Benthic invertebrates of Rutland Water

The colonisation of Rutland Water by benthic invertebrates has been monitored from 1976 when the reservoir was first filled. A modified Ekman grab was used to sample populations quantitatively while false substrates and dredge samples were used to obtain supplementary data. Hand net and hand-sorting were used to study the littoral zone.The dominant taxa in the reservoir are Asellus aquaticus, A. meridianus, Gammarus pulex, Crangonyx pseudogracilis, Helobdella stagnalis, Erpobdella octoculata, Polycelis tenuis, larval Chironomidae and Oligochaeta. Other species which appeared abundantly, such as Limnaea pereger and Planorbis albus, have now disappeared and it is suggested that the generally low levels of gastropods might account for the poor performance of species such as Dugesia lugubris and Glossiphonia complanata.Other aspects of abundance are discussed, as are the effects of maturation of the system.