An Invasive Crab Species Exhibits Greater Daily Behaviour Plasticity Than a Naïve Native Crab Species

Behavioural plasticity is considered highly relevant for biological invasions. As daily behavioural rhythmicity is plastic in response to environmental factors, we suggest that it may also be worth considering in the context of invasion success. We explored, under laboratory conditions, the potential role of plasticity in the recent invasion of the Atlantic blue crab ( Callinectes sapidus , Rathbun, 1896) in the Mediterranean Sea, by studying its behavioural rhythmicity in the presence of the native Mediterranean green crab ( Carcinus aestuarii, Nardo, 1847). Daily activity recordings under standardised photoperiod conditions (12‐h light:12‐h dark) revealed that both species exhibit daily behavioural rhythmicity with a nocturnal activity pattern. Notably, when in the presence of an individual from the other species, the Atlantic blue crab rapidly shifted to a pronounced diurnal activity pattern. The Mediterranean green crab's behavioural rhythm was also affected by the presence of the Atlantic blue crab, though to a much lesser extent. This suggests greater plasticity and contextual modulation in the daily behavioural rhythm of the Atlantic blue crab in response to the presence of other species, at least in the studied populations. Furthermore, across all conditions, the invasive species in our system was consistently more active than the native species. Plasticity in behavioural rhythms may differ between invasive and native species, and future studies should investigate whether and how these differences influence their interactions.