Physiological responses of postprandial red rock crabs (Cancer productus) during emersion

Abstract

The physiological responses of unfed and postprandial red rock crabs ( Cancer productus J.W. Randal, 1840) were investigated during periods of emersion. During aerial exposure, oxygen uptake quickly fell to very low levels and was no longer detectable in the haemolymph after 12 h. The resulting anaerobic respiration led to a build up in lactic acid and the resulting acidosis was more pronounced in the postprandial crabs. There was also a concomitant rise in PCO2and CCO2, and in both cases these were higher in postprandial animals. Higher ammonia levels in postprandial crabs showed that cellular activities were still proceeding anaerobically, suggesting that although crabs can delay mechanical digestion during emersion, once intracellular digestion occurs they may be committed to these processes. Increased mortality rates of postprandial animals were probably due to a combination of the high lactate and CO2levels coupled with an increased ammonia concentration. For C. productus stranded in the intertidal zone there may be little effect of feeding, as they are only exposed for short periods and recovery occurs during re-immersion. The crabs are more likely to become moribund and death ensue during longer term exposure such as commercial live shipment.