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

Abstract

Identification, protection and enhancement of essential habitats are priority issues for management and restoration of exploited species. The shores utilized by Asian horseshoe crabs as nurseries were surveyed and the coastal habitat characteristics were described in the northern Beibu Gulf of China. Regression models were applied to explore species‐habitat relationships. Fourteen and ten nursery sites were identified for Tachypleus tridentatus and Carcinoscorpius rotundicauda populations, respectively. Xiacun and Jinhaiwan in the eastern region of the northern Beibu Gulf were the essential nurseries for T. tridentatus, whereas Shanxin and Jiaodong in the western part were the primary nursery shores for C. rotundicauda. These shores supported high densities (4–6 individuals/100 m2) of juvenile horseshoe crab populations. Mangrove and seagrass coverage area, coupled with sediment physico‐chemical parameters, particularly grain size, and the environmental heterogeneity of nursery habitats explained the distribution pattern of juvenile populations. Most juvenile populations were found along the outer fringe of mangroves in the small shallow estuary, particularly near outflows of tidal creeks with generally higher chlorophyll a and organic carbon contents. The distribution of high‐density juvenile populations of both species also overlapped with areas of seagrass patches. These findings highlight the importance of mangroves and seagrasses in the nursery habitat use of Asian horseshoe crabs. Preserving the estuarine habitats with these vegetation types and identifying the high‐use nursery sites should be prioritised in China and other Asian places to conserve the declining Asian horseshoe crab populations.

Ontogenetic resource use and trophic dynamics of endangered juvenile Tachypleus tridentatus among diversified nursery habitats in the northern Beibu Gulf, China

“…Rudloe (1981) observed a gradual offshore movement of juvenile L. polyphemus to the deeper waters as they age. However, no such movement pattern was observed for juvenile T. tridentatus either on Kinmen Island, Taiwan, China (Chen et al 2004) or in the northern Beibu Gulf, China (Xie et al 2020), possibly due to the flat topography of the shores. Adult horseshoe crab populations exhibited contrasting migration patterns throughout their range.…”

“…Larvae are transported to and forage on the adjacent sheltered beaches for 7 years or longer (Seino et al 2000;Cheng et al 2015). Nursery habitat for C. rotundicauda is associated with mangroves and mudflats (Xie et al 2020), while the juveniles of other 3 species are found on sandy-mudflats where meiofaunal and infaunal prey are abundantly found (Hsieh & Chen 2009;Cheng et al 2015). T. tridentatus and L. polyphemus molt approximately 16 times in 10-14 years, whereas, T. gigas and C. rotundicauda molt around 13 times in 10 years until adulthood is reached (Sekiguchi et al 1988;Walls et al 2002;Hu et al 2015).…”

“…The Beibu Gulf on the southern coast of China is widely considered as the most important habitat to harbor the remaining high-density T. tridentatus population globally (Brockmann & Smith 2009;Sekiguchi & Shuster 2009;Fu et al 2019;Liao et al 2019), given the peak annual average harvest rates in the Gulf ranged from 0.4-1.4 million individuals throughout the 1980s to serve bleeding and food consumption (Liang 1985;Liao & Li 2001). Xie et al (2020) identified 14 important nursery sites for T. tridentatus along the northern Beibu Gulf coast where the juveniles can be found in intertidal areas with varying habitat types: seagrass or Spartina patches, along the mangrove fringes, or on the bare sandy-mudflats. In this study, we examined (i) the trophic interactions of T. tridentatus with macrobenthic communities, (ii) potential ontogenetic differences in trophic niche width and trophic niche overlap between T. tridentatus age classes, and (iii) quantified the relative contributions of primary producers' carbon sources to juvenile T. tridentatus populations in diversified nursery habitats in the northern Beibu Gulf, China.…”

Habitat suitability maps for juvenile tri-spine horseshoe crabs in Japanese intertidal zones: A model approach using unmanned aerial vehicles and the Structure from Motion technique

“…This may be attributed to the lack of important factors explaining the habitat characteristics of the target species [ 59 ]. For example, biotic and abiotic factors, such as sediment condition, density of prey, and coverage of seagrass patches, affect the distribution of the juveniles [ 20 , 21 , 60 ]. The sediment condition, which is one of the factors affecting juvenile distribution, can be estimated with further development of the UAV-SfM technique [ 31 ].…”

Effects of Ocean Acidification on Molting, Oxidative Stress, and Gut Microbiota in Juvenile Horseshoe Crab Tachypleus tridentatus

“…The revised "List of key protected wild animals in China" in 2021 officially listed tri-spine horseshoe crab as the second-class national protected wild animal. Current studies on horseshoe crab mainly focus on population survey (Xie et al, 2019), resource conservation (Zhu et al, 2020), artificial breeding (Tinker-Kulberg et al, 2020), blood collection (John et al, 2011;Owings et al, 2019), and recombinant Tachyplesin (Yu et al, 2020). The impact of environmental factors on horseshoe crabs is mainly concentrated on heavy metals, salinity, temperature, and sediments (Kwan et al, 2015).…”