Population structure of Pseudo-nitzschia australis and its

Nicolaus G. Adams, Piper Schwenke and Vera L. Trainer
NOAA-Fisheries, Northwest Fisheries Science Center, Seattle, WA
Since 1991, contamination of razor clams with the neurotoxin domoic acid has resulted in
frequent closures of this important recreational and commercial fishery on the outer coast of
Washington State. However, prior to September 2003 domoic acid had not caused a closure of
shellfish harvesting in the inland waterways of Washington State. In September 2003 domoic
acid concentrations reached 29 ppm in blue mussels (Mytilus edulis) from Kilisut Harbor in
northern Puget Sound. Although this was the first closure due to domoic acid in the inland
waters of Washington State, diatoms of the genus Pseudo-nitzschia, which can produce domoic
acid, have been observed in Puget Sound waters since at least 1990. One of the species
responsible for the 2003 closure, as well as a subsequent closure in Puget Sound at Penn Cove in
2005, was Pseudo-nitzschia australis. This species is frequently observed on the outer coast of
Washington State as well as in Puget Sound, and was thought to be the causative organism in the
first documented domoic acid event on the outer coast of Washington in 1991. Microsatellite
markers were used to characterize two distinct populations of a different species, Pseudonitzschia pungens, on the Pacific coast of Washington State and British Columbia, but this
species produces low levels of domoic acid and has not been responsible for shellfish harvest
closures in Washington State waters. Microsatellites will be used in a fashion similar to the
work with P. pungens to determine the population structure of P. australis in Washington State
waters. Additionally, the population specific production of domoic acid in P. australis will be
assessed in laboratory culture experiments using highly sensitive antibody-based methods. The
ultimate goal of this work is to determine whether certain genetically distinct populations of P.
australis are predisposed to producing higher concentrations of domoic acid and to characterize
those environmental conditions that are conducive to elevated production of domoic acid. If
certain populations prove to be more toxic than others, specific molecular markers will be
developed to pinpoint highly toxic populations. This will allow the development of risk
assessments for toxic P. australis blooms and optimal focusing of monitoring efforts so that the
effects of domoic acid contamination to human health in Puget Sound waters can be mitigated.