The distribution of the intertidal rock pool prawn Palaemon elegans Rathke, on a rocky shore of the Isle of Cumbrae in west Scotland, was investigated. Prawns of all sizes were abundant in the mid- to high-shore pools throughout the summer until September when the largest individuals began to dissappear from the shore. Small and large P. elegans were found to be distributed on the shore in different ways. The small prawns found on the shore during the winter exhibited a much altered behaviour. In the laboratory, the effect of temperature change on oxygen consumption was assessed as was the role of temperature acclimation in determining the rate of oxygen consumption. Oxygen consumption calculated as a weight specific rate (Mo2) could be negatively correlated with body weight. This relationship between body weight and oxygen consumption was different in prawns acclimated to 10 and 23 degrees C and is considered to be an acclimatory response. The acute response, of prawns acclimated to a given temperature, to changes in temperature was similar in different sized prawns. After an acclimatory period of between 1 and 2 weeks small prawns exhibited positive acclimation of oxygen consumption whereas the larger prawns appeared to be unable to acclimate. This variable size dependent, response is discussed as a determinant of distribution and behaviour.