IN-SITU VARIATION IN HEART-RATE OF THE SHORE CRAB CARCINUS-MAENAS IN RELATION TO ENVIRONMENTAL-FACTORS AND PHYSIOLOGICAL CONDITION

Heart rate of Carcinus maenas was recorded continuously for two days i n situ, together with water temperature, salinity, depth and Light int ensity. Of each sex, 25 crabs were used and assigned to groups on the basis of size and colour (the carapace changes colour with prolongatio n of the intermoult phase). Wet weight:dry weight ratios of midgut gla nd, muscle, gonads and whole body were examined together with midgut g land lipid content and haemolymph protein concentration. Heart rates a nd wet wt:dry wt ratios for all the tissues examined were higher in ea rly intermoult than in late intermoult stages of the adult C. maenas ( P < 0.05). Heart rate, lipid content and haemolymph protein concentrat ions were higher and wet wt:dry wt ratios of midgut gland, gonads and whole body were lower in juvenile crabs than in adults (P < 0.05). The relationship between heart rate and wet wt:dry wt of whole body diffe red among C. maenas in early and late intermoult. Heart rate was posit ively correlated with midgut gland lipid content (a Darwinian fitness parameter) in crabs that were in late intermoult. Physico-chemical env ironmental parameters, sex and colour accounted for 12% of the variati on in heart rate of C. maenas recorded 12% situ, Temperature and prolo nged intermoult were the most important factors influencing heart rate . The findings are discussed in relation to laboratory studies of card iac activity and observed behaviour of C. maenas in the field.