Associations of Aquatic Heteroptera at Woodwalton Fen, Huntingdonshire, and their Use in Characterizing Artificial Aquatic Biotopes

Abstract

Woodwalton Fen is an important National Nature Reserve, a short account of which was given by Duffey (1956). In order to maintain the wet conditions characteristic of fenland, water must be obtained from outside the reserve and distributed within it. The retention of floodwater, following overflowing of the drainage channels bordering the reserve, during subsequent dry periods is an important feature of management. Water may also enter the reserve from the drainage channels when they are full, but not overflowing, through a series of control points (Fig. 1). Such water is distributed by an internal system of connected dykes. There are about 11 miles (18 km) of dykes with a number of control points by which parts of the system can be isolated. Most of the dykes have a uniform width of 10 ft (3 m) at the top of the banks, decreasing to 8 ft (2.5 m) at the bottom of the dyke. The depth of water fluctuates considerably but 15 in. (40 cm) is about average. Before they were drained the East Anglian Fens must have supported an interesting and characteristic fauna and flora, including many aquatic species. Stephens (1829) mentions a number of aquatic Coleoptera recorded from Whittlesea Mere, which was drained in 1851. Despite drainage and intensive agriculture over most of the area, numbers of aquatic animals and plants have been recorded from the fragments of Fenland which remain. Although less thoroughly worked than Wicken Fen (Gardiner 1923-32), Woodwalton Fen is known to support many aquatic insects (Morton 1913; Balfour-Browne 1951; Gardner 1961; Buck 1962). These and other aquatic organisms have been maintained solely in the dykes and adjacent drainage channels, as there are no natural water bodies permanently in the reserve. The dyke system can therefore be regarded as fulfilling two functions: the distribution of water and the maintenance of aquatic animals and plants. More recently other bodies of water have been created in Woodwalton Fen. These include peat cuttings and ponds which resemble dykes but which are isolated from the system of distributing dykes. The diversification of habitats within a nature reserve is a normal object of management but is usually limited by available resources, by physical factors and by the fact that diversification not characteristic of the type of reserve under consideration is undesirable. Diversification of aquatic habitats may be achieved by manipulation of physical factors such as depth of water and speed of flow, and its degree of success can be assessed by reference to the whole or part of the fauna and flora inhabiting the different biotopes. In the study described here collections of aquatic Heteroptera (waterbugs) were made from chosen sites representative of the aquatic biotopes present on Woodwalton Fen. The ecology of these animals is relatively well known. In particular Macan (1954) and others have shown that definite associations of Corixidae occur in biotopes which can be