THE CLIMBING BEHAVIOR OF CERITHIDEA-ANTICIPATA (MOLUSCA, GASTROPODA) - THE ROLES OF PHYSICAL AND BIOLOGICAL FACTORS

Many molluscs in tidal wetlands climb trees as the tide rises, a behav iour usually assumed to be a means of avoiding subtidal predators. Som e species are more active during neap tides, when the access of subtid al predators to the forest is limited, but rest on trees during spring tides. Cerithidea anticipata, which inhabits the mangrove forests aro und Darwin Harbour (Northern Territory, Australia), displayed almost e xactly the opposite pattern. This species climbed higher, and was less active, during neap tides that did not flood the forest than during s pring tides. Tn experiments with tethered snails, individuals prevente d from climbing died during neap tides, apparently from physiological stress. Further, individuals resting on trees around clearings, usuall y selected shaded sites. These results suggest that the major reason C . anticipata climbed was to avoid physiological stress during neap tid es, not subtidal predators during spring rides. There was some evidenc e of predation under the canopy, but the rate was relatively low and t he species responsible appeared to be resident in the forest.