In situ studies on physiology and behaviour in two colour forms of the shore crab Carcinus maenas in relation to season

Abstract

Heart rate and locomotor activity were monitored continuously in situ in male green and red colour forms of the shore crab Carcinus maenas along with simultaneous recordings of light intensity, temperature, depth and salinity in the shallow, weakly tidal Isefjord, Denmark. Experiments were conducted during 2 seasons, summer and late autumn. Circatidal and/or circadian rhythmicity in heart rate and/or locomotor activity was observed in 87 % of all crabs during summer and in 55 % of all crabs during autumn. During summer, 45 % of the green crabs and 17 % of the red crabs had significantly higher heart rates during high tide than during low tide. During autumn, 30% of the green crabs had significantly higher heart rates during high tide than during low tide (p <0.05 This was never observed in red crabs. Furthermore, 45 % of green and 42 % of red crabs expressed a diurnal variation in heart rate during summer. During autumn, this was observed in 40 % of the green and 30 % of the red crabs. For both colour forms, heart rate levels were significantly higher during summer than during autumn (p <0.001). For the temperature interval 4 to 25°C, Q 10 for heart rate was 2.14. No significant difference was observed between colour forms. A tight coupling was found between heart rate and locomotor activity, heart rate increased at times with increased locomotor activity. Temperature was the abiotic variable found to exert the largest influence on heart rate and locomotor activity, followed by depth, light and salinity.