Spatio-temporal variation in the density and diversity of decapods captured with artisanal traps in an Amazon estuary

Abstract

Aim: The variability in density and species diversity of decapod crustaceans was investigated on four islands with different degrees of anthropogenic disturbance around the city of Belém, State of Pará. Methods: Samples were obtained from 15 creeks using artisanal traps, every three months between October 2013 and May 2014 on Combu, Onças, Cotijuba and Mosqueiro islands. Results: Salinity and temperature little varied, which is common for a tropical Amazon estuary strongly influenced by freshwater inflow. A total of 8,367 decapods were captured, with one record of an exotic species Penaeus monodon. In all seasons, decapod density and richness tended to increase from Combu to Mosqueiro, with increasing proximity to the sea and higher salinity and pH. Except for Combu, species richness and Margalef diversity tended to be slightly greater in the wet season at all islands, especially Onças. Eveness and Shannon diversity did not vary greatly between seasons but were lowest at Onças in the dry season and highest at Combu, decreasing to Mosqueiro, in the wet season. In general, ecological indices are similar in the dry and transition dry to wet seasons, and in the wet season, dominance occurs at Mosqueiro Island. Macrobrachium acanthurus, C. bocourti and P. gracillis were associated with the wet season, whereas M. surinamicum prefers the dry season. M. amazonicum and Macrobrachium sp. have no well-defined seasonal pattern of occurrence at all the islands. Conclusions: Despite anthropogenic disturbances and proximity to large human populations, especially on Mosqueiro Island, the density and diversity of decapod crustaceans appear to be reasonably unaffected for the moment.