Potential Impacts of a Nonindigenous Crab on Selected West Coast Commercial Invertebrates

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Coastal Ecosystem and Public Health


Edwin Grosholz UNH - Department of Biological Sciences Principal Investigator
Dave Armstrong University of Washington School of Fisheries Co-Principal Investigator
Greg Jensen University of Washington School of Fisheries Co-Principal Investigator

The recent introduction of Carcinus to the west coast of the United States portends substantive ecological impact in estuarine and marine systems. We propose to study Carcinus" response to two categories of invertebrate prey, mobile Dungeness crab (Cancer Magister) and sessile bivalves, in order to gauge the potential ability of this exotic crab to significantly perturb populations of these valued commercial species by direct predation and displacement from habitat. Focus will be on epibenthic substrates (shell and gravel) characteristic of the Pacific northwest and frequently used as a refuge habitat to mitigate environmental impacts or improve commercial production, and which will likely be favored by Carcinus. The invasion of these habitats will be studied and resultant predator-prey dynamics as a function of density, tidal elevation and species mix will be quantified.


Experiments will be done in Bodega Bay, California. Shell colonization will be studied in situ with focus on seasonal and tidal interactions of Carcinus with two co-occurring species of crabs, Dungeness and Hemigrapsus.

Lab and field experiments with O+Dungeness crab will quantify both predation and emigration as behavioral responses affected by size and density; similar experiments using larger (1+) Cancer will be conducted to examine competitive interactions and assess potential for biotic control of Carcinus in subtidal channels.

Effects of substrate and prey size on the susceptibility of bivalves to Carcinus predation will be investigated using balanced, replicated lab experiments and both individual and mixed prey species.


Washington state has thousands of kilometers of coastal estuarine and inland water shoreline with numerous seasonally warm, protected bays that are both nurseries for major fisheries and sites for aquaculture of invertebrates worth tens of millions of dollars annually. These aquatic systems are also perfect habitat for proliferation of an ecologically robust, highly aggressive predatory crab that will soon have economic impacts as an exotic species in competition with, or predator of, these commercial species. Before it reaches Washington and British Columbia, it is wise to use the opportunity of initial presence in northern California to research interaction with species and use of habitats that typify much of the Pacific northwest. Results will provide guidance for growers, fishermen and managers as to the severity and nature of perturbations, and actions that might be taken to attenuate such inmpacts in numerous ways.