Physiological ecology ofPatella. II. Effect of environmental acclimation on the metabolic rate

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Abstract
The physiological basis for the previously reported differences in the rate of respiration between high-shore-level and low-level populations ofPatella vulgatain the summertime has been investigated in relation to distribution differences between this species andP. aspera.The respiration rate of bothP. asperaand low-levelP. vulgatais low in the winter but increases in the spring to a level which is maintained until the post-spawning period in the autumn. The respiration rate of high-levelP. vulgatadoes not increase in the spring but remains at the low winter level. The inter-population difference in rate of respiration therefore appears in the spring and is maintained until the autumn.The difference in rate of respiration cannot be accounted for by differences in the amount of non-respiring tissue in equal weight individuals and is phenotypic and not genotypic, as indicated by transplantation experiments. These experiments also rule out the possibility of differences in age of equal weight individuals from the two populations being responsible.Respiration rate was found to be a function of both intertidal height and of the abundance of algal food in the habitat. It is suggested that the low-level population ofP. vulgatashould be regarded as the normal form and that the low respiration rate of high-level limpets in the summer represents a form of adaptation to the stresses of their habitat. It is possible that both nutritional level and temperature acclimation are important in this, and it is speculated that inability to reduce the level of metabolism may be one factor preventing the colonization of high-shore-level habitats byP. aspera.