Seasonal and Geographical Differences in Oxygen Consumption with Temperature ofCerastoderma glaucum(Poiret) and a Comparison withC. edule(L.)

A comparison was made of the oxygen consumption over the temperature range 5–45 °C ofCerastoderma glaucum(Poiret) with season [summer (S) and winter (W)] and with latitude [Ireland (I), France (F)]. Maximum oxygen consumption rates for IW, IS, FW and FS groups were measured at 10–20 °C, 20–30 °C, 15–25 °C and 20–35 °C, respectively, reflecting the differences in the water temperatures at the time of collection of 5•5, 21•0, 6•7 and 23•5 °C respectively. Upper temperature limits were estimated at between 40 and 45 °C for the FS, FW and IS groups and between 35 and 40 °C for the IW group. The oxygen consumption rates of both the summer groups were substantially lower than the winter rates at the same temperature, indicating a considerable degree of reverse acclimation. However the rates of the French (FW, FS) groups were lower at low temperatures, but consistently higher at high temperatures than those of the Irish (IS, IW) groups, indicating no latitudinal compensation. A major difference, that is the restriction of the Irish (IS, IW) population to one age cohort compared to at least three in the French (FS, FW) population was confirmed. Overall, the French animals, especially the smaller individuals, were slightly heavier (dry flesh weight) than their Irish counterparts. In comparison withCerastoderma edule(L.),C. glaucumhad markedly lower oxygen consumption rates at high temperatures in both summer groups, although the distinction was much less clear in the winter groups. High summer temperatures in lagoons and similar habitats could therefore be a major factor separating the distributions of the two species.