Some responses of the shore crab,Carcinus maenas (L.) to progressive hypoxia at different acclimation temperatures and salinities

Summary

• 1. TheP _IO₂ at which crabs emerged from shallow seawater during progressive hypoxia (Table 1), as well as theP _c levels for$\dot V_{O_2 }$ (Fig. 2) and$\dot V_g$ (Fig. 4) of submerged crabs, increased with acclimation temperature and following exposure to 50% seawater at low temperatures (Fig. 6). This pattern of variation resembles the changes in relative oxygen demand with temperature and salinity.

• 2. TheP _c levels for heart rate increased with acclimation temperature but were unaffected by dilution (Fig. 6).

• 3. Percentage extraction of oxygen from the respired water (Table 2) as well as the levels of motor activity (Fig. 5) were not affected by exposure to hypoxia.

• 4. Lactic acid concentration in the blood of submerged crabs increased markedly during hypoxia and there was an enhanced$\dot V_{O_2 }$ on recovery in normoxia (Fig. 2), which apparently served to completely repay an accumulated oxygen debt.

• 5. It was concluded that when exposed to environmental hypoxiaCarcinus can adopt the alternative strategies of either accumulating an oxygen debt when in deep water or emerging into air from shallow water to aerate the branchial chambers.