ECOLOGICAL ENERGETICS OF MUSSELS CHOROMYTILUS-MERIDIONALIS UNDER SIMULATED INTERTIDAL ROCK POOL CONDITIONS

Organisms isolated in intertidal rock pools during ebb tide are frequently subject to elevated temperature and O2 tension by day and reduced O2 levels by night. The effects of these conditions on metabolic energy balance in 50-mm mussels Choromytilus meridionalis were investigated in the laboratory. Respiration rates increased with temperature between 12.5 and 30 °C and also with increasing O2 tension at each temperature. Filtration rates were generally independent of O2 tension but decreased from ≈ 1.91 · h-1 at 12.5 °C to 0 at 30 °C. Absorption efficiency was unaffected by O2 tension but appeared to decrease with rising temperature. Exposure to elevated temperature and O2 tension can thus result in a rapid deterioration of energy balance. In isolated rock pools, this situation is further aggravated by the depletion of available food supplies, especially if this is not accompanied by any compensatory depression of filtration or respiratory activity. By contrast, the same mussels can reduce their metabolism to 11% of the submerged rate during aerial exposure and this rate is temperature-independent. Exposure to air is thus energetically less costly than isolation in a rock pool. It is concluded that the upward penetration of rock pool populations of C. meridionalis may be limited by energy balance whereas that of aerially exposed populations is probably restricted by resistance to desiccation. © 1990.