Effects of laboratory holding time and diet type on labile traits in the crab Cancer irroratus Say, 1817 (Decapoda: Brachyura: Cancridae)

Abstract

Abstract Collecting animals from the field and bringing them into the laboratory elicits acute and chronic stress responses that may affect the interpretation of experimental outcomes. The effects of prolonged laboratory holding (three months) on labile traits (metabolic rate and spontaneous activity) were quantified for the Atlantic rock crab Cancer irroratusSay, 1817. The effects of diet (heterogenous versus homogenous) on crab condition (hemolymph protein density, crab mass, and chelal compression strength) were also assessed. When offered a heterogeneous diet C. irroratus displayed a clear preference for mussels and an aversion to herring and algae. The amount crabs ate in the laboratory was negatively correlated to the density of hemolymph protein at the time of collection, which affirms the strong link between nutritional status and hemolymph protein in crustaceans. It also suggests that crabs in good nutritional condition may forgo eating even a high-quality meal if they are stressed. Overall, providing a heterogenous diet did not significantly improve survival rates or affect labile-trait responses in crabs. In contrast, prolonged holding in the laboratory had considerable effects on labile traits: resting metabolic rate (RMR) was highest after one week, but declined over the holding period. There was also a reduction in variation of locomotor activity for approximately 4 weeks. Acute stress responses (increased RMR and activity) also occurred after transfer from holding tanks to experimental chambers, likely due to animal handling. Given the increasing attention paid to animal sentience and welfare, especially for decapod crustaceans, the amount of time that wild crustaceans are held in the laboratory should be considered carefully.