Abstract:

Aim: The juvenile Tachypleus tridentatus is an endangered marine arthropod whose juveniles, generally ranging from instars 1 to 12, inhabit intertidal sand-mud flats. This study aimed to assess the population status of juvenile Tachypleus tridentatus and characterize the habitat conditions of its nursery grounds in Dongshan Bay, Fujian, China. 

Methods: Surveys on the distribution of juvenile populations and nursery grounds were conducted along the coastal tidal flats of Dongshan Bay. Ten seasonal surveys were carried out at Shanqian Beach, Lieyu Town, from August 2021 to June 2025. Intertidal transect surveys combined with kernel density estimation were used to analyze the spatial distribution of juveniles. Sediment grain-size composition and macrobenthic community characteristics were compared among zones with different juvenile densities. 

Results: Shanqian Beach was the only remaining functional nursery ground identified in Dongshan Bay. Juvenile density ranged from 0.0096 to 0.1536 ind./100 m², indicating an overall low population density. Juveniles ranged from instar 3 to instar 12, with instars 6–9 accounting for a relatively large proportion of the population across survey years, indicating temporal variation in instar structure. Sediment grain-size composition differed significantly among density zones; high-density zones were characterized by sandy substrates with low gravel content and relatively higher silt content. The Shannon-Wiener diversity index, Margalef richness index, and Pielou evenness index of macrobenthos were significantly higher in high- and medium-density zones than in the low-density zones, whereas macrobenthic density and biomass did not differ significantly among zones. Macrobenthic community composition differed significantly among density zones, but this differentiation was primarily driven by variations in the abundance of a few dominant species, such as Simplisetia erythraeensis and Batillaria cumingi. 

Conclusion: The spatial distribution of juvenile T. tridentatus was related to sediment characteristics and macrobenthic community composition. We recommend prioritizing the protection of the core nursery zone in the northern part of Shanqian Beach, controlling anthropogenic disturbances, conducting comprehensive assessments of the nursery ground and its surrounding environment, and implementing scientifically guided stock enhancement and release to promote long-term population recovery. This study provides a scientific basis for the conservation and ecological restoration of nursery habitats of the Chinese horseshoe crab.

Key words: Dongshan Bay, Tachypleus tridentatus, juvenile Tachypleus tridentatus population, nursery habitat, sediment grain size, macrobenthos