The influence of introduced European green crabs (Carcinus maenas) on habitat selection by juvenile native blue crabs (Portunus pelagicus)

Abstract

The European green crab (Carcinus maenas) is a highly successful marine invader, having established populations in a number of areas outside its natural range in the last 100 years. In South Australia,C. maenas can be abundant on intertidal mud flats, which are used by juveniles of the native blue swimmer crab (Portunus pelagicus) and could have the potential to cause substantial negative effects on this species. The influence of adult blue and green crabs on habitat selection by juvenile blue crabs was tested to determine if they responded to both predators in a similar fashion. The presence of predators did not influence habitat selection by juvenile blue crabs in either laboratory or field experiments, but juvenile behavior in the selected habitat did differ between the two adult species. Many more crabs buried themselves beneath the substrate when adult conspecifics were present than when adult green crabs were present. Burying in the presence of adult green crabs was no more frequent than when predators were absent. It remains to be determined if this makes juvenile blue crabs more vulnerable to predation by green crabs than by adults of their own species, or if the difference in response is because green crabs pose a different or lesser threat.