Distribution of a Population of Cognettia sphagnetorum (Enchytraeidae) in Relation to Microhabitats in a Blanket Bog

Abstract

Blanket bog covers most of the Moor House N.N.R. in Cumbria and the dominant faunal component of the peat is Enchytraeidae, in particular Cognettia sphagnetorum (Vedj.) (Peachey 1963; Springett 1963, 1967; Standen 1973). The enchytraeid population is aggregated to a variable extent throughout the year and Peachey (1963) and Springett (1967) suggested that aggregation of C. sphagnetorum results from animals moving towards areas of optimal environmental conditions. As part of the IBP studies at Moor House, C. sphagnetorum was extracted repeatedly from sites, to estimate annual net production (Standen 1973) and to provide animals for laboratory feeding studies (P. M. Latter & J. E. Howson, in preparation). The abundance of worms varied between samples of different vegetation types, and to investigate the causes of aggregation, further samples were taken during 1967-70 from three common vegetation types on a bog site at Moor House. Four series of samples were used in this study. (1) Samples (Standen 1973) taken at random, for the estimation of net production of C. sphagnetorum (production samples). (2) Seasonal samples taken from three microhabitats (microhabitat samples). (3) Samples taken on one date in relation to different surface litters and the depth of material in the upper layers of the bog profile (profile samples). The microbial content, moisture content and pH of these samples were examined as factors which might influence the distribution of the worms, and the gut contents of worms were also examined, to indicate variation in food intake in different microhabitats. (4) Seasonal samples taken at random, to assess seasonal variation in the food intake of the worms by the analysis of their gut contents (food samples). The results are discussed in relation to (a) the population distribution and (b) the factors affecting the distribution, using information from other IBP studies. These are referred to in the text as follows: production study (Standen 1973), field bait study (J. A. Springett & P. M. Latter, in preparation), feeding study (P. M. Latter & J. E. Howson, in preparation), all on Enchytraeidae, the litter decomposition study (Heal, Latter & Howson, in press) and the fauna decomposition study (V. Standen, in preparation).