Can the native shore crabs (Carcinus maenas) become a barrier to the invasion of the round goby (Neogobius melanostomus) in Öresund, southern Baltic Sea?

Abstract: The round goby (Neogobius melanostomus) is a non-indigenous species to the Baltic Sea that has drawn the attention of many researchers in the last decade due to its rapid spreading and its impact on the local fauna. With recent concerns about the dispersal of the round goby towards the North Sea, the aim of this study was to determine if the native shore crab could compete with the invaders and prevent their advance. The ash-free weight and the handling time of four blue mussel size classes (7mm, 12mm, 17mm, 22mm) was measured for both predators in order to calculate their feeding efficiency on each size class. Selectivity experiments were conducted, in aquariums, to determine which size class was preferred by each predator. The results were in compliance with the optimal foraging theory; shore crabs consumed significantly more 17 and 22 mm mussels, while round gobies preferred significantly more 7 and 12 mm mussels. Competition experiments for a food source of ten mussels, with three treatments (goby vs. crab, goby vs. another goby, control), were also conducted. Round gobies were more dominant, consuming significantly more mussels than the crabs, indicating that the shore crab may not outcompete the invader in a limited prey situation.