SGER: Migration of a Hybrid Zone in Response to the 1997 El Nino Event

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Hilbish 9807055 The El Ni o/Southern Oscillation (ENSO) phenomenon is the most important process regulating year-to-year climate variation in the Pacific. The ENSO cycle affects patterns of ocean circulation as well as climate. During an El Ni o year there is an increased movement of water northward; consequently there is northward shift in the distribution of many marine species. The investigator, Dr. Thomas J. Hilbish of the University of South Carolina, has previously examined the distribution of a marine mussel that was introduced to Southern California earlier this century. Since its introduction this species has expanded its range northward and formed a hybrid zone with a native species of mussel. These mussels are important ecological constituents of marine communities on the west coast of North America and the introduced species is used in aquaculture operations in California and Washington. Previous studies indicate that the migration of the introduced species and the hybrid zone has stopped at Cape Mendocino, California. Dr. Hilbish will test the hypothesis that further migration northward has been prevented by upwelling that forms during the summer around Cape Mendocino, which causes the movement of mussel larvae offshore, where they die. Dr. Hilbish has predicted that migration northward would resume during an El Ni o year because upwelling is greatly reduced during this time. The 1997 El Ni o event is the second largest ever recorded and coincides with the period of time that mussel larvae are dispersed. Therefore he predicts that the northward movement of the introduced mussel species and the hybrid zone will occur this year and proposes to sample mussel juveniles as they recruit in the area around and north of Cape Mendocino. This work will test the hypothesis that circulation patterns controlled by the ENSO cycle regulate the dispersal and distribution of near-shore marine species, including marine mussels. This study will also help determine whether the expan sion of the introduced mussel species will continue and which regions are most likely to become contaminated. H:\POPBIO\ABSTRACT\HILBISH.txt