The feeding behaviour and competition for carrion between two sympatric scavengers on a sandy shore in Hong Kong: the gastropod, Nassarius festivus (Powys) and the hermit

Field and laboratory experiments compared the feeding behaviours of two marine scavengers, the gastropod, Nassarius festivus and the hermit crab, Diogenes edwardsii, sympatric on the lower intertidal shore at Starfish Bay, Hong Kong. Field trials demonstrated that they both preferred bivalve and fish to other carrion. N. festivus arrived at bait in greater numbers and more quickly 3 than D. edwardsii. Numbers of the former species attracted to fish bait (1 cm ) peaked at a mean of 41 after 30 min, whereas the latter peaked at a mean of only 2.3 after 55 min. Laboratory investigations revealed that N. festivus was able to detect and move fast towards carrion from a distance of . 80 cm, feed quickly (x 5 13.20 min) and, after 14 days starvation, had a high 21 21 consumption rate (0.124 mg wet weight or 0.034 mg dry weight of food individual min , or 21 1.4% and 1.3% of its wet and dry body weights min , respectively). In contrast, D. edwardsii had a shorter food detection distance ( , 10 cm), took longer to arrive at bait, a variable feeding time ranging from 0.28 to . 119.75 min and a lower consumption rate (0.003 mg wet weight and 21 21 21 0.001 mg dry weight of food individual min , or 0.1% of its wet and dry body weights min , respectively). Manipulative experiments provided evidence for interspecific competition for carrion between the two species. A morphological advantage, i.e. an extendible proboscis allowing feeding at a distance, and chemoreceptors that permit long distance food detection, combined with numerical superiority on the shore, are mechanisms by which N. festivus outcompetes D. edwardsii and dominates feeding clusters. Interactive behaviour studies revealed the occurrence of interspecific interactions between the two species and intraspecific interactions among D. edwardsii but not N. festivus. The number of interspecific interactions fell when the numbers of N. festivus increased and those of D. edwardsii decreased, and vice versa. The aggressive D. edwardsii did not significantly affect the feeding behaviour of N. festivus. When the number of D. *Corresponding author. Tel.: 1 852-2809-2179; fax: 1 852-2809-2197. E-mail address: [email protected] (B. Morton) 0022-0981/00/$ – see front matter  2000 Elsevier Science B.V. All rights reserved. PI I : S0022-0981( 99 )00170-7 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.