Spatial organisation and functional composition of benthic reef assemblages across a depth gradient in western Aldabra Atoll

Introduction Coral reefs face unprecedented structural reorganisation following climate-induced mass mortality. While net coral loss is well-documented, the resulting spatial arrangement of surviving communities remains understudied. This study characterises the spatial organisation, functional composition, and environmental drivers of benthic communities on the western seaward reefs of Aldabra Atoll, Seychelles, using data from 2022. Methods Using 300, high-resolution 1 m 2 video-still quadrats across two depth contours (8 m and 15 m), we integrated genus-level identification with life-history strategies (LHS) and substrate stability analysis. Results Our data revealed that the reefs were overwhelmingly dominated by stress-tolerant, massive corals, reflecting a resilient, post-disturbance state following historical thermal anomalies. However, multivariate dispersion (patchiness) significantly increased with depth highlighting the role of environmental filtering. We identified four spatial organisational “signatures” among organisms and abiotic features. Using the Variance-to-Mean Ratio (VMR), we identified a deterministic shift in spatial signatures: from shallow aggregated frameworks to deeper, fragmented nucleated patches. Statistical niche modelling confirmed that substrate stability acts as a physical bottleneck; Isopora spp. exhibited an extreme affinity for rock pavement, while Goniopora spp. dominated mobile rubble. Discussion Our results demonstrate that post-bleaching recovery in Aldabra is partly driven by niche-driven environmental filtering rather than purely stochastic neutral drift.