Prey size and species preferences in the invasive blue crab, Callinectes sapidus: Potential effects in marine and freshwater ecosystems

The blue crab, Callinectes sapidus is an invasive species in the Mediterranean region. In Ebro Delta bays, it poses an important risk for the cultivation of Mediterranean mussel (Mytillus galloprovincialis) and Pacific oyster (Crassostrea gigas). Besides, the species thrives in the Ebro River hosting abundant populations of apple snail (Pomacea maculata) and Asian clam (Corbicula fluminea). Food-preference experiments were conducted to assess the effect of predator and prey sizes and prey type (M. galloprovincialis vs. C. gigas and P. maculata vs. C. fluminea) in predation patterns and its possible causes. Our results show that except for the Pacific oyster, which attains protection at sizes of 50–70 mm and was little consumed (0–16%), the other preys are readily predated, at variable rates (mussels: 38–96%; apple snail: 58–93%, and Asian clam: 67–100%), depending on predator and prey sizes. Juveniles and young blue crab adults showed greater consumption of small and medium mussels and a similar trend occurred with Asian clam. In contrast, large and medium apple snails were more heavily predated by adult blue crabs. Species comparisons also showed higher predation of mussels than oysters (71 vs. 8%), and of apple snail than Asian clam (99 vs. 72%). Once the shell barrier was removed, preference for mussels was still preserved, suggesting a nutritional preference. Our results point the need of fishing blue crab in marine areas to prevent losses in mussel production and highlight the potential control exerted over undesired invasive mollusk species.