algal Blooms

Studies revealed that surface-sediment cyst mapping alone may not reveal the full risk of Alexandrium catenella blooms. Determining the share of cysts capable of germinating helps shellfish growers anticipate toxic blooms.

Principal Investigator

Cheryl Greengrove, University of Washington, Tacoma

Co-Principal Investigators

Brian Bill, NOAA, NMFS, Northwest

Julie Masura, University of Washington, Tacoma

Stephanie Moore, NOAA, Northwest Fisheries Science Center


Washington Sea Grant-supported research tested the assumption that large-scale cyst mapping in winter can fully reveal summer bloom risk. They collected cysts from 100 sites throughout Puget Sound, incubated them to determine germination rates, and used microphotography and image analysis to see if “full” cysts were more likely to germinate. They also conducted experiments to determine the dormancy requirements of cysts and the seasonal regulation of germination. A bloom map was disseminated to the shellfish industry early in the growing season.

Research Updates


The alga Alexandrium catenella produces toxins that can accumulate in shellfish and cause death if ingested by humans. Limited ability to predict A. catenella blooms makes them a significant threat to public health and to Washington’s shellfish industry, which has been estimated to worth more than $100 million annually. Researchers have tried to predict summer blooms by mapping winter cysts in surface sediments. But this approach relies on the assumption that all cysts are capable of germinating; however, the share of cysts in “seedbeds” that actually germinate was unknown.


Only 16 to 66 percent of cysts from the 100 sampled stations germinated. Such wide variation suggests that traditional cyst mapping without a viability assessment does not accurately reflect the likelihood of dangerous blooms. By mapping the abundance of viable cysts throughout Puget Sound, this project has produced a more accurate indicator of the potential for toxic blooms. Researchers’ outreach helped shellfish producers become aware of areas at high risk of blooms.


Greengrove CL, Masura JE, Moore SK, Bill BD, Hay LR, Banas NS, Salathe EP Jr, Mantua NJ, Anderson DM, Trainer VL, Stein JE (2012) Alexandrium catenella cyst distribution and germination in Puget Sound, WA. In Kim, HG (ed), Proceedings of the 15th International Conference on Harmful Algae, Changwon, Korea, Oct. 29-Nov. 2, 4 pp.