Comparison of the Macrozoobenthic Community and Sedimentary Environment with and Without Horseshoe Crab Presence in the Crocodile Island Intertidal Zone, Xiamen, China

In order to compare the macrozoobenthic community and sedimentary environment with and without the presence of horseshoe crabs, the benthic macrofauna, sediment grain size, chromium (Cr), cobalt (Co), nickel (Ni), polycyclic aromatic hydrocarbon (PAHs), organic carbon and nitrogen were seasonally investigated at site A (with horseshoe crab presence), sites B and C (without horseshoe crab presence) in the Crocodile Island intertidal zone in Xiamen from June 2018 to July 2019. The results showed that most of the community parameters of benthic macrofauna, population parameters of common benthic macrofauna and environmental parameters were significantly different at the sites with horseshoe crab versus non-horseshoe crab sites. A two-way ANOVA test showed that the densities of Ceratonereis erythraeensis and Sigambra hanaokai had significant site variation. Cluster and non-metric multi-dimensional scaling (NMDS) analysis showed the community composition of benthic macrofauna was significantly different among the three sampling sites over four seasons. The mean sand content at site A (64.32%) was higher than those at site B (36.01%) and site C (18.86%). Conversely, the mean contents of silt, clay, Cr, Co, Ni, organic carbon, organic nitrogen, phenanthrene, and pyrene at site A were lower than those at site B and site C. These observations are consistent with the expected preferences of horseshoe crabs to live in areas with 60% sand content, which is associated with abundant and edible clamworms in the Crocodile Island intertidal zone, Xiamen.