Chapman, L.: The Respiratory Ecology of Benthic Macroinvertebrates in a Swamp-River System in East Africa

Hypoxia (oxygen scarcity) is widespread in tropical freshwater systems, particularly in dense swamps, and may be an important factor structuring benthic macro-invertebrate communities. Benthic macro-invertebrates show a broad diversity of respiratory modes ranging from atmospheric breathers to tracheal gills. These adaptations have associated costs and benefits that vary with ecological backgrounds and affect the ability of aquatic invertebrates to use hypoxic water. The objectives of this study were to (a) describe the benthic macro-invertebrate community from nine sites in Kibale National Park, Uganda and (b) determine the degree to which dissolved oxygen can explain variation in respiratory guilds. There were distinct differences among sites in the occurrence of respiratory guilds and in their relative abundance. Across all sites, the percent relative abundance of atmospheric breathers was negatively correlated with concentration of dissolved oxygen, while the relative abundance of tracheal gill breathers was positively correlated with dissolved oxygen. Invertebrates with permanent or temporary air storage (transportable stores) were only found in high abundance in well-oxygenated flowing water. Seasonal differences in the relative abundance of respiratory guilds were most pronounced in the papyrus swamp site where dry season conditions produce extremely hypoxic waters (<1.0 mg/L). In the dry season the swamp was characterized by fewer respiratory guilds and a higher abundance of atmospheric breathers than during the wet season. Although other environmental characters may influence the composition of benthic macro-invertebrates communities, dissolved oxygen concentration seems to be a good predictor of respiratory guild abundance and a key factor in maintaining invertebrate faunal structure and diversity.