Observations on the feeding behaviour of Nassarius clarus (Gastropoda : Nassariidae) in Shark Bay, Western Australia

Abstract

On a pristine sandflat at Monkey Mia in the World Heritage Site of Shark Bay, Western Australia, lives a single species of nassariid, Nassarius clarus. The inner reaches of Shark Bay are hypersaline, i.e. salinity > 60, but at Monkey Mia, waters are metahaline, salinity ranging from 40 to 45. At Monkey Mia, Nassarius clarus is attracted to, and feeds on, both autochthonous (bivalves) and allochthonous (fish) carrion. A few records of the species attacking other beach inhabitants, including hermit crabs, which it interacts with at carrion, were also obtained. Nassarius clarus is attracted to carrion from a maximum recorded distance of 26 m, reflecting the large scale of such Australian shores. An experiment of disturbing, by scraping, plots of beach sand revealed that N. clarus investigates such areas where it feeds on organic detritus and, presumably, damaged meio- and macrofauna. These feeding observations highlight new facets of nassariid behaviour. That is, first, on such pristine beaches, Nassarius clarus exploits a range of feeding options, from detritivory, to scavenging and the hunting down of damaged 'prey'. On other shores impacted by pollution and dead fish from fishery by-catches, this opportunism has been masked leading to nassariids being considered near-obligate scavengers. Second, the well-known phenomenon of nassariids departing carrion tainted by damaged conspecifics because, it was thought, of a potential threat of predation upon themselves, is here also seen to occur as soon as the bait was touched by the returning tide. Fish predation on such pristine beaches appears to be a real threat but this aspect of nassariid behaviour has again been masked on polluted and (over-) fished beaches by the near absence of significant predators.