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

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.Can shore crabs prevent a round goby invasion in the North Sea? 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. Several experiments were conducted in order to test the hypothesis. The average energy content for four blue mussel size classes (7mm, 12mm, 17mm, 22mm) was measured. The average handling time, for those size classes, for both predator species (shore crabs & round gobies) was also measured and was used to determine the prey value; how profitable it would be to consume a certain size mussel. A 12 hour selectivity experiment was conducted to test if the predators preferred their optimal prey size, when offered all sizes in equal numbers. Finally, a competition experiment with a limited food source (blue mussels) was performed with three treatments: a) goby-crab, b) goby-goby, c) control. The round goby proved to be a more efficient predator on average and dominated the limited food source in the competition experiments. Round gobies were significantly more efficient at consuming smaller mussels (15mm), while the round gobies showed a clear preference for smaller mussels (