Metabolic costs of the mechanical components of the apparent specific dynamic action in the Dungeness crab, Cancer magister

The specific dynamic action (SDA) describes the postprandial increase in metabolism. It is a composite of mechanical and chemical digestion, nutrient transport and protein synthesis. How these individual events contribute to the overall SDA has not been worked out fully for any organism. The mechanical events associated with the SDA were investigated in Dungeness crabs, Cancer magister. Following consumption of a meal, oxygen consumption (MO2) remained elevated for several hours. When the crabs were presented with fish scent there was a 2 fold increase in MO2, which rapidly decreased once the stimulus was removed. Crabs were then offered fish in a perforated tube. There was a rapid increase in MO2 associated with handling which returned to pre-treatment levels within an hour of removal of the tube. Finally the crabs were fed a piece of foam that had been soaked in fish water to determine the costs of mechanical digestion. The mechanical breakdown of the meal accounted for 29.9 ± 3.3% of the overall SDA. Since food handling produced a large increase in MO2, it was reinvestigated using crabs that had one or both claws removed. Although there were no statistically significant differences as a function of claw removal there was a consistent trend in the data. The maximum MO2, scope, duration and SDA increased from animals with 0 claws through 1 claw to 2 claws. The results showed that the mechanical portion of the SDA can account for a significant portion of the overall budget in decapod crustaceans.