Respiratory metabolism of crabs from marine and estuarine habitats: an interspecific comparison

The gill-surface area and R-T (metabolic rate-temperature) response during aquatic and aerial respiration of three different species of crabs, the subtidal Scylla serrata, the intertidal Sesarma quadratum, and the supratidal Ocypoda platytarsis, were compared. Scylla serrata has the highest, Sesarma quadratum the second highest, and O.platytarsis the lowest gill-surface area. Oxygen-consumption values in water under different ambient partial pressures of oxygen indicate that all three species display equally efficient aquatic respiration despite variation in gill area and number. There is no coherent R-T response either inter- or intra-specifically. However, the ability to extract oxygen from the surrounding medium (respiratory efficiency) conditions the R-T response in the different species. The R-T trends in aquatic respiration of Scylla serrata and aerial respiration of O.platytarsis reveal a normal response to temperature. The proportion of aquaticoxygen uptake to total respiration in all sizes in both Scylla serrata and Sesarma quadratum remains more or less constant (between 88 and 92%), whereas in the supratidal O.platytarsis, this proportion decreases with increasing weight (from 88 to 64 %), indicating a progressive loss of gill respiration to total respiration. All three species are metabolically equally efficient; what one lacks in respiratory surface it compensates by respiratory efficiency.