High water flow velocity reduces beta diversity and leads to a distinct composition of Oligochaeta in Neotropical lotic ecosystems

Abstract

Water flow velocity is a strong environmental filter structuring benthic communities in lotic ecosystems. While many studies have determined its effect on the distribution and diversity patterns of insects, the role of water flow velocity on other groups of aquatic invertebrates (i.e., Oligochaeta) has remained unexplored. We sampled five lotic ecosystems to investigate the influence of water flow velocity on the species composition of Oligochaeta assemblages in a Neotropical floodplain. Our first hypothesis was that higher water flow velocity decreases Oligochaeta assemblages variability. Consequently, we expected a lower beta diversity among the mid-channels of the ecosystems (i.e., sites with higher water velocity) relative to channel margins (i.e., sites with lower water velocity). Our second hypothesis was that water flow velocity determines species composition of Oligochaeta. Consequently, we expected a different species composition between the mid-channel and the channel margins of lotic ecosystems. We found 19 Oligochaeta species across the five lotic ecosystems. We corroborated both hypotheses because we found lower Oligochaeta beta diversity among the mid-channels of the lotic ecosystems as well as a different species composition. Haplotaxis aedeochaeta and Narapa bonettoi were the taxa strongly associated with the mid-channel, because they are adapted to live among the sand grains in the bottom of the rivers with high depth and water velocity. Overall, water flow velocity should be considered as a strong driver of Oligochaeta species composition.