Tidal activity rhythms in the mangrove snail Cerithidea decollata (Linn.) (Gastropoda: Prosobranchia: Cerithiidae)

Abstract

Activity rhythms in Cerithidea decollata which migrates between the trees and the substrate in south-east African mangrove swamps were investigated in Durban Bay, South Africa. No light/dark rhythms were found. Activity followed a 14-day tidal rhythm. Maximum activity occurred over neap-tide periods and least over spring-tide periods when snails tended to remain on the trees over both high and low tides. Snails descended to the substrate more frequently in the upper inter- tidal area where inundation was less frequent and of shorter duration. Descent to the substrate appears to be associated with feeding. Tree-climbing is suggested to be a predator- avoidance mechanism.