A laboratory study of the behavioural responses of Littorina Neritoides (Mollusca: Gastropoda) in relation to its zonation on Maltese shores (Central Mediterranean)

Abstract

Littorina neritoides is the dominant supralittoral gastropod on the microtidal rocky shores of the central Mediterranean. The snails spend the hot dry summer months in dense aggregates in pits or under overhangs and are completely inactive. Inactive snails are activated by wetting with seawater. A high relative humidity did not activate the snails either alone or in combination with mechanical stimulation. Dry inactive snails took a significantly longer time to become active following wetting with seawater than similar snails that were mechanically stimulated immediately prior to wetting, showing that mechanical stimulation enhances the activating effect of seawater. When immersed in seawater, snails moved up vertical surfaces until emersed. Water depth had no effect on the speed of upwards movement but the presence of underwater crevices retarded the rate of emersion of snails. A low RH caused the snails to distribute themselves closer to the water surface than when the RH was high. Snails moving out of water and onto a pitted surface tended to stop moving sooner than snails emerging onto a smooth surface. Light did not have any effect either on the rate of emersion of submerged snails or on distribution pattern after emersion. The functional significance of these results is discussed in relations to the spatial and temporal patterns of zonation of L. neritoides.