The invasive Asian copepodPseudodiaptomus inopinus in Oregon,Washington, and British Columbia estuaries

At least six species of Asian copepods have been recently introduced to the west coast of North America. Among them isPseudodiaptomus inopinus, which became established and abundant in the Columbia River estuary between 1980 and 1990. Subsequently, the tidal regions of 18 smaller rivers in the Pacific Northwest were sampled using near-bottom pumps and vertical plankton net hauls. These samples indicate thatP. inopinus has not only invaded at least seven other estuaries in this region, but that it is sometimes the dominant zooplankter in these systems.P. inopinus occurred in estuaries of both large and small rivers and in rivers with and without international shipping. Two factors may be important in the establishment of this copepod: temperature and extent of salinity intrusion. In our samples, average autumn temperature of rivers with establishedP. inopinus populations was 19.3°C, whereas those withoutP. inopinus had an average temperature of 12.4°C. Rivers withP. inopinus had salinity intrusion zones of more than 1 km length and those withoutP. inopinus usually had intrusion zones of less than 1 km.