Ecological uniqueness of fish assemblages in tropical estuarine and coastal systems: Assessing environmental and spatial drivers

We assessed the local and species contributions to beta diversity, as well as its relationships with environmental and spatial drivers along the eastern Brazilian coast. Using abundance-based indices, total beta diversity was partitioned into "Local Contribution to Beta Diversity" (LCBD) and "Species Contribution to Beta Diversity" (SCBD) components at two levels (estuarine-coastal systems; estuarine and coastal areas). Furthermore, we evaluated the relationships between LCBD values and local environmental conditions and spatial structures, in addition to fish assemblage metrics. Our results indicated that LCBD values were higher in the estuarine areas compared to their adjacent coastal areas and primarily associated with lower salinity and depth, and higher temperatures. Spatial effects were indicative of higher local uniqueness related to unmeasured large-scale processes. Sites with higher species diversity and lower dominance had higher LCBD, while species richness had slight positive influence on LCBD at both levels. The contributions of species varied within and between levels, but the highest SCBD values were supported primarily by common and dominant species. Our study highlights the importance of the environmental conditions provided by estuarine areas for the overall variation of fish assemblages.