Factors Affecting the Respiration of Intertidal Invertebrates

Abstract

The nature and rate of gas exchange in intertidal organisms is variable and is the product of an extremely complex environmental situation. Such influences may be grouped into tidal-dependent factors such as the proportion of time spent exposed to air, the magnitude of environmental temperature fluctuations, and the availability of food. Factors which may be regarded as generally operating independently of tidal level include latitudinal variations in environmental temperature. Superimposed upon such spatial environmental variations are seasonal factors such as temperature and photoperiod, which impose a temporal cycle upon the metabolic rate. Finally, there are numerous endogenous factors such as body size, activity level, and stage of development which profoundly influence the rate of respiration. It can be shown that some factors, such as aerial or aquatic conditions, may affect respiration qualitatively. Under aquatic conditions gas exchange is with the surrounding sea water, but with increasing exposure to air intertidal invertebrates are able to respire aerially and to withstand the water loss associated with this process. Many are also able to respire anaerobically under conditions of stress. In contrast, factors such as activity level, body size, nutritional conditions, and exposure temperature affect respiration quantitatively and are often interdependent. The metabolism of intertidal animals is then endowed with considerable flexibility between the extremes set by the active and standard rates of respiration. This active rate of respiration is markedly temperature-dependent in most instances, whereas the standard rate, which is characteristic of quiescent animals, is not only lower but often has a low temperature coefficient. A reduction in respiration conserves metabolic reserves during periods of stress, and the low temperature coefficient further minimizes depletion of such reserves despite the high environmental temperatures which often prevail during the intertidal period.