Predator-prey interactions between Lepsiella vinosa (Gastropoda: Muricidae) and Xenostrobus inconstans (Bivalvia: Mytilidae) in a southwest Australian marsh

Abstract

At Shoal Bay, Princess Royal Harbour, Albany, in southwestern Australia, at the western extremity of its range, the muricid Lepsiella vinosa feeds monotonically, mostly by drilling, on the mussel Xenostrobus inconstans. Because it lives anterior down in a mat of byssal threads, the mussel is attacked posteriorly by L. vinosa. In laboratory experiments, however, attacks were predominantly anterior, above the visceral mass. Xenostrobus inconstans has an intertidal vertical range that extends from within a supralittoral marsh of rushes and sedges down into the seaward eulittoral zone, but was most abundant above and below the marsh margin. Sympatric with X. inconstans but most numerous at the marsh margin, is another mussel, the larger, strongly ribbed Brachidontes erosus which L. vinosa rarely attacks. The intertidal range of L. vinosa matches that of the two mussels and the field preference for X. inconstans was confirmed by laboratory experiments in which it was consumed first, followed over a much longer time interval by attacks on B. erosus. Laboratory experiments further revealed that L. vinosa has a size preference for X. inconstans of between 10 and 20 mm, the largest individuals (25 mm) being less frequently attacked and small ones (5 mm) more rarely, except when all others have been consumed. In southeastern Australia, L. vinosa feeds on littorines and barnacles in mangroves, and on barnacles, tube-building polychaetes and mussels on rocky shores. Throughout its wide longitudinal range Lepsiella vinosafeeds, typically high on the shore, by drilling littorines, barnacles or mussels. It can attack its prey when immersed or, less frequently, emersed and both by drilling and marginal access with its proboscis. Longitudinal differences in prey choice are related to community differences in prey availability.