Macroinvertebrate distributions and the conservation value of aquatic Coleoptera, Mollusca and Odonata in the ditches of traditionally managed and grazing fen at Wicken Fen, UK.
Water-filled ditches are an important ecological feature of lowland Britain. Originally dug to facilitate wetland drainage, ditches often provide refuges for aquatic flora and fauna of high conservation value. The ditches, ponds and major waterways of a traditionally managed undrained fen and the ditches of a previously drained cattle-grazed fen meadow were sampled at Wicken Fen National Nature Reserve for Coleoptera, Mollusca and Odonata, and for physical, chemical and biological variables. Multivariate analysis showed a clear division between ditches on the two fens, and between larger and smaller waterbodies. Individual ditches possessed distinctive faunas. Ditch age and bank profile were important factors influencing faunal species composition. Invertebrate distributions were shown to be significantly correlated with macrophyte distribution. Waterbodies were ranked in terms of their species quality, using a point-scoring system; there was no correlation between rankings for the three invertebrate groups; only ditch age and detritus levels were correlated with species quality score (for Coleoptera). Ditch management recommendations are discussed in the light of these results.