Respiratory properties of the haemolymph of the intertidal prawn <i>Palaemon elegans</i> (Rathke)

Abstract

Abstract The properties of the haemolymph of Palaemon elegans for oxygen and carbon dioxide transport were studied with respect to the considerable fluctuation in the environmental conditions normally experienced by this prawn in intertidal rock pools. The haemolymph was found to have a high oxygen affinity (P 50 = 3.6 Torr, 15°C, pH 8.0) and a large oxygen carrying capacity (1.17 mmol.L −1 ), as well as a marked Bohr shift (φ = ‐ 1.7). Under some conditions, the affinity appeared to be independent of temperature as did the n 50 value (n 50 = 2.8). Experiments in which the pH of the haemolymph was varied using fixed acid together with two different CO 2 tensions demonstrated a specific CO 2 effect on O 2 affinity, which did not affect the Bohr factor. The nonbicarbonate buffer value of the haemolymph was found to be high (16.02 mmol.L −1 .pH unit −1 ). The in vivo postbranchial haemolymph pH at 15°C was 7.89 with a calculated Pco 2 of 1.26 Torr. A large functional Haldane coefficient was observed (1.25), which was only moderately temperature dependent. The haemolymph exhibited an extremely high capacitance for CO 2 at low Pco 2 values (βCO 2 = 8.4 mmol.L −1 .Torr −1 ). Some functional implications of linkage between the large Bohr and Haldane effects are discussed in light of present knowledge.