Elevated pCO₂ Affects Feeding Behavior and Acute Physiological Response of the Brown Crab Cancer pagurus

Anthropogenic climate change exposes marine organisms to CO₂ induced ocean acidification (OA). Marine animals may make physiological and behavioral adaptations to cope with OA. Elevated pCO₂ may affect metabolism, feeding, and energy partition of marine crabs, and thereby affect their predator-prey dynamics with mussels. Therefore, we examined the effects of simulated future elevated pCO₂ on feeding behavior and energy metabolism of the brown crab Cancer pagurus. Following 54 days of pre-acclimation to control CO₂ levels (360 μatm) at 11°C, crabs were exposed to consecutively increased oceanic CO₂ levels (2 weeks for 1200 and 2300 μatm, respectively) and subsequently returned to control CO₂ level (390 μatm) for 2 weeks in order to study their potential to acclimate elevated pCO₂ and recovery performance. Standard metabolic rate (SMR), specific dynamic action (SDA) and feeding behavior of the crabs were investigated during each experimental period. Compared to the initial control CO₂ conditions, the SMRs of CO₂ exposed crabs were not significantly increased, but increased significantly when the crabs were returned to normal CO₂ levels. Conversely, SDA was significantly reduced under high CO₂ and did not return to control levels during recovery. Under high CO₂, crabs fed on smaller sized mussels than under control CO₂; food consumption rates were reduced; foraging parameters such as searching time, time to break the prey, eating time, and handling time were all significantly longer than under control CO₂, and prey profitability was significantly lower than that under control conditions. Again, a two-week recovery period was not sufficient for feeding behavior to return to control values. PCA results revealed a positive relationship between feeding/SDA and pH, but negative relationships between the length of foraging periods and pH. In conclusion, elevated pCO₂ caused crab metabolic rate to increase at the expense of SDA. Elevated pCO₂ affected feeding performance negatively and prolonged foraging periods. These results are discussed in the context of how elevated pCO₂ may impair the competitiveness of brown crabs in benthic communities.