SEASONAL AND GEOGRAPHICAL DIFFERENCES IN OXYGEN-CONSUMPTION WITH TEMPERATURE OF CERASTODERMA-GLAUCUM (POIRET) AND A COMPARISON WITH C-EDULE(L.)

A comparison was made of the oxygen consumption over the temperature r ange 5-45 degrees C of Cerastoderma glaucum (Poiret) with season [summ er (S) and winter (W)] and with latitude [Ireland (I), France (F)]. Ma ximum oxygen consumption rates for IW, IS, FW and FS groups were measu red at 10-20 degrees C, 20-30 degrees C, 15-25 degrees C and 20-35 deg rees C, respectively, reflecting the differences in the water temperat ures at the time of collection of 5.5, 21.0, 6.7 and 23.5 degrees C re spectively. Upper temperature limits were estimated at between 40 and 45 degrees C for the FS, FW and IS groups and between 35 and 40 degree s C for the IW group. The oxygen consumption rates of both the summer groups were substantially lower than the winter rates at the same temp erature, indicating a considerable degree of reverse acclimation. Howe ver the rates of the French (FW, FS) groups were lower at low temperat ures, but consistently higher at high temperatures than those of the I rish (IS, IW) groups, indicating no latitudinal compensation. A major difference, that is the restriction of the Irish (IS, IW) population t o one age cohort compared to at least three in the French (FS, FW) pop ulation was confirmed. Overall, the French animals, especially the sma ller individuals, were slightly heavier (dry flesh weight) than their Irish counterparts. In comparison with Cerastoderma edule (L.), C. gla ucum had 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 ha bitats could therefore be a major factor separating the distributions of the two species. (C) 1997 Academic Press Limited.