A dual stable isotope study for diet composition of juvenile Chinese horseshoe crab Tachypleus tridentatus (Xiphosura) on a seagrass-covered intertidal mudflat

Abstract

To enhance our understanding on the foraging biology of juvenile Chinese horseshoe crab on a seagrass-covered intertidal mudflat, we used dual stable isotopes δ13C and δ15N to determine the diet composition and trophic position of 6th–11th instar juveniles in summer and winter. The δ13C and δ15N values in tissues of juveniles and their potential food sources suggested that the juveniles consumed a mixed diet mainly comprised a variety of polychaetes, crustaceans and bivalves, in which these food groups were abundantly available in the study site and largely supported by seagrass biomass in both summer and winter. While δ15N values in juvenile tissues were statistically similar between the two seasons, the δ13C values in tissues of juveniles had a minimal seasonal difference which was probably due to variations in the source values rather than the changes in diet composition of juveniles. There were no differences in δ13C and δ15N values among the size groups of juveniles through 6th–11th instars. Although juvenile Chinese horseshoe crabs may consume the prey in response to the seasonal availability on the mudflat, a healthy condition of habitat with high water quality is essential to support the juveniles and a wide range of intertidal invertebrates they consume.