Temporal variability of the macroinvertebrate community associated with Eichhornia azurea (Swarts) Kunth (Pontederiaceae) in a lake marginal to a tropical river

Abstract

Aquatic macroinvertebrates have a close relationship with associated floating macrophytes, especially with the roots. The plant root mass is an environment favorable to the development of the macroinvertebrate fauna, supplying both food resources and refuge against predators. The present study aimed to analyze the structure of the macroinvertebrate community associated with the roots of Eichhornia azurea (Sw.) Kunth (Pontederiaceae) in a lake marginal to a tropical river. Sampling was performed quarterly in three stands of E. azurea. One plant specimen was selected from each stand and five root mass samples were collected. The study was carried out in an extremely rainy year, with high rainfall in July, when the river level increased quickly, causing an extreme inundation and an increase in the root biomass of E. azurea. A higher abundance of macroinvertebrates was found in April, around four to five times the total density of the other periods. Taxa richness presented no significant temporal differences. Oligochaeta and Chironomidae were the predominant group of invertebrates in all periods. The extraordinary flood in June–July caused a modification in the macroinvertebrate fauna (an increase in the abundance and a reduction in the taxon richness), and was apparently a controlling factor for the community structure.