Depth and substrate shape the ecology of pen-shell Atrina vexillum in coral reef lagoons
摘要
Understanding how environmental gradients shape species distributions is essential for managing coral reef lagoons, where habitat heterogeneity drives benthic biodiversity. This study aims to establish the ecological baseline for the pen shell Atrina vexillum in the Society Archipelago (French Polynesia) by identifying the environmental factors structuring its distribution, size variation, and habitat use. Specifically, we tested whether depth and substrate jointly influence occurrence and shell size, and whether settlement patterns deviate from habitat availability across islands. Using stratified underwater surveys, we recorded over 2600 individuals and measured shell width, depth, and substrate type. Habitat-use analyses revealed non-random settlement patterns: coral substrates were consistently under-used relative to availability, while sand and muddy-sand were more used, sometime mixed with branching corals, with significant island-specific deviations from availability (χ2 tests, p < 0.001). Shell width showed a weak positive association with depth (ρ = 0.26, p < 0.001), an effect mainly driven by Bora-Bora where a pronounced depth gradient was sampled; other islands showed limited or no detectable depth-related size differences. Although abundance varied by more than an order of magnitude among islands, size distributions were mostly unimodal, a pattern consistent with continuous recruitment, but without clear evidence of recent, distinct cohorts. These findings identify A. vexillum as a key component of soft-bottom communities when they occur in numbers whose distribution and morphology are shaped by geomorphology. Recognizing its role as a sediment-stabilizing, filter-feeding ecosystem engineer can inform lagoon zoning and conservation strategies aimed at sustaining benthic functions and resilience in Polynesian reef ecosystems.