Multiple habitats drive the functional diversity of fish assemblages in a tropical estuary.

Understanding estuarine diversity patterns is crucial to highlight the ecological value of coastal ecosystems for fish assemblages. To increase our knowledge, we investigated the functional diversity of fish assemblages in five estuarine habitats (sandy beaches, mudflats, seagrass meadows, mangrove fringes, and estuarine riparian vegetation) in a tropical estuary of Brazil. Functional diversity metrics were assessed considering seven fish functional traits and calculated using functional indices, PCoA (functional spaces), and community-weighted mean (CWM). Then, a unified RLQ and fourth-corner analysis were used to evaluate environment-trait relationships. A total of 27,036 individuals of 119 species were recorded in all habitats. Functional diversity showed similar trends to estuarine habitats, which were more driven by the spatial configuration rather than by their structure, emphasizing the importance of environmental heterogeneity. There was a greater occupation of functional space to habitats located in the lower estuary compared to the upper estuary. Furthermore, body shapes and trophic guilds were the most common traits related to changes in functional diversity between habitats. The RLQ analysis revealed differences in trait composition between habitats influenced by salinity and transparency, although the fourth corner method did not show a significant relationship between fish functional traits and environmental variables. Our results suggest that the mosaic of habitats support the high functional diversity of fishes in tropical estuaries.

Does environmental heterogeneity explain ß diversity of estuarine fish assemblages? Example from a tropical estuary under the influence of a semiarid climate, Brazil.

Estuarine fish assemblages are often sensitive to environmental conditions, because fluctuation in physico-chemical conditions at different spatial and seasonal scales can directly influence species distributions. In this way, we conducted a field survey to investigate the role of estuarine gradient (environmental heterogeneity) in fish α and ß diversity. The study was carried out in three zones in Mamanguape River estuary according to salinity and geomorphology features during an atypical climatic event in 2015. In total, 18,084 specimens of 125 species were captured. Additive partitioning of diversity analysis detected a higher proportion of beta diversity among estuarine zones during the rainy (ß3 = 58.6%) and dry season (ß3 = 40.94%) and were higher than expected by chance (Propexp> obs <0.001). Decomposing ß-diversity analysis showed that total ß-diversity (ßsor) results were more dominated by species turnover (ßsim) than nestedness (ßnes) in both seasons. Forward selection procedure and db-RDA identified salinity, coarse sand and chlorophyll-a as the main environmental variables influencing ßsor and site distance from estuary mouth and split as the main landscape variables. Variation partitioning analysis revealed more contribution to the pure fraction of environmental variables to fish species turnover, however, both pure fraction of environmental and landscape variables significantly contributed to ßsim. Our study highlighted the importance to environmental heterogeneity and connectivity to promote fish diversity across the Mamanguape River estuary. Thus, future conservation policies should focus on maintaining these two components to guarantee its nursery ground role to estuarine fish assemblages.