Ecological filtering and functional trait patterns in polychaete communities of the Arabian Gulf.

Functional traits provide a mechanistic link between species attributes and ecosystem processes, offering insights into community responses to environmental gradients. This study examined how habitat heterogeneity structures macrobenthic polychaete functional diversity along the Saudi Arabian Gulf coast (Khafji to Ras Abu Qamis). Benthic habitats were classified into shallow, intermediate, and deep zones. Functional diversity indices-functional dispersion (FDis), functional richness (FRic), and Rao's quadratic entropy (RaoQ) were applied alongside RLQ and fourth-corner analyses to assess trait-environment relationships. Shallow and intermediate zones exhibited significantly higher functional diversity (p < 0.01), with traits such as small body size, infaunal position, burrowing mobility, and carnivory dominating. Deeper habitats showed reduced FRic and greater trait convergence, associated with fine sediments. Functional redundancy (FRed), over-redundancy (FORed), and vulnerability (FVuln) assessments revealed that most functional entities were supported by a single species, indicating low ecological buffering capacity. Variance Partitioning Analysis attributed significant portion of functional diversity variation to sediment properties, with grain size (Φ) identified as the primary driver. Structural Equation Modeling confirmed grain size as a significant negative predictor of FDis, FRic, and RaoQ. These findings underscore the role of sediment structure and depth-related environmental gradients in shaping the functional composition of polychaetes. The low redundancy observed highlights the vulnerability of Gulf benthic systems to biodiversity loss, reinforcing the need for sediment-focused conservation strategies.