Composition of functional ecological guilds of the fish fauna of the internal sector of the Amazon Estuary, Para, Brazil

The present study describes the spatial and temporal structure of the estuarine fish community in the internal sector of the Amazon Estuary. Samples were obtained in the main channels and tidal creeks of Guajara and Marajo Bays and Guama River. A total of 41,516 fish specimens were collected, representing 136 taxa, 38 families and 12 orders. In the dry season, the mean salinity of the main channel increased along a limnic-marine gradient, between the Guama River and the Marajo Bay. Species richness was lowest in the mouth of the Guama River and in the right margin of the Guajara Bay. Fish species composition and environmental guilds differed markedly among areas: Migrants and Freshwater Stragglers were dominant in the Guama River and the Guajara Bay, while Estuarine, Marine Stragglers and Migrants predominated in the Marajo Bay. However, the trophic guilds were still relatively well balanced, in functional terms. Piscivores and Zoobenthivores were the dominant feeding functional groups in all the studied areas. In this study, the assessment of the community and the use of the guild approach were efficient to describe the structure and functioning of the assemblages of estuarine fish also helping to assess the anthropogenic pressures in the area.