Aquatic invertebrates increase litter breakdown in Neotropical shallow semi-arid lakes

Abstract

The feeding behavior of shredders and scrapers (invertebrates) is important for litter processing in aquatic ecosystems. We assessed the importance of invertebrate activity for organic matter breakdown in shallow lakes (macrophyte covered or macrophyte free), testing whether the abundance of scrapers was greater than that of shredders, and if macrophytes increased scraper density and consequently, the rate of leaf litter breakdown. We used litter bags with senescent leaves to assess the density, richness and biomass of invertebrates and assessed the mass loss of litter after oven drying. The mean decomposition coefficient (k = -0.0037day−1) was lower than reported rates for other semi-arid lakes. We observed greater leaf breakdown in litter bags with coarse mesh, indicating the importance of scrapers, but potentially also microbes. However, leaf-associated invertebrates (averaged across both types of lakes) had low densities (4.7 ind.g−1), biomass (8.3 mg g−1) and richness (12 taxa), which may explain similar breakdown rates between lakes. Semi-aquatic Coleoptera and Mollusca were the most diverse taxa because they are capable of tolerating high hydrological stress associated with shallow lakes in semiarid areas. Planorbidae, which are intermediate hosts for the human parasitic trematode Schistosomamansoni, were almost absent in the macrophytic lake, suggesting that macrophytes may reduce the Planorbidae density and play an important role in human health.