Chesapeake Bay Coastal Bays Rivers and Streams Watersheds
Maryland Department of Natural Resources

Heterosigma akashiwo

Heterosigma akashiwo was identified in Middle River of Chesapeake Bay during June 2002. Heterosigma is a bi-flagellated, single celled, golden brown alga in the family Raphidophyceae. In the United States it has been found on both coasts (Hargraves and Maranda 2002) and is considered the causative organism involved in fish farm kills in Washington State on the west coast. Net-penned fish deaths related to Heterosigma blooms have been particularly prominent in the northeast Pacific, notably around Japan.

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Predictability of blooms has been most related to temperature (warmer season waters >15 degrees C) and moderate salinity (approximately 15 ppt) in the coastal zone (Li and Smayda 2000, Connell and Jacobs 1997). Blooms have been observed to persist as long as stable water stratification persists in the warmer months. An unidentified ichtyotoxin (i.e., fish killing toxin) has been speculated as the causative agent in the net pen fish kills. There are no documented effects to humans from such blooms. No fish or human health effects have been associated with this species in Maryland waters.

Connell, L. and M. Jacobs 1997. Anatomy of a Bloom: Heterosigma akashiwo in Puget Sound 1997.

Hargraves and Maranda 2002. Potentially toxic or harmful microalgae from the northeast coast. Northeastern Naturalist. 9(1): 81-120.

Li, Y. and T.D. Smayda. 2000. Heterosigma akashiwo (Raphidophyceae): On prediction of the week of bloom initiation and maximum during the initial pulse of its bimodal bloom cycle in Narragansett Bay. Plankton Biol. Ecol. 47:80-84.

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