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

Biological invasions provide an opportunity to study one species in different contexts and allow us to investigate factors that control the distribution and abundance of species. Studying invaders in both the native and introduced ranges can inform us about invader traits, communities, and the interaction between an invader and the community that all determine whether an invader succeeds or fails. I used three different approaches to assess invasion success of an invasive invertebrate in a California estuary. First, I used long-term monitoring data, and small scale spatial experiments at a local level. Second, I conducted a short-term, broad scale biogeographic study, to assess an invader in both its native and introduced ranges. Third, I conducted laboratory experiments to assess inter- and intra specific aggression levels in an invader to assess whether there was a relationship between aggression and invasion success. In the local study, using long-term monitoring data I found that abundance of the European green crab, Carcinus maenas, in Elkhorn Slough estuary is temporally variable. High temporal variation is likely driven by recruitment limitation. I detected a negative relationship between abundance of green crab and species of small and large native crabs. These results suggest that control or eradication efforts would be most effective in years where recruitment, and adult abundance, is low, and that efforts should occur across all habitat types in the estuary.;The biogeographic study revealed that green crab abundance was an order of magnitude higher in the native range in Europe and on the US Atlantic Coast, than in the most recently invaded range, the US Pacific Coast. I found that proxies for invasion success, e.g. abundance, size, or ratio of invasive to native crabs, may lead to different conclusions of where the green crab is most successful. Finally, aggressive behavior was highly variable and I found a positive relationship between inter- and intraspecific aggression, which was not correlated to invasion success. Despite many examples of invaders that succeed in the introduced range, this species seem to face novel challenges rather than novel opportunity in the most recently introduced range, the US Pacific Coast.