The blue crab Callinectes sapidus Rathbun 1896 has become one of the most common invasive alien species (IAS) in the Mediterranean Sea. Thanks to its large environmental tolerance, high swimming capacity, and high fecundity, it is nowadays almost spread along the entire Mediterranean coastal area. In 2023, the occurrence of C. sapidus in the Mediterranean Sea reached the dimension of a massive invasion with direct impacts on the economy of artisanal small-scale fisheries. This species is a predator whose exponential expansion is raising concerns about the possible ecological consequences and the threats posed to native species. Indeed, invasive predators can have significant impacts on ecosystems by altering food webs and causing declines in native species populations. Here, we explored the chemosensitivity of C. sapidus in the detection and selection of prey in the field of predator-prey interactions.
In our experiments, we tested the food preferences of the blue crab by exposing it to different prey species: Mytilus galloprovincialis, Ruditapes decussatus and Cerastoderma glaucum. Male and female crabs were tested separately to identify possible feeding differences related to sex. The prey was presented to C. sapidus in four different manners: 1) alive, whole prey and 2) alive prey, but following removal of one valve, thus allowing the predator to use different sensory systems (smell, sight, touch) for food detection/selection, (3) agar-dissolved prey, so that the predator might only rely on the sense of smell and 4) prey shells filled with a different agar-dissolved prey (i.e. shells with smell of an alternative prey) to uncouple visual vs. olfactory inputs. Experiments lasted two hours and were videotaped for later analysis of the predator’s behaviour.
Results showed that, after tactile exploration, all prey was chosen by both males and females. Female crabs appeared more consistent than males in their choice, while males seemed more likely to make random prey selection, in agreement with the fact that their higher claw strength may allow them less selectivity in the choice. Therefore, the prey choice might be related to the size of the crab and especially to the strength of the claws. The same behavior of prey choice was observed when the prey supply was carried out in prey shell filled with agar-dissolved prey.
On the whole, our results suggest that the blue crab relies on both olfactory and visual inputs when making the choice.
This study provides valuable insights into the prey selection strategies of the blue crab C. sapidus, and how predators respond to different chemical cues emitted by various prey species. The study of the chemosensitivity of C. sapidus provides valuable insights into the mechanisms driving predator-prey interactions and ecosystem dynamics, with implications for conservation and management efforts. This approach is also useful for evaluating the effectiveness of baits to effectively attract blue crabs into traps and thereby counteract their expansion.