Environmental factors influencing the community structure of shrimps and crabs (crustacea: Decapoda) in headwater streams of the Rio Jaú, Central Amazon, Brazil

Abstract

Longitudinal variations in physical-chemical characteristics of headwaters streams can have predictable effects on habitat and benthic community structure. The objective of this stud y was to investigate the influence of spatial variation in river channel characteristics and habitat structure on the abundance and community structure of shrimps and crabs in headwaters streams of Rio Jaú. Collections and measurements for the characterization of crustacean community structure, habitat structure and channel characteristics were made in 34 headwater streams during the period of November - December of 1998. Crustaceans were captured with traps and hand nets along standard two meander sample reaches. Data on benthic habitat structure and stream morphology were collected along ten equally spaced lateral transects. A total of nine species from three families were collected. Significant relationships were obtained between % sand and % leaf cover on stream bottoms and the number and biomass of shrimps and crabs, independent of stream size. Channel size explained a significant part of the variability in decapods community structure among streams. When streams are degraded and habitats are lost, many species restricted to those habitats may disappear and the trophic structure of crustacean communities could change.