Ontogenetic changes in dietary carbon sources and trophic position of two co-occurring horseshoe crab species in southwestern China

Abstract

Understanding which food sources are nutritionally important at nursery grounds is critical in the conservation of the dwindling populations of horseshoe crabs in Asia. We used δ 13

Nursery habitat for Asian horseshoe crabs along the northern Beibu Gulf, China: Implications for conservation management under baseline gaps

“…Landscape‐level factors such as the area of coverage of mangrove forests and seagrass patches were positively correlated with juvenile densities, implying the high nursery value of these habitat types. Seagrass organic matter serves as food for the early‐instar horseshoe crabs, and supports the growth of other benthic invertebrates which, in turn, are the food of older juveniles (Fan et al, ; Kwan, Cheung, & Shin, ). Although dietary contribution of mangrove‐derived organic matter to both Asian horseshoe crab species is very low (<3%, Fan et al, ), intertidal areas with mangrove forest near high‐water line can serve as essential spawning habitats for C. rotundicauda (Fairuz‐Fozi et al, ).…”

“…Seagrass organic matter serves as food for the early‐instar horseshoe crabs, and supports the growth of other benthic invertebrates which, in turn, are the food of older juveniles (Fan et al, ; Kwan, Cheung, & Shin, ). Although dietary contribution of mangrove‐derived organic matter to both Asian horseshoe crab species is very low (<3%, Fan et al, ), intertidal areas with mangrove forest near high‐water line can serve as essential spawning habitats for C. rotundicauda (Fairuz‐Fozi et al, ). This finding is consistent with the results that sediment Chl a and/or TOC contents were, in general, higher at areas near mangrove and seagrass beds (Supplementary Material 3).…”

DNA Metabarcoding Revealed Interspecific Dietary Difference and Prey Selectivity in Juvenile Horseshoe Crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus From Hong Kong

“…Gut content examination on C. rotundicauda and T. tridentatus suggests that both species had a strong preference on consuming insect larvae (Zhou and Morton, 2004). However, subsequent studies on T. tridentatus juveniles from Hong Kong (Kwan et al, 2015) and C. rotundicauda and T. tridentatus from Pearl Bay in Guangxi (Fan et al, 2017) based on stable isotope analyses suggested that a mixed diet with seagrass contributed to most of the dietary carbon for both species, supplemented with polychaetes, crustaceans, and bivalves. Hence, the findings from various studies are inconsistent, even they were conducted in the same locality [e.g., Pak Nai, Hong Kong (Zhou and Morton, 2004;Kwan et al, 2015)].…”

“…The majority of researches on horseshoe crabs was focused on L. polyphemus, in particular the adults, whilst relatively limited information is known for the feeding habit of the three Asian horseshoe crab species (Luo et al, 2020). There are some studies on the diet of T. tridentatus and C. rotundicauda based on microscopic examinations of gut contents (Zhou and Morton, 2004;Pahang et al, 2012) and stable isotope analyses (Kwan et al, 2015;Fan et al, 2017), yet these studies revealed inconsistent or even contradictory observations and conclusions. Mollusks were most commonly reported food items of adult horseshoe crabs for both Atlantic and Indo-West Pacific species [e.g., L. polyphemus from North America (Botton, 1984;Botton and Ropes, 1989), T. gigas from India (Chatterji et al, 1992), and C. rotundicauda from Malaysia (Pahang et al, 2012)] based on gut content examinations, while polychaetes were also found to be dominant prey for C. rotundicauda from Singapore (Leng and Sivasothi, 2015).…”

“…Hence, the findings from various studies are inconsistent, even they were conducted in the same locality [e.g., Pak Nai, Hong Kong (Zhou and Morton, 2004;Kwan et al, 2015)]. Furthermore, gut content examinations (Zhou and Morton, 2004;Pahang et al, 2012) consistently suggested that C. rotundicauda and T. tridentatus are selective feeders, while the stable isotope study showed that the two species are dietary generalists (Kwan et al, 2015;Fan et al, 2017). It remains unclear whether the discrepancies in findings are caused by geographic and temporal variations, differential sensitivity of the adopted techniques and/or among different developmental stages to different food items.…”