Respiration in air and water of intertidal gastropods
Many high shore gastropods maintain aerobic metabolism during aerial exposure at a level similar to that in seawater. These amphibious species generally have temperature dependent Q10 values in air and water and an aerial aerobic scope for activity similar to that in seawater. Cost of transport is higher in air than water. In contrast, many low shore species have depressed rates of oxygen consumption while exposed in air. This is correlated with temperature independent aerial Q10 values and little or no aerobic scope for activity in air. All ten gill-bearing species hold a significant amount of fluid within the mantle cavity during aerial exposure. Loss of this fluid leads to a decrease in aerial oxygen consumption. Comparisons of (i) the respiration rates of the Mediterranean and Cool Temperate gastropods at 20°C and (ii) the estimates of total daily oxygen consumption of species from both latitudes, revealed no evidence of thermal acclimation. Depressed rates of oxygen consumption are reported for the Cool Temperate gastropods during winter. This is an example of reverse acclimation. Those high shore gastropods which are well adapted for aerial respiration can survive for longer periods in air than the primarily aquatic low shore species. Comparisons are made between the aquatic to aerial ratios, temperature coefficients, weight exponents, costs of transport and aerobic expansibilities reported for gastropods and those of other groups of marine, intertidal and terrestrial invertebrates. The main findings of this investigation are summarised in Tables 11.1 and 11.2.