Ecological Observations on Cerithium moniliferum Kiener (Gastropoda : Cerithiidae) and its Trematode Parasites at Heron Island, Great Barrier Reef

Abstract

The distribution, abundance, growth and reproduction of a population of tropical intertidal gastropods, Cerithium moniliferum, at Heron Island, Great Barrier Reef, were examined and related to the incidence of parasitism by 11 digenean trematodes. The snails were patchily distributed on exposed beachrock, and showed little seasonally related change in abundance, but numbers and shell morphs were correlated with sand movements. Snails bred mainly in spring, had a thickened lip to the body whorl at this time and grew mainly from summer through winter, migrating to higher more exposed levels as they grew. There were no seasonal patterns of incidence with any or all trematodes, five of which were moderately common, though rarely did incidence exceed 20% of the population. Parasitism was more common in larger snails with thick lips and eroded shells found at the higher levels of the beachrock. Parasitism presumably steadily increases with age and size, but once infected, snails stop growing. Parasitized snails are castrated and presumably live for about 2-3 years by which time infection rates exceed 50%.