2 B
. Morton, W.Y. Yuen J. Exp. Mar. Biol. Ecol. 246 2000 1 –29
edwardsii increased and the number of N . festivus decreased, the number of intraspecific
interactions in the former increased. The feeding time of N . festivus, however, decreased with
increasing numbers of conspecifics and a decreasing number of D . edwardsii. This suggests the
possibility of intraspecific competition in N . festivus.
2000 Elsevier Science B.V. All rights
reserved.
Keywords : Competition; Diogenes edwardsii; Feeding behaviour; Interactions; Nassarius festivus; Scavengers
1. Introduction
Marine scavengers feed on ephemeral carrion Britton and Morton, 1994a. Studies on the feeding behaviour of scavengers on sandy shores in Hong Kong have focused on the
Nassariidae Gastropoda. A well-studied representative of this family is Nassarius festivus Powys Morton, 1990; Britton and Morton, 1992, 1993, 1994a; Cheung, 1994,
1997 which feeds on moribund bivalves, fish and decapod crustaceans on the sandy shore at Starfish Bay, Hong Kong Britton and Morton, 1992. Its opportunistic
scavenging behaviour includes long distance food detection, fast locomotion towards it, and rapid consumption of an enormous amount relative to its body weight Morton,
1990; Britton and Morton, 1992.
In addition to nassariid gastropods, many other representatives of different phyla are scavengers of marine carrion, and intra- and interspecific competition can occur between
them Britton and Morton, 1993, 1994a. The feeding behaviours of other potential intertidal scavengers on sandy shores in Hong Kong and interactions, or competition,
between them, if any, have received less attention. On the soft shore at Shiu Hau, hermit crabs, including Clibanarius infraspinatus and Diogenes edwardsii, were considered to
constitute a scavenging force as important as nassariid gastropods Morton and Morton, 1983. Hermit crabs and Nassarius festivus were attracted to bivalve and soldier crab
Mictyris longicarpus baits put out on the shore at Starfish Bay, but the former were attracted in far fewer numbers than the latter Britton and Morton, 1992. Apart from
these observations, the scavenging behaviour of local hermit crabs, as well as their interactions with other scavengers, have not hitherto been studied.
Conversely, a number of studies on the scavenging behaviour of hermit crabs have been conducted elsewhere, but are confined to sublittoral species. Studies on the
behaviour of hermit crabs from Otago, New Zealand, demonstrated that 12 out of 15 species used scavenging as a subsidiary feeding mechanism and consumed all sorts of
carrion when available Schembri, 1982. Several studies have identified the hermit crab Pagurus bernhardus as one of the most important and abundant benthic scavengers that
aggregate in areas of fishing activity in the Irish Sea. Together with starfish, whelks, swimming crabs and fish, they feed upon fisheries discards which fall to the sea bed
Ramsay et al., 1997a,b, 1998. In addition, P
. bernhardus was shown to outcompete Pagurus prideauxi in areas of intense trawling activity Ramsay et al., 1996, 1998.
Intraspecific competition for food among P . bernhardus also exists and the number of
aggressive interactions and, hence, the intensity of competition increased with increasing
B . Morton, W.Y. Yuen J. Exp. Mar. Biol. Ecol. 246 2000 1 –29
3
numbers of individuals Ramsay et al., 1997a. Laboratory studies of P . bernhardus and
other epibenthic scavenging invertebrates collected from the Clyde Sea showed that the hermit crab was attracted to bait before the others Nickell and Moore, 1992a,b.
Confrontations in the form of short-term approach–retreat cycles were observed frequently among P
. bernhardus around the bait Nickell and Moore, 1992b. The counterparts of these crabs on intertidal sand flats in Hong Kong are Diogenes
edwardsii and Clibanarius infraspinatus, and both are common at Starfish Bay where they live sympatrically with Nassarius festivus. This study investigated and compared
their food preferences and their sequence of arrival at and departure from bait at this site. The more numerous D
. edwardsii was chosen for further investigations of feeding behaviour, in comparison with that of N
. festivus, in laboratory experiments. It was hypothesized that N
. festivus possesses certain characteristics which confer upon it an advantage in competition with D
. edwardsii for carrion, resulting in the dominance of the former over the latter in feeding clusters on the shore. Laboratory experiments
involving an investigation of the respective abilities of the two species to detect carrion and their consumption profiles were therefore carried out, and the results compared.
Finally, this study also aimed to provide evidence for interspecific competition. This is best studied by altering the densities of both species and monitoring their resource
utilization patterns Underwood, 1986; Begon et al., 1990. The ratio of the numbers of N
. festivus to D. edwardsii in feeding assemblages was manipulated, accordingly, and any changes in feeding patterns monitored.
2. Materials and methods
