Functional and Taxonomic Overlap in Shore Fish Assemblages in a Tropical Seascape

The relationships between shore fish assemblages from habitats neighboring coral reefs have received little attention in the Indo-Pacific. The present study is based on the extensive sampling (539,000 fish: 898 taxa) of three fish assemblages: reefs, mangroves, and soft-bottoms in a large bay of New Caledonia. Species area curves indicate that sampling was nearly exhaustive in all three habitats (262 species in mangroves, 342 on soft-bottoms, 594 on reefs). Combinations of life-history traits were used as proxies of ecological functions. The species and functional overlaps were highest between soft-bottoms and mangroves and lowest between mangroves and reefs. These overlaps were lower than most recent studies in the Indo-Pacific, a result probably linked to the extent of the sampling in the present study. The life-history traits of species found exclusively in one habitat as opposed to several habitats were not a random selection within the species pool. Overlapping species were mostly large species that fed on nekton, large invertebrates, or plankton: exclusive species were mostly sedentary, solitary, and of small size, except for plankton-feeding species, which mostly had large home ranges and formed large schools. Herbivores were seldom found in several habitats. Functional redundancy was correlated to species richness, and was highest in reef fish assemblages. Functions common to several habitats had very seldom the same relative redundancy, implying that these functions had not the same importance for each assemblage. Functions exclusive to one habitat generally had low redundancy. These functional attributes and species overlap suggest that these three assemblages have a low level of interaction, despite the fact that they share extensive boundaries. These findings may have important applications in the management of shore fish assemblages.