Abstract
Aim To investigate how functional traits shape the composition and functional structure of coastal fish assemblages across the four North‐East Atlantic archipelagos, providing insights into the ecological drivers of species distributions and trait patterns in oceanic island systems. Location Four North‐East Atlantic oceanic archipelagos within Macaronesia: the Azores, Madeira, Canary Islands and Cabo Verde. Taxon Coastal marine fishes occurring up to 200 m depth, comprising 682 species. Methods We compiled a validated checklist of coastal fish species (≤ 200 m depth) for each archipelago and integrated these data with a functional trait matrix comprising size category, trophic category, habitat affinity, milieu and climatic affinity. Generalised Linear Models (GLMs) were used to assess the influence of traits on species occurrences. Functional community structure was quantified using six functional diversity indices: functional richness (FRic), evenness (FEve), divergence (FDiv), dispersion (FDis), Rao's quadratic entropy (RaoQ) and FRic intersection (FRic Inter). Model performance was evaluated using AIC, BIC, pseudo R 2 and post hoc comparisons. Trait‐based GLMs were complemented with assemblage‐level RLQ ordination and fourth‐corner tests to evaluate trait–environment coupling while accounting for species co‐occurrence. Results Species richness followed a clear latitudinal gradient, peaking in the Canary Islands and declining towards higher latitudes. RLQ revealed strong global trait–environment co‐structure (Axis 1 = 91.7% of projected inertia), whereas Fourth‐Corner tests detected no individually significant trait–environment associations after Holm correction. RV tests indicated a significant link between trait structure and species composition (Q–L), but not between environmental context and species composition (R–L). Among traits, body size and habitat affinity were the strongest predictors of species occurrences, with larger‐bodied and reef‐associated species more frequent in the southern archipelagos. Functional richness was highest in the Azores, indicating functional distinctiveness despite comparatively low species richness. Incorporating functional diversity indices into GLMs did not improve explanatory power beyond species‐level traits. Main Conclusions Body size and habitat affinity are key determinants of coastal fish assemblages across the Macaronesia archipelagos. Functional diversity peaks in the Azores, while Madeira exhibits intermediate trait compositions between temperate and tropical systems. These patterns provide insight into community assembly mechanisms and may inform predictions of species turnover under future climate change scenarios.