Prolonged drought influences the taxonomic and functional structure of fish assemblages in estuaries along the Brazilian semiarid coast

We evaluated how fish assemblages in estuaries on the semiarid coast of Brazil are impacted taxonomically and functionally under two contrasting events: prolonged drought vs. ample precipitation. The fish fauna of six local estuaries was sampled, three under each event. The species composition of the two groups was compared using non-metric multidimensional scaling, permutational multivariate analysis of variance, and similarity percentages analysis. The functional structure was described using principal coordinate analysis and expressed as functional richness (FRic) and functional dispersion (FDis). We also ran extinction simulations to estimate how the most functionally original (FOri) and specialized (FSpe) species contributed to functional structure (FRic, FDis). Estuaries exposed to prolonged drought displayed greater abundance of marine stragglers and marine migrants and higher FRic values than did estuaries exposed to ample precipitation. They also suffered smaller losses in FRic when the most original and specialized species were removed. No clear pattern was discernible for FDis. In short, prolonged drought was associated with changes in the taxonomic and functional structure of the fish fauna in the sampled estuaries through the process of ‘marinization.’ Monitoring these ecosystems can predict changes in salinity associated with long-term global climate trends and their effects on the fish fauna.