Specific dynamic action in the shore crab, Carcinus maenas (L.), in relation to acclimation temperature and to the onset of the emersion response.

The rate of oxygen uptake (MO(2)) of shore crabs following a period of fasting varied directly with acclimation temperature, with a Q(10) of 2.96 between 7 degrees and 15 degrees C and a Q(10) of 2.11 between 15 degrees and 22 degrees C. The factorial rise in MO(2) following a meal (specific dynamic action [SDA]) ranged between 1.9 and 3.1 and varied with temperature, being highest at 15 degrees C and significantly lower at both 7 degrees and 22 degrees C, despite similar ration sizes in all groups. At 7 degrees C, the SDA coefficient and magnitude were significantly lower than at 15 degrees C, possibly due in part to the inhibition of protein synthesis. Both the time to peak and the duration of the SDA response were inversely related to temperature. SDA coefficients were inversely related to the amount of food consumed. The critical oxygen tension of inspired water (P(I)O(2)), which evoked the emersion response in fasted animals, increased with temperature and further increased at each temperature when the animals were fed. Thus, the threshold P(I)O(2) evoking the emersion response is directly related to relative metabolic oxygen demand in Carcinus.

Protein synthesis and specific dynamic action in crustaceans: effects of temperature.

Temperature influences the specific dynamic action (SDA), or rise in oxygen uptake rate after feeding, in eurythermal and stenothermal crustaceans by changing the timing and the magnitude of the response. Intra-specific studies on the eurythermal crab, Carcinus maenas, show that a reduction in acclimation temperature is associated with a decrease in SDA magnitude, resulting from an increase in SDA duration but a decrease in peak factorial scope (the factorial rise in peak SDA over prefeeding values). Inter-specific feeding studies on stenothermal polar isopods revealed marked differences in SDA response between the Antarctic species, Glyptonotus antarcticus and the Arctic species, Saduria entomon. Compared to S. entomon held at 4 and 13 degrees C, the SDA response in G. antarcticus held at 1 degrees C was characterised by a lower absolute oxygen uptake rate at peak SDA and an extended SDA duration. At peak SDA, whole animal rates of protein synthesis increased in proportion to the postprandial increase in oxygen uptake rate in the Antarctic and the Arctic species. Rates of oxygen uptake plotted against whole animal rates of protein synthesis gave similar relationships in both isopod species, indicating similar costs of protein synthesis after a meal, despite their differences in SDA response and thermal habitat.