Conservation Program for the Asian Horseshoe Crab Tachypleus tridentatus in Taiwan: Characterizing the Microhabitat of Nursery Grounds and Restoring Spawning Grounds

Abstract

A study of the physical properties of horseshoe crab (Tachypleus tridentatus) nursery grounds indicated that juveniles preferred sediments consisting of fine sand with median grain size of 0.14–0.27 mm in diameter, 16.9–23.2% water content when tides receded, 0.23–0.41% TOC content, 0.04–0.07% TN content, 2.3–2.8 µg/cm2 chlorophyll a content, and poorly sorted substrates. Juvenile horseshoe crab density increased based on the amount of chlorophyll a content in the sediment and infaunal polychaete density, suggesting that the juveniles prefer nursery grounds containing abundant prey and its supporting food web. An effort to restore horseshoe crab spawning grounds was conducted by covering 20 cm deep mud substrate (0.23 mm in diameter) with coarse sand (1.10 mm in diameter). Although adults transferred to this site succeeded in laying eggs, the hatching rate was only 33.9%. This low rate may be attributed to small tidal amplitude at this restoration site.