Changes in the structure and composition of freshwater oligochaete fauna in response to different types of tropical springs, Brazil

The aquatic oligochaete fauna from 71 tropical springs was studied to investigate the role of spring typology and environmental variables in the structuring and composition of assemblages. Multivariate analyses showed that, in general, limnocrene and rheocrene springs ordered themselves closer to each other than to helocrene springs, suggesting higher environmental and faunistic similarities between them. Helocrene springs were shallower, rich in total phosphorus and nitrogen, with a predominance of finer fractions of substrate, and occurred in lower altitude areas. We have found differences in abundance, richness, and composition of oligochaetes in springs of the helocrene type, but not between the other crenal types. Changes in the structure and composition of assemblages may be related to the changes in substrate composition (granulometry and nutrients). The most abundant family was Enchytraeidae, and the Naididae family was the most diverse. We concluded that the abiotic conditions of different types of springs influence the way oligochaete assemblages are structured. This study is the first in Brazilian springs and our results contribute to the understanding of the relationship between the oligofauna and the environmental variables in tropical spring habitats. In addition, it provides information on the neotropical biodiversity of oligochaetes.