Assessing tropical coastal dynamics across habitats and seasons through different dimensions of fish diversity.

Coastal habitat mosaics are among the most productive ecosystems around the globe, with many ecological and social-economic services provided. Their natural challenging conditions have always been a subject of concern for ecologist and conservationist, with a particular interest in understanding how its spatial and temporal dynamics influence ecosystem functioning. In this context, we aimed to assess tropical coastal dynamics using an integrative approach, measuring the different facets of fish diversity across space (habitats) and time (seasons). Three different estuarine systems and their adjacent areas in the southwestern Atlantic were monthly sampled between July 2017 and June 2018, in a sampling design that encompassed three different coastal mosaics with three habitat types (mangroves, seagrass and sandy beaches), and both seasons of the studied region (dry and rainy). Taxonomic, phylogenetic, and functional diversity were then evaluated with equivalent diversity measures to allow comparisons between them. Different patterns of species occurrence and distribution were found between habitats and seasons, which resulted in different effects on the abundance-weighted diversity dimensions. Although taxonomic diversity of habitats was greater during the rainy season (p = 0.03), a seasonal increase in phylogenetic diversity was only observed in the sandy beach habitat (p = 0.04). In contrast for the functional diversity, no significant differences were found among habitats in both seasons (p = 0.15), indicating high levels of redundancy. Our results showed that patterns in the occurrence and abundance of tropical fish species among habitats that comprise a coastal mosaic have different effects on distinct diversity dimensions. More precisely, for tropical coastal systems with marked seasonality, both habitats and season appear to play a synergic role in the maintenance of ecosystem functioning by enhancing functional and phylogenetic redundancy.
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