Clash of the crabs: Interspecific, inter-cohort competition between the native European green crab, Carcinus maenas and the exotic brush clawed crab Hemigrapsus takanoi on artificial oyster reefs

•The interaction between native Carinus maenas and the exotic Hemigrapus takanoi is investigated.•Both species occupy the same habitat when similar sizes, but occupation by C. maenas is seasonal.•C. maenas is lower in abundance in the size range of the majority of H. takanoi in the field.•Lab experiments suggest H. takanoi is a more aggressive competitor for food than C. maenas.•Competition between juvenile C. maenas and H. takanoi may lead to population changes.

Interaction between cohorts was investigated with juveniles of the native crab Carcinus maenas and adults of the exotic crab Hemigrapsus takanoi on artificial, intertidal oyster reefs. The reefs are occupied by C. maenas seasonally as a nursery habitat and consistently by adult H. takanoi. There was a distinct decrease in abundance of C. maenas of the same carapace width as most adult H. takanoi, suggesting competition at this size was occurring. Laboratory experiments indicated that H. takanoi was a more aggressive competitor for food and, with consistently high abundance on the reefs, may result in some exclusion of C. maenas from their nursery habitat. While total exclusion of C. maenas on the oyster reefs is unlikely, cohabitation may result in reduced population size or increased use of alternative nursery habitats.