Observations on the Planktonic and Profundal Crustacea of the Lakes of the English Lake District

Previous work on the planktonic Crustacea of this district has been limited in scope. The records of Norman & Brady (1867), Brady (1868), Beck (1883) and Pratt (1898) were brought together by Scourfield (1903) in his Synopsis of British Entomostraca. The first attempt to investigate the planktonic Crustacea of all the lakes in the district was that of Gurney (1923) but valuable though this work was in providing an account of the species composition of the lakes, it yielded. no seasonal or quantitative data since most of his material had been collected near the surface with a phytoplankton net at only one season. Filteau (1958, 1959) compared life-cycles and seasonal changes in number of planktonic Crustacea in Windermere, Esthwaite Water, Bassenthwaite Lake and Ennerdale Water from January to December 1956, but only summaries of this work have been published. Studies on vertical distribution (Cushing 1955; Ullyott 1939) and on horizontal distribution (Colebrook 1960) have been made in Windermere. Wailes (1939) gives a species list of Cladocera and Rotifera for the two basins of Windermere. A study of the copepod Cyclops leuckarti,* in Esthwaite Water, over 3 years, was made by Smyly (1961). For comparison with the results of Gurney (1923) the lakes have been arranged (Table 1) according to their phytoplankton in the groups to which Pearsall (1921, p. 275) assigned them. Pearsall divided the lakes into four groups, which he named primitive, intermediate, evolved and most evolved, according to the amount of silting of their beds. The distribution of the phytoplankton corresponds fairly well with these groups, especially at the ends of the series. For example, the unproductive lakes, such as Wastwater and Ennerdale are low in nutrients, have few diatoms and no typical planktonic blue-green algae: the productive lakes, such as Esthwaite Water, are high in nutrients, and have diatoms and some blue-green algae. To compare the zooplankton with the phytoplankton, Gurney (1923) used the same groups as Pearsall. I have used here essentially the same basis for comparison but in the light of the results of recent research have made a few additions and alterations. Thirlmere has been added to group I. A new group, III a, is introduced to bring in Brothers Water, Elterwater and Rydal Water and to this new group Grasmere is transferred from group IV. Loweswater and Blelham Tarn have been added to group IV. Windermere was not sampled in this survey but for the sake of completeness is included in Table 1: the species list shown for this lake is taken from Gurney (1923) and Wailes (1939). The species list (Table 1) is essentially the same as that of Gurney (1923), except that the two mainly littoral species, Polyphemus pediculus and Sida crystallina are omitted, the different species of Daphnia are considered to be varieties of D. hyalina, Cyclops abyssorum Sars is assigned to C. strenuus abyssorum Fischer and the rotifer, Asplanchna priodonta has been added.