The Behaviour of Juvenile Horseshoe Crabs, Tachypleus Tridentatus (Xiphosura), on a Nursery Beach at Shui Hau Wan, Hong Kong.

The aim of the present study was to examine some general aspects of feeding in Tachypleus tridentatus juveniles and the possible strategies employed to survive on sand flats experiencing a fluctuating environment, in terms of temperature, salinity and tidal action. Activity of Tachypleus tridentatus juveniles in the field was studied on each visit between September 1997 and June 1998, during low tides when the animals were crawling at the sand surface in the intertidal zone at Shui Hau, Lantau Island, Hong Kong. The patterns of feeding trails produced by the juveniles in the field and their crawling rates were determined and compared. Juveniles began to crawl on the sand surface after the tide had receded and the substratum exposed for about 1 h. The numbers of animals observed increased and peaked after a further 1 h. The number of active individuals gradually declined as most re-burrowed when the tide returned. Juveniles generally crawled in pool areas on the sand surface. A seasonal pattern was also evident in the number of juveniles observed at the study site. Highest numbers were recorded in summer whilst only a few juveniles were seen in winter. Possible strategies adopted by the juveniles for successful survival on the sand flats are discussed. [ABSTRACT FROM AUTHOR]