Patterns of macroinvertebrate production and energy flow in headwater streams of the Brazilian Savanna

Secondary production estimates are an important element of ecosystem ecology because they facilitate quantification of the roles of consumers in material and energy cycling. We estimated production and resource consumption of stream macroinvertebrates, along with stream metabolism and organic matter storage in 3 relatively undisturbed Savanna headwater streams in southeastern Brazil. We measured production of benthic macroinvertebrates and reach-scale metabolism from October 2015 to September 2016. Mean annual values of gross primary production and ecosystem respiration varied from 0.06 to 0.22 and 3.96 to 23.76 g O₂ m²² d²¹, respectively, reflecting net heterotrophic conditions. Total secondary production ranged from 11.0 to 13.5 g ash-free dry mass m²² y²¹. Gatherers, shredders, and predators were the most important contributors to production, ranging from 11 to 30%, 21 to 39%, and 20 to 49% of total production, respectively, and detrital pathways accounted for most energy flow. Shredders only ingested 3.4 to 8.1% of total available food resources, suggesting that food resource availability does not limit production in these streams. To our knowledge, this study provides the first quantification of energy flow patterns in Brazilian Savanna streams using secondary production estimates and is one of the few measuring growth rates and secondary production of macroinvertebrates with short generation times under field conditions in tropical streams. Furthermore, this study is one of the few to link stream metabolism and organic matter storage to secondary production. Our results will help to understand reference conditions in the poorly studied streams of a region particularly threatened by human activities and potentially elsewhere in tropical systems.