Predation by Natica maculosa Lamarck (Naticidae: Gastropoda) upon the trochacean gastropod Umbonium vestiarium (L.) on a Malaysian shore

Abstract

About 1.2 · m −2 Natica maculosa Lamarck on Penang sandy shores feed entirely by drilling Umbonium vestiarium (L.) occurring at densities often exceeding 10000 · m −2. Consumption reached 1.5 Umbonium · Natica −1 · day −1 in fast growing young Natica and was a mean 1.27 Umbonium · Natica −1 · day −1 in adult Natica > 16 mm in shell height. Natica drilled more and larger Umbonium as it grew and well-grown specimens selected shells of diameters > 10 mm rather than taking prey at random. Accordingly, tissue consumption rose to 0.029 g dry wt · Natica −1 · day −1 in nearly full grown animals, falling slightly in adults > 16 mm. Daily tissue growth increments also reached maxima in Natica of 12–14 mm shell height. Gross growth efficiency reached 21.9% at shell heights of 10–12 mm while consumption as a proportion of body weight fell sharply throughout growth. It is suggested that lack of Umbonium > 13 mm shell diameter might have limited consumption in larger Natica but that Umbonium is a more economic food source than the thicker-shelled Donax faba Gmelin which lived in a separate zone of the same shores. On the shore, consumption is estimated at 623 Umbonium (11.9 g dry tissue) · m −2 · yr −1 and Natica production by growth at 0.74 g dry tissue · m −2 · yr −1 in a biomass of some 0.3 g dry tissue · m −2. The application of these values is limited by the short duration of the study (July–September 1981) and the likelihood of significant annual changes in prey and predator.