Functional stability despite anthropogenic influences on the ichthyofauna of a tropical bay

Classifying species into groups based on taxonomic relationship and functions are objective approaches to evaluate environmental and anthropogenic influences on coastal fishes. We evaluated temporal (1993–1995 and 2012–2015) changes in the taxonomic and functional indices in three zones of a tropical bay heavily impacted over the recent decades. We tested the hypothesis that both indices decrease over time as result of the environmental degradation. A decrease in the taxonomic richness and abundance was observed mainly of the inner zone. The functional structure remained relatively stable, but the functional originality decreased significantly between the two periods. This functional loss is of particular concern because the loss of species with unique treats may generate a series of ecosystem damage. This information tells us that the use of functional indices is essential to complement taxonomic assessments and to detect a more detailed understanding of the real dimension of biodiversity loss in impacted environments. •The use of functional indices is essential to complement taxonomic assessments on biodiversity.•Temporal and spatial changes in the ichthyofauna in a tropical bay were found.•A decrease in the fish taxonomic richness and abundance was observed over time.•The functional originality decreased significantly over time.•The loss of species with unique treats may generate a series of ecosystem damage.