Estuarine ecocline function and essential habitats for fish larvae in tropical South Western Atlantic estuaries.

Estuarine gradients rule the dispersal of larval fishes leading to community replenishment and the recruitment of juveniles to adult populations. Here, the variations in density and diversity of fish larvae communities were assessed to understand whether the seasonal variability of environmental forcings in two tropical estuaries express the estuarine function for larvae. Spatial differences ruled larval dispersal. Larval recruitment to the Caeté Estuary occurs in the upper estuary in the late-dry season. Species richness is higher when temperature, salinity and precipitation increase, while changes in diversity is more pronounced in the lower estuary due to salinity variability. Larval recruitment to the Goiana Estuary occurs in the lower estuary, with peaks during wet warmer conditions. Species richness and diversity are also higher seawards. Thus, the seasonal fluctuation of the salinity ecocline had a greater power to predict larvae distribution and diversity by retaining larvae in essential habitats with suitable environmental conditions.