Visually Guided Behaviour of Juvenile Tri-spine Horseshoe Crab Tachypleus tridentatus: Implications for Designing Racks for Oyster Cultivation Compatible with Horseshoe Crab Conservation

Chan, Hoi Kin; Lo, Hoi-Shing; Ng, Siu-Kin; Chen, R. -F.; Cheung, S.G.

doi:10.1007/978-3-030-82315-3_12

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“…However, given that horseshoe crab populations are threatened and even endangered across the distribution range, previous studies suggest the use of artificially cultured horseshoe crabs is useful to explain the habitat selection mechanisms and distribution patterns of the wild populations ( e.g. , Medina & Tankersley, 2010 ; Hieb et al, 2015 ; Kwan et al, 2020 ; Chan et al, 2022 ). Apart from this, horseshoe crabs are also likely to use multiple sensory cues, particularly visual cues, in settlement habitat selection.…”

Section: Discussionmentioning

confidence: 99%

Chemically mediated rheotaxis of endangered tri-spine horseshoe crab: potential dispersing mechanism to vegetated nursery habitats along the coast

Kwan

Yang

Wang

et al. 2022

PeerJ

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Background An enhanced understanding of larval ecology is fundamental to improve the management of locally depleted horseshoe crab populations in Asia. Recent studies in the northern Beibu Gulf, China demonstrated that nesting sites of Asian horseshoe crabs are typically close to their nursery beaches with high-density juveniles distributed around mangrove, seagrass and other structured habitats. Methods A laboratory Y-maze chamber was used to test whether the dispersal of early-stage juvenile tri-spine horseshoe crab Tachypleus tridentatus is facilitated by chemical cues to approach suitable nursery habitats. The juvenile orientation to either side of the chamber containing controlled seawater or another with various vegetation cues, as well as their movement time, the largest distance and displacement were recorded. Results The juveniles preferred to orient toward seagrass Halophila beccarii cues when the concentration reached 0.5 g l−1, but ceased at 2 g l−1. The results can be interpreted as a shelter-seeking process to get closer to the preferred settlement habitats. However, the juveniles exhibited avoidance behaviors in the presence of mangrove Avicennia marina and invasive saltmarsh cordgrass Spartina alterniflora at 2 g l−1. The juveniles also spent less time moving in the presence of the A. marina cue, as well as reduced displacement in water containing the S. alterniflora cue at 1 and 2 g l−1. These results may explain the absence of juvenile T. tridentatus within densely vegetated areas, which have generally higher organic matter and hydrogen sulfide. Conclusion Early-stage juvenile T. tridentatus are capable of detecting and responding to habitat chemical cues, which can help guide them to high-quality settlement habitats. Preserving and restoring seagrass beds in the intertidal areas should be prioritized when formulating habitat conservation and management initiatives for the declining horseshoe crab populations.

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