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

Abstract

Activity rhythms in Cerifhidea decol/afa which migrates between the trees and the substrate in southeast 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. S. AIr. J. Zoot. 1981,16: 5-9 Aktiwiteitsritmes van Cerifhidea decol/afa wat migreer tussen bome en die grondlaag in Suid-Afrikaanse wortelboom-moerasse is in Durban-baai, Suid-Afrika, ondersoek. Geen IIg/ donker ritmes kon gevind word nie. Aktiwiteit was volgens 'n 14-daagse getyritme. Maksimumaktiwiteit het met ebgety plaasgevind en minimumaktiwiteit met springgety, wanneer slakke in die bome gebly het met beide hoogwater en laag-water. Siakke het meer dikweis na die grondvlak afgekom in die ho&r tussengety-gebied, waar oorspoeling minder dikwels en vir korter periodes voorgekom het. Die afkom na grondvlak hou skynbaar verband met voeding, en boomklim vermoedelik met ontwyking van roofdiere. S.-Afr. Tydskr. Dierk.