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.

Hierarchical partitioning of fish diversity and scale-dependent environmental effects in tropical coastal ecosystems.

The spatial structure of the fish diversity and site-scale and landscape-scale environmental effects were investigated across hierarchical levels in tropical coastal ecosystems. Total diversity (γ) was hierarchically partitioned into α and ß components using both the additive and multiplicative methods. A model selection based on the AICc was applied to generalized linear mixed models relating diversity measures to environmental variables and including random effects for hierarchical levels and season. Short-term seasonal effects were negligible. Spatial effects were more relevant at the site level and negligible at the subregion level, due to the high spatial heterogeneity and the natural pooling of ecosystems, respectively. Site-scale environmental effects were more relevant at the subregion level, with eutrophic conditions (continental influence) favoring the species richness (α and γ) and higher absence of species (ßA) in oligotrophic conditions (marine influence). At the system level, the positive effect of the distance from the ocean on γ and higher ßA in oligotrophic conditions reinforced the positive continental influence on fish diversity. Environmental homogenization processes were most likely associated with the negative effect of the pasture cover on α at the system level, and γ and ßA at the site level. The negative effect of the forest cover on the later diversity measure evidenced its relevance to maintain richer but more similar assemblages, whereas the positive continental influence was most likely due to the loss of stenohaline marine species. This study evidenced that disentangling spatial, land use, and marine vs. continental effects on diversity components is critical to understand the primary determinants of the fish diversity in tropical coastal ecosystems.