Energetically defining the thermal limits of the snow crab

The snow crab, Chionoecetes opilio, is a cold-water species found naturally at temperatures below 5 °C. Its physiology and energetics were examined to understand the metabolic limitations that restrict the snow crab to these temperatures. The species is not confined to cold water because of a limited respiratory system. Routine oxygen demand can be met even at lethal temperatures of 18°C (56mgO2kg−1h−1, with a Q10 of 2·2). Blood lactate levels remain below 1·5 mmol 1−1 and actually decline slightly with temperature. Energy budgets, which were constructed from an examination of oxygen uptake, activity and food consumption in morphometrically mature male animals between 0 and 18 °C, indicate that the snow crab is energetically restricted to cold water. Rising metabolic costs overtake caloric intake around 7 °C. This is probably due to digestive metabolism which is temperature-sensitive. Food consumption increases up to 6°C but then falls. Crabs stop feeding above 12°C. Although the growth equation is positive between 1 and 7°C, it becomes slightly negative below 1°C. This observation is unexpected since snow crabs are commonly found between 0 and 1 °C. Slight temperature changes in the natural environment may, therefore, regulate growth and reproduction in this species.