Assessment of abundance and community composition of benthic macroinvertebrates: recommendations for improved sampling, fixation and extraction of oligochaetes

For several decades, the abundance and community structure of benthic macroinvertebrates have been studied to assess the biological quality of aquatic ecosystems. Procedures aiming at studying the whole of macroinvertebrate communities were mainly designed for the evaluation of the diversity of insects at a site and are not adapted for assessing the effect of environmental factors on the community structure and abundance of specimen from other taxonomic groups, including oligochaetes. However, oligochaete abundance and community composition resulting from the implementation of such procedures have sometimes been used for establishing/complementing ecological diagnoses. Here, we propose a number of procedure adaptations, from the choice of the studied habitat, mesh sizes for the net and sieve, fixation of samples, to the sorting of specimens. Following these recommendations will allow to properly assess the effect of environmental factors on the abundance and community composition of oligochaetes at each of the sampled sites as well as make comparisons between sites possible. If procedures described herein are not adapted for the study of the whole macroinvertebrate fauna, oligochaetes and the other macroinvertebrates should be analyzed separately.