THE INVASIVE ASIAN COPEPOD PSEUDODIAPTOMUS-INOPINUS IN OREGON, WASHINGTON, AND BRITISH-COLUMBIA ESTUARIES

At least six species of Asian copepods have been recently introduced t o the west coast of North America. Among them is Pseudodiaptomus inopi nus, which became established and abundant in the Columbia River estua ry between 1980 and 1990. Subsequently, the tidal regions of 18 smalle r rivers in the Pacific Northwest were sampled, using near-bottom pump s and vertical plankton net hauls. These samples indicate that II inop inus has not only invaded at least seven other estuaries in this regio n, 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 established P. inopinus populations was 19.3 degrees C, wh ereas those without P. inopinus had an average temperature of 12.4 deg rees C. Rivers with II inopinus had salinity intrusion zones of more t han 1 km length and those without P. inopinus usually had intrusion zo nes of less than 1 km.