POPULATION GENETIC STRUCTURE OF JUVENILE CHINESE HORSESHOE CRABS IN HONG KONG

Populations of Chinese horseshoe crabs (Tachypleus tridentatus) are declining in Hong Kong primarily due to the destruction of spawning and nursery shores through coastal reclamation and increasing urban encroachment. Understanding their phylogeographic pattern is thus important to protect the remaining sites where juvenile horseshoe crabs are found. The genetic diversity of juvenile T. tridentatus was investigated by sequencing a mitochondrial gene region from 33 samples collected from six locations in Hong Kong. Eight haplotypes were identified, and the relationship among haplotypes was inferred using Network Analysis. Results indicated that T. tridentatus has a high level of endemism, and the population in Deep Bay is differentiated from that on the northwestern coast of Lantau Island. Horseshoe crabs at Shui Hau on the southern coast of Lantau Island are also geographically isolated. These genetic patterns may indicate the limited dispersal ability of Chinese horseshoe crabs in Hong Kong. A very low haplotype diversity observed on the northwestern coast of Lantau Island implies the problem of a population bottleneck, which may eventually result in local extirpation if an effective conservation plan is not put in place.