Behaviour
Littoraria scabra is a widespread species of marine snail that typically lives on the trunks, prop roots and lower branches of mangrove trees.
These snails remain above the surface of the sea at all times, and are effectively terrestrial, respiring in air by means of the air-filled mantle cavity with reduced gill folds. If animals are contacted by a rising tide they move upwards to avoid submersion, and then follow the retreating tide downwards, grazing as they go.
They are active mainly at night and after rain. Females occasionally move down to the water surface to release their larvae, probably once a month during high spring tides. Like all intertidal littorinids, when animals have been dry for several days they withdraw into the shell and remain attached to the substrate by a film of dry mucus. The foot is not suited to locomotion on sand or mud, and the animals remain on hard substrates at all times.
The shell of these arboreal snails is relatively thin and they are therefore susceptible to attack by shell-crushing predators, principally crabs but also molluscivorous fish. Indeed, such is the intensity of crushing predation in mangrove habitats that this may have contributed to the selective pressure to adopt a tree-dwelling habit early in the evolution of the genus.
Most shells of L. scabra show evidence of previous attack by crabs, in the form of repaired shell breakages that appear as jagged scars. Such scars indicate that the animal survived attack and then continued shell growth. At a site in north Queensland the average number of such unsuccessful attacks was recorded as 3 per shell. The most numerous molluscivorous crab predators in mangrove habitats in the Indo-Pacific are grapsids of the genus Metapograpsus, which can climb for 5 m into the tree canopy. Other shell-crushing crabs include the portunids Scylla and Thalamita, but these are swimming crabs that do not climb above the water.