The occurrence of fish species in multiple habitat types in a tropical estuary: Environmental drivers and the importance of connectivity

The presence of multiple habitat types results in differences in provision types and functions for a number of fish species along tropical estuaries, which use these ecosystems as nursery, feeding, and reproduction grounds. We compared fish assemblages along three habitat types (beaches, mudflats and mangrove fringes) in a tropical estuary using samples collected during rainy and dry seasons. A total of 11,260 individuals belonging to 31 families and 93 species were collected. The abundance and biomass of fishes declined from mudflats and mangrove fringes to beaches, with the highest values occurring in the dry season. Species richness showed the same tendency. Temporal trends were found among habitats during this study. Overall, 56 fish species were recorded in at least two habitats, and only 19 species were recorded in all three habitats; the number of species recorded only in mangrove fringes was higher than in other habitats. The fish composition between mudflats and mangrove fringes was more similar, indicating that connectivity plays an obvious and crucial role in the movements of fishes between them. A combination of four (salinity, coarse sand, clay, and organic matter) and three (salinity, coarse sand, and organic matter) environmental predictors accounted for 94.8% of the variation in abundance and 94.7% of the variation in biomass in the fish community structure among estuarine habitats. The multiple habitat types in this tropical estuary maximize opportunities for the survival and growth of numerous fish species. Specifically, we show that there was high similarity in species composition among hab-itats, which reinforces the hypothesis that most juvenile fishes do not necessarily move from one shallow habitat to another, but simply occupy shallow estuarine waters regardless of habitat type.