Edinburgh Napier University

  The impact of predators is often relative to the spatial scale at which the study is conducted. In this paper we investigated how spatial scale might influence the importance of predation. In doing this we addressed the hypothesis of scale-dependency in predation experiments. The predator studied was the shore crab, Carcinus maenas (L.), and its impact on intertidal macrofauna communities was assessed using a caging experiment. Two different treatments, small and large enclosure cages (of, respectively, 0.25 and 1 m2), were established in a completely randomised design on two different sites, mud and muddy sand, which differed physically but were very similar biologically. The density of crabs per square metre was 48, much larger than the ambient density but comparable with previously published work. The experiment ran for a month and the resulting data and summary statistics were analysed using univariate and multivariate methods. Results indicate that the impacts of crab predation were similar in the different cage sizes but different on the different sites. The present work demonstrates the importance of scale in interpreting the results of caging experiments, but not at the small-scale level of cage size.