Baseline measurements of physiological and behavioural stress markers in the commercially important decapod Cancer pagurus (L.)

Increasing human activities in marine environments pose possibilities of new stressors affecting marine invertebrates important for fisheries. However, assessment of such stressors is hampered by lack of baseline information on stress markers in relevant species, particularly relating to potential diel rhythms. Cancer pagurus is the second most important crustacean for UK fisheries and, owing to its migratory habits, is likely to encounter anthropogenic stressors both inshore and offshore. However, there are no baseline measurements of commonly used stress markers in this species, particularly on juveniles, nor data on diel variations. This study aimed to establish baseline data for several stress components in C. pagurus: haemolymph l-Lactate, d-Glucose, Haemocyanin, haemolymph density and respiration rate, as well as behavioural indicators (activity level, antennular flicking rate) during day and night. l-Lactate and d-Glucose concentrations were positively related to crab size, larger crabs having higher concentrations. l-Lactate and d-Glucose levels followed similar circadian rhythms increasing towards dusk, coinciding with higher locomotor activities. l-Lactate levels in juvenile crabs showed a significantly different pattern compared to larger crabs, with lower concentrations maintained throughout the day without any significant increase at dusk. Haemocyanin concentration and haemolymph density were not affected by crab size, sex or time. However, females (0.06 ± 0.01 mg/g/h) consumed significantly more oxygen than males (0.04 ± 0.01 mg/g/h). Activity levels increased significantly at night when foraging mainly occurs. Small crabs were more active, but had lower antennular flicking rates compared to medium and large crabs during both day and night. The present work shows that crab size and sampling time influence the value of commonly used crustacean stress markers, suggesting that these factors should be incorporated into any studies monitoring stress responses of Cancer pagurus.