AB prepress abstract  -  doi: 10.3354/ab00670

Species and life stage-specific changes in the carbon sources of horseshoe crabs Tachypleus tridentatus and Carcinoscorpius rotundicauda co-occurring in southern China

Lan-Feng Fan, Chang-Po Chen, Ming-Che Yang, Guanglong Qiu, Yong-Yan Liao, Hwey-Lian Hsieh*

*Email: zohl@gate.sinica.edu.tw

ABSTRACT: Understanding nutritionally important food sources at nursery grounds is vital to conserving the dwindling populations of Asian horseshoe crabs. We used δ13C and δ15N values to define life-stage changes in carbon sources assimilated by 2 co-occurring horseshoe crab species, Tachypleus tridentatus and Carcinoscorpius rotundicauda in a mangrove- and seagrass-vegetated estuary, Pearl Bay, in Guangxi, China. δ13C signatures in tissues of T. tridentatus and C. rotundicauda varied between species and among life stages within species, with the greatest differences occurring among younger life stages (instars 5–7; 20–30 mm). Life-stage specific diets were consistent with known habitat use by the 2 horseshoe crab species, with T. tridentatus reflecting slightly enriched seagrass carbon sources and C. rotundicauda reflecting influences of lighter sediment POM (–15.1 vs. ~ –15.8‰). Overall, seagrass was estimated to make the greatest contribution to dietary carbon of both species (~60%), followed by sediment POM (35%). δ15N signatures were similar between species (~11.6‰), with adult C. rotundicauda exhibiting a slightly more enriched signal than their juveniles (12.7 vs. 11.6‰), and all horseshoe crabs occupied secondary consumer trophic levels. The δ15N signatures in horseshoe crabs at Pearl Bay were lighter than those from more urbanized waters, potentially due to lower anthropogenic nitrogen loading. Our data suggest that effective international and national strategies for conserving threatened Asian horseshoe crabs would benefit from incorporating efforts to protect seagrass and mangrove habitats.