The effect of a decrease in salinity on respiration, Osmoregulation and activity in the shore crab,Carcinus maenas (L.) at different acclimation temperatures

Summary

• 1. The rates of oxygen consumption ($\dot V_{{\text{O}}_2 }$) of individual crabs varied with their live mass. Mean$\dot V_{{\text{O}}_2 }$ increased with acclimation temperature in 100% seawater (Q₁₀ 2.36) but not in 50% seawater.

• 2. Exposure to 50% seawater caused a significant increase in$\dot V_{{\text{O}}_2 }$ to twice the rate in 100% seawater at 10°C. There was no significant increase in$\dot V_{{\text{O}}_2 }$ on dilution at 18°C (Fig. 5).

• 3. Heart rate, ventilation volume ($\dot V$) and a-V_{O 2} content difference were unaffected by dilution. The rise in$\dot V_{{\text{O}}_2 }$, following dilution at 10°C may, as far as the cardiovascular system is concerned, arise from an increase in cardiac stroke volume.

• 4. Crabs were isosmotic with 100% seawater at 10°C, 14°C and 18°C. In 50% seawater all crabs showed a significant reduction in blood osmolarity, though they maintained the ΔF.p. and Na⁺ concentration significantly above that of the medium. Crabs acclimated to 10°C maintained a significantly higher blood ΔF.p. and Na⁺ concentration in 50% seawater than crabs at 18°C (Fig. 6).

• 5. Crabs acclimated to 10°C were significantly more active after exposure to 50% seawater. There was no significant change in activity, following dilution, in crabs at 18°C (Fig. 7).

• 6. The variations in$\dot V_{{\text{O}}_2 }$ with temperature and salinity seem to relate to the measured changes in patterns of osmoregulation and activity. At 10°CCarcinus osmoregulates more effectively than at 18°C and is hyperactive in low salinities, which may represent an avoidance reaction. At 18°C, the summer temperature, the crab tolerates internal dilution and is relatively quiescent.