Buhle, E.R. and J.L. Ruesink, 2003. Context-Dependent Impacts of Multiple Invasive Species an a Threatened Native Species in a West Coast Estuary, University of Washington.

Proceedings of the Third International Conference on Marine Bioinvasions, La Jolla, California, March 16-19, 2003, p. 14.

Despite recent efforts to develop consistent methods of quantifying the ecological impacts of invasive species, many challenges remain. One difficulty is that the impact of a given invader may depend on ecological context, so small-scale measurements may not be representative of impacts throughout the invader’s range. To address this issue, it may be useful to identify factors, such as habitat attributes or resident community composition, that drive variation in an invader’s density or per capita effect. We are investigating such factors in the impacts of two invasive oyster drills, Ceratostoma inornatum and Urosalpinx cinerea, and the introduced oyster, Crassostrea gigas, on the threatened native oyster, Ostreola conchaphila in Willapa Bay, Washington. High drill densities are associated with C. gigas reefs and aquaculture beds. In addition, observations of damage to drill shells and results from a tethering experiment indicate that predation by native cancrid crabs may significantly influence drill distribution and density. Drills preferentially select C. gigas when presented with both oyster species in feeding trials, suggesting that predation impacts on native oysters may depend on the relative abundance of alternative prey. An enclosure experiment designed to test direct and indirect interactions among C. inornatum and the two oyster species found that predation rates on O. conchaphila decrease with increasing abundance of C. gigas, though the effect is statistically nonsignificant. This effect was not detectable in field measurements of O. conchaphila mortality rates across community types. Our results to date suggest several mechanisms whereby physical habitat factors, native community composition, and interactions among invasive species could modify both the abundance and per capita impact of invaders. More work will be needed to quantify the relative importance of these mechanisms.

Contact: Eric Buhle, Department of Zoology, University of Washington, Box 351800, Seattle, WA 98195, USA
Key Words: Nonindigenous, Colonization, Population_dynamics
Product Type: Publication, Proceedings
User Type: Resource_Management