Longitudinal variation and effects of habitat on biodiversity of Australasian temperate reef fishes

Abstract

Aim Latitudinal gradients in marine biodiversity of fishes are well documented but comparatively little is known about longitudinal patterns. The objective of this study was to describe the distributional patterns in biodiversity and assemblage structure of temperate reef-associated fishes in two habitats (kelp forests and open reefs) in each of four regions at comparable latitudes spanning a large longitudinal range (> 5000 km; 117.91° E–174.81° E). Location New Zealand, New South Wales, South Australia and Western Australia. Methods Total abundance, species richness, evenness, average taxonomic distinctness and variation in taxonomic distinctness were calculated from underwater visual counts of individual fish species and were analysed using ANOVA. Compositional change in fish communities was analysed using PERMANOVA and non-metric multi-dimensional scaling at the species level and at the family level. Results Patterns in univariate diversity measures did not show a clear longitudinal gradient and depended on the particular variable being considered. There was, however, a clear longitudinal gradient of turnover in species composition but this disappeared in family-level analyses. The effects of habitat were also relatively stronger in family-level analyses. Main conclusions We propose that ecological communities in similar habitats may be assembled according to a general ‘village hypothesis’, whereby an assemblage contains certain essential functional components. Regions having similar environmental characteristics are expected to have a full suite of these functional components. Thus, provided families reflect functional forms, this may explain the similarity among communities from vastly different regions when analysed at the family level. In contrast, the radiation of species within families may be regionally specific, depending on the history of oceanographic connectivity, microclimate and finer niche specialization, thus yielding strong regional differences in composition at this finer taxonomic level.