Better with more or less salt? The association of fish assemblages in coastal lagoons with different salinity ranges

Coastal lagoons are naturally stressed systems and experience changes in environmental conditions because freshwater inputs change environmental variables, mainly the salinity. We hypothesized that fish assemblages would change in structure and richness in three tropical lagoons that had different salinity ranges (a hyperhaline lagoon, 36-54; a euhaline lagoon, 16-40; and a mesohaline lagoon, 8-34). The assemblage structure differed among the three lagoons, and changed seasonally only in the mesohaline lagoon with the biomass being comparatively higher in summer than that in winter. The four environmental variables (salinity, temperature, turbidity and depth) explained a significant proportion of the variance, with salinity having the most significant effect (approximate to 10% of the explained variation) on fish assemblage structure. The mesohaline lagoon, with the widest salinity range (from estuarine to marine conditions) and more loads of nutrient brought by small rivers' inflows, was the most abundant (in fish number and biomass) system. The euhaline lagoon, with a salinity range closest to marine conditions, had the highest species richness as opposed to the hyperhaline lagoon that appeared to limit species abundance and richness, probably due to the stress of high salinity.