The provision of oxygen to developing eggs by female shore crabs (carcinus maenas)

In shallow hypoxic sea water female shore crabs (Carcinus maenas (L.)) incubating eggs on their abdominal pleopods reverse the direction of normal ventilation, taking air in at the normally exhalant opening and bubbling it out via apertures at the base of the posteriormost pair of walking legs and hence over the developing egg mass. The ambient oxygen tension at which the behaviour is elicited and the percentage of total time it is performed are both dependent upon acclimation temperature. The oxygen tension at which the behaviour is first observed coincided at different acclimation temperatures with the critical oxygen tension below which oxygen consumption of the developing eggs became dependent on further reduction in P0. The bubbling of air during the emersion response is sufficient to raise the oxygen tension of the water surrounding the eggs and is thus an attempt by the parent animal to maintain the oxygen uptake of the developing young. If left in a standing body of hypoxic sea water release of larvae is deferred until well-aerated conditions next prevail. Thus if the berried female is trapped in a rock pool the encroaching tide may act as a releasing stimulus which is of adaptive significance to the dispersal and survival of the larvae. When female crabs submerged in warm water (25 °C) bubbled cool air past the egg mass this had no significant cooling effect. The thermal tolerance of the developing eggs was low, rate of oxygen uptake being limited by temperature rises above 25 °C.