Assembly rules and functional groups at global biogeographical scales

1. The taxonomic and functional composition of reef fish assemblages are quantified in three biogeographical regions: Great Barrier Reef, French Polynesia and Caribbean. Assemblages are described in three habitats of differing wave exposure. Functional abilities are estimated based on published analyses linking fin morphology and swimming performance. 2. Two questions were addressed: (1) To what extent are labrid assemblages similar among habitats and regions? (2) To what extent are functional characteristics of fish assemblages shaped by differences in biodiversity, evolutionary history and species composition? 3. All three regions display highly congruent patterns of habitat use, in terms of assemblage structure and functional characteristics, despite a five-fold difference in species richness, limited or no species overlap, and a 3·2-Myear history of isolation. Exposed reef crest assemblages were dominated by fishes with fins reflecting lift-based highspeed locomotion. In contrast to abundance-based patterns, species presence/absence data were uninformative. 4. The relationship between swimming ability and habitat use reveals underlying assembly rules at a functional level, emphasizing the utility of functional attributes as a metric for comparing system-level properties in taxonomically distinct faunas.