The goals of the present study were: 1) to test whether the shallow water ichthyofaunal diversity in the Formoso river (Pernambuco) varies between the upper and lower estuarine zones and between the dry and rainy season; and 2) to assess spatial and temporal shifts in their trophic categories. The fishes were collected bimonthly using beach seine. A total of 5,475 individuals were analyzed, belonging to 78 species, of which 51.3% were of reef origin. Carangidae and Gerreidae had the highest diversity, whereas Clupeidae, Engraulidae and Gerreidae were the most abundant. Among the dominant species (89%), Rhinosardinia amazonica was particularly common (36%). Most of the species were predators (75%), including species with carnivorous feeding habits of the 2nd order (37.5%). The only statistically significant difference in diversity occurred between the lower and upper estuarine zones, being higher in the former. This is probably due to the higher morphological complexity, to the larger proportion of Rhizophora mangle (shelter and refuge for several fishes), and to the mud sediment that makes this a more productive area. The Trophic Contribution Factor (FCT) for the debris was higher in the upper estuarine zone, where there is a higher rate of silt and clay. This TCF for primary production was higher in the middle estuarine zone, where there is higher phytoplankton biomass. Most species were in the young ecophase, corroborating the importance of shallow waters in this tropical estuary as a natural nursery and shelter for several fish of ecological and economical importance.
Ichtyophauna; feeding; mangroves; Pernambuco
