Feeding strategies of the invasive blue crab (Callinectes sapidus) on manila clam (Ruditapes philippinarum): Implications for aquaculture

The Manila clam (Ruditapes philippinarum) has become a key aquaculture resource in the Northern Adriatic lagoons. In recent years, the rapid spread of the invasive blue crab (Callinectes sapidus) has emerged as a major threat to clam farming. This study investigated blue crab feeding strategies on clam seed (15–30 mm), marketable clams (30–40 mm), and larger individuals (>40 mm) through two controlled laboratory experiments. The first experiment assessed feeding rates over a 24-h period, while the second analyzed handling behaviour using focal sampling and video recording. Results show that small clams were more frequently consumed, with males preying more actively than females. The 'Crushing' opening technique was predominantly used on smaller clams, while the more time-consuming 'Dactyl' opening technique was used for larger prey. These findings highlight the vulnerability of seed clams and underline the urgent need for management measures to mitigate predation by blue crabs in aquaculture settings.