Habitat use of globally threatened juvenile Chinese horseshoe crab, Tachypleus tridentatus under the influence of simulated intertidal oyster culture structures in Hong Kong

Abstract

1.Little is known about the ecological impacts of oyster culture structures on intertidal communities. In the present study, distribution and movement patterns of juvenile Chinese horseshoe crab, Tachypleus tridentatus were assessed on a mudflat at Ha Pak Nai in Deep Bay, Hong Kong.2. As the traditional bottom-laying method of using concrete posts as cultch for collecting oyster spat is a common practice in Hong Kong, structurally similar bricks were used to simulate the potential effects of cultch on intertidal flats.3. Over the two-month experimental period, all the tested sediment physico-chemical characteristics, including median particle size and total organic content, remained unchanged among the treatment areas. However, juvenile densities and foraging trails at low-and high-density brick areas were significantly lower/shorter compared with the adjacent bare areas. Such effects were more evident for larger individuals since significant correlations were found between foraging distance and juvenile prosomal width in no-brick areas, but not the low-and high-density brick areas. In addition, most juveniles (> 95%) were observed feeding along the outer boundaries of brick areas.4. Such findings imply that the extensive artificial structures in oyster cultivation sites could induce physical disturbance and alter the habitat use of juvenile horseshoe crabs in the intertidal zone. Considering the high conservation value of Chinese horseshoe crabs, appropriate mitigation measures should be implemented to buffer the detrimental effects on horseshoe crabs and other marine organisms of conservation concern that utilize intertidal habitats as nursery and hatchery grounds.

Using Applied Statistics for Accurate Size Classification of the Endangered <i>Tachypleus tridentatus</i> Horseshoe Crab

“…We are certain that morphological sizing is a strategy adopted by horseshoe crabs after learning from their environment. Presently, T. gigas and C. rotundicauda are known to change spawning locations on the shore, constructs burrows with different depths and stocks the nest differently (28-303 eggs) in every season (Kwan et al, 2018(Kwan et al, , 2016Pati et al, 2020).The fisheries practices, residential inhabitancies and mangrove forest clearing over many generations in Kunak and Semporna (Harun et…”

Mangrove horseshoe crab (Carcinoscorpius rotundicaudaLatreille, 1802) populations reveal genetic break in Strait of Malacca, with connectivity along southern coasts of Peninsular Malaysia

“…As Kuala Sepetang falls under the riverine mangrove category (Goessens et al, 2014), more than 80% of the sediment is dominated by silt and clay (Ariffin & Mustafa, 2013) that is unfavourable for the nesting activity of C. rotundicauda . Moreover, the intertidal zones close to mangrove and seagrass beds were found to be important for foraging and the development of juvenile horseshoe crabs (Kwan, Chan & Cheung, 2017). Further scientific evidence, also through considering water current and circulation patterns in the Strait of Malacca, is therefore necessary to identify the local or regional movement of horseshoe crabs from their breeding ground(s) adjacent to Kuala Sepetang, and to confirm its status as a feeding ground.…”

“…As Kuala Sepetang falls under the riverine mangrove category (Goessens et al, 2014), more than 80% of the sediment is dominated by silt and clay (Ariffin & Mustafa, 2013) that is unfavourable for the nesting activity of C. rotundicauda. Moreover, the intertidal zones close to mangrove and seagrass beds were found to be important for foraging and the development of juvenile horseshoe crabs (Kwan, Chan & Cheung, 2017).…”

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

“…Researchers searched for the emerging individuals within each quadrat, followed by species identification. The juveniles do not feed at elevated ridges without a surface water layer during low tides (Kwan, Chan, & Cheung, ; Wong, ). Therefore, the dry area in each quadrat was not included in the search.…”