Locomotor activity patterns of the mangrove littorinids, Littoraria ardouiniana and L. melanostoma, in Hong Kong

Abstract

Littoraria ardouiniana and L. melanostoma are common in Hong Kong mangrove forests. The locomotion of these snails is constrained to their host trees and, therefore, affected by physical factors experienced in the tree canopy. To investigate factors that affected the activity of these Littoraria species, in situ observations and experiments were conducted. Observations suggested that the littorinids were inactive in daytime, except when it rained, and active at night, even without stimulation by rain. All littorinids crawled downwards when they started moving in the evening and returned close to their initial height after their activity period. Spraying with freshwater to simulate rain initiated movement. Since most individuals were located above the high water mark and subject to terrestrial conditions, the littorinids were not influenced by tidal change on a daily basis, but were activated by rain. It appears that physical factors, most likely desiccation stress, strongly influence the activity patterns of these two littorinid species within the mangrove tree canopy.