AQUATIC BIOLOGY Aquat Biol Vol. 7: 107–112, 2009 doi: 10.3354/ab00194 Printed November 2009 Published online October 22, 2009 INTRODUCTION Horseshoe crab is the common name of 4 species of marine arthropods (Xiphosura, Chelicerata) found on the east coasts of Asia and North America. Despite their name, these animals are not crabs at all, but are related to scorpions, spiders and extinct trilobites. Tachypleus tridentatus (Leach 1819), known as the Japanese or Chinese horseshoe crab, is a species in the family Tachypleinae. Tachypleus tridentatus larvae tend to stay in their nests immediately after hatching, where they usually reside over winter. They then leave the nests and live at or near their natal beaches throughout the next spring or summer (Sekiguchi 1988). Juvenile T. triden- tatus bury themselves in the sand/mud sediment dur- ing high tide and emerge on the sediment surface to feed during low tide (Chen et al. 2004, Chiu & Morton 2004); therefore, they can be found at the sediment surface or buried in sediments in their nursery inter- tidal zone (Rudloe 1979). Adult T. tridentatus spend the winter in hibernation on the offshore ocean bottom at depths of 20 m, and then migrate from their winter deeper-water habitat to the shallow areas of coves when seawater temperatures rise in the summer (Seki- guchi 1988). The life-history characteristics and habitat preferences of the Chinese horseshoe crab suggest that the dispersal capability of juveniles might be restricted, resulting in substantial population subdivi- sions on a small geographic scale (Pierce et al. 2000, King et al. 2005). Populations of Tachypleus tridentatus in Asia have declined sharply for the past several decades. In Japan, T. tridentatus has been designated as a protected spe- cies since 1928 owing to near extinction, but its popula- tion size remains under threat (Botton et al. 1996). Hong Kong populations have shown similar trends, with de- clines in juvenile densities found on nursery beaches in © Inter-Research 2009 · www.int-res.com *Corresponding author. Email: bhpshin@cityu.edu.hk Summer distribution and abundance of juvenile Chinese horseshoe crabs Tachypleus tridentatus along an intertidal zone in southern China Menghong Hu 1 , Youji Wang 1 , Yan Chen 1 , Siu-Gin Cheung 1 , Paul K. S. Shin 1, *, Qiongzhen Li 2 1 Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, SAR 2 Guangxi Institute of Fisheries, Nanning, Guangxi, 530021, PR China ABSTRACT: Owing to human exploitation, pollution and loss of breeding and nursery grounds, Chinese horseshoe crabs Tachypleus tridentatus are facing the risk of population decline and even- tual extinction. In order to provide baseline information needed to formulate future conservation strategies, we examined the spatial distribution, densities and carapace width of juvenile T. tridenta- tus along 6 transects at an intertidal zone of Beibu Gulf, South China Sea, during the summer of 2008. The environmental parameters measured (water temperature, salinity and dissolved oxygen) did not vary significantly among transects. However, the abundance and size distribution of juvenile T. tri- dentatus was statistically different between transects. Juvenile T. tridentatus prefer to move further from their natal area as they grow: therefore, smaller juveniles tend to be distributed closer to the shore, while larger juveniles are located further offshore. KEY WORDS: Chinese horseshoe crab · Tachypleus tridentatus · Distribution · Abundance · Size variation · Intertidal zone · Beibu Gulf Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS