Assessment of factors affecting heart rate of the limpet Patella vulgata on the natural shore

Heart rate variations of a population of the limpet Patella vulgata were mo nitored in the natural environment (Lough Hyne, southern Ireland) by noninv asive, optoelectronic recording. The heart rates of 145 limpets of differen t sizes, living on vertical and horizontal substrata, were measured both in air and water at different environmental temperatures, while the animals w ere inactive on their home scars. The heart rates of emersed, inactive limp ets were positively related to air temperature and negatively related to li mpet size. These relationships were similar for limpets on vertical and hor izontal substrates. In contrast, no significant relationship between heart rate and temperature was found in submerged limpets, probably due to the na rrow thermal range of the water during the study period. During submersion, a significant negative relationship between heart rate and size was eviden t for limpets on vertical surfaces but not for limpets on horizontal surfac es. In general, submerged limpets had a higher heart rate, 1.16 times that of limpets exposed to air. Moreover, the heart rates of nine animals were r ecorded while they were moving and while inactive on their home scars. Acti ve limpets had a faster heart rate, 1.6 times that of limpets resting on th eir home scars. The dependence of heart rate on environmental temperature, size, respiratory medium and activity, as observed in limpets on the shore, agrees well with laboratory data and with previous findings of the correla tion of oxygen consumption with the same factors. Such in situ measurements may, therefore, prove useful in attempts to determine natural levels of en ergy expenditure in models on the behaviour of foraging molluscs.