The diets of juvenile horseshoe crabs, Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura), from nursery beaches proposed for conservation in Hong Kong

Abstract

Once common as a fishery resource, adult horseshoe crabs of two species occur in Hong Kong. A third, Tachypleus gigas, can no longer be found. Once common too were breeding and nursery beaches for horseshoe crabs in Hong Kong but overfishing of adults, pollution and coastal reclamation have reduced these to but three identified sandy mudflats and only one where juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda are sympatric. Nothing is known, however, of the conservation requirements of these two species locally and this study of the diets of these juvenile horseshoe crabs on two such nursery beaches aimed at providing information on this most elementary aspect of their biology. Gut contents of juvenile horseshoe crabs, i.e. nine Tachypleus tridentatus (8.5–67 mm prosoma width) and two Carcinoscorpius rotundicauda (50 and 52 mm prosoma width), were analysed and compared with the composition of the ambient assemblage of meiobenthos on a nursery beach at Pak Nai, Hong Kong. The obtained data suggest that juvenile horseshoe crabs of both species are selective benthic feeders and subsist mainly on insect larvae, polychaetes, oligochaetes, small crabs and thin-shelled bivalves. A strong, positive, preference for insect larvae (Chironomous sp.: Diptera: Chironomidae) was recorded, but with no preference for meiofauna over macrofauna.

Keywords:

• diet
• juvenile horseshoe crab
• Tachypleus tridentatus
• Carcinoscorpius rotundicauda
• nursery beach

Acknowledgements

This research was sponsored by a grant from China Light & Power Co. Ltd. We would like to thank the Board of Directors of the company and various members of its staff for logistical and other support during the course of the study.