Effects of flow fluctuations on the daily and seasonal drift of invertebrates in a tropical river

¹ Laboratório de Ecologia de Bentos, Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, CP. 486, Pampulha, CEP 30161-970 Belo Horizonte, MG, Brazil
² Amnis Opes Institute and Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA

^* Corresponding author: diegobioufla@gmail.com

Received: 27 November 2012
Accepted: 15 May 2013

Abstract

Invertebrate drift results from several factors, including accidental dislodgement from the substratum, interaction with other invertebrates and predators, and changes in water quality, discharge and current velocity. We evaluated the degree to which flow fluctuations from dam releases altered the daily and seasonal invertebrate drift patterns in a tropical river. We collected macroinvertebrates during fixed flow rates (323 m³.s⁻¹ in the wet season and 111 m³.s⁻¹ in the dry season) and when peak flows fluctuated (378–481 m³.s⁻¹ in the wet season and 109–173 m³.s⁻¹ in the dry season) in 2010. Of the 31 924 organisms collected, 8872 individuals and 43 taxa were collected in the wet season and 23 052 and 32 taxa were collected during the dry season. Seasonality had a strong influence on invertebrate assemblage composition and structure in the drift. During fixed flow periods, drift densities were greatest in the dry season and drift taxonomic richness was greatest in the wet season. In the wet season, fluctuating flows increased nocturnal drift density and richness, but decreased diurnal richness; in the dry season, fluctuating flows decreased drift densities and diurnal richness. In conclusion, the daily and seasonal invertebrate drift patterns are influenced by dam operations that alter flows and this knowledge can be used to reduce the downstream effects of dams.