Biogeographic investigation of variation in abundance, habitat use, and behavior of the European green crab, Carcinus maenas

Background/Question/Methods
Many studies of species invasions seek to quantify the degree to which a given area is invaded by a suite of different invaders. In contrast, the focus of this study is to quantify variation in invasion of a single invasive species, the European green crab, Carcinus maenas, at a biogeographic scale. Comparing invasions requires the ability to quantify and understand the mechanisms that lead to invasion success. The objective of this study is to measure parameters describing invasive green crab populations and to characterize variation in these indicators across a broad geographic range.

I sampled the native range of C. maenas, the European Atlantic coast, as well as the US Atlantic Coast invaded approximately 200 years ago, and the US Pacific Coast invaded approximately 20 years ago. All coasts were sampled in 2006 and 2007. On each coast, I measured individual traits (e.g. average and maximum carapace width, intra- and interspecific aggression) in addition to population traits (e.g. relative abundance, size distribution and habitat use (open coast vs. estuaries)), and the ratio of native to invasive crabs.

Results/Conclusions
My preliminary results include three key findings: 1) With respect to individual traits of average and maximum carapace width, C. maenas is significantly larger on the US Pacific Coast than on the US and European Atlantic Coast. 2) With respect to intra- and interspecific aggression, C. maenas on the US Atlantic Coast is less aggressive than C. maenas in their native range or on the recently invaded US Pacific Coast. This contrasts with my findings on carapace widths that found greater similarity between the two Atlantic coasts. 3) With respect to relative abundances and habitat use, C. maenas on the US Atlantic Coast is more similar to C. maenas in the native range, than is C. maenas on the US Pacific coast. Potential mechanisms leading to the absence of C. maenas on the US Pacific coast, in open coastal habitat are currently being investigated.

In order for community ecologists and coastal managers to better prioritize efforts of prevention, management, or eradication of invasive species there is a strong need for research addressing large scale biogeographic patterns of spatial variation in abundance, habitat use, and behavior of invasive species.