Summary details for Centromerus semiater (L. Koch, 1879)

Distribution

This species has been recorded from only six sites in Britain: Wicken Fen in Cambridgeshire (1913), and in Norfolk, Woodbastwick Fen (1970), Wheatfen (1971), Catfield Fen in 1989 and again in 2006, and also from Reedham Marsh, Ludham and Common Fenn, Smallburgh in 2008 (Lott et al., 2010). The species has never been rediscovered at Wicken Fen, despite much recording. In Europe it has been recorded from Finland, Sweden, Russia, the Netherlands, Belgium, Germany, Poland, the former Czechoslovakia and Switzerland.

Habitat and ecology

In Britain the species has been found in litter and moss on the wet floor of sedge beds, in the litter layer of Calamagrostis canescens and Thelypteris palustris growing along the edge of fen waterways, in heaps of cut saw sedge Cladium mariscus and in open carr woodland and fen litter. In Europe it has been found in a much wider range of habitats including open pine and alder woodlands, willow scrub, Sphagnum bogs on heathland, reed-beds, various types of sedge vegetation and wet meadows. Clearly, this species is not confined either to basic or to acid vegetation types but occurs in a wide range of wet habitats. The only quantitative population data comes from Sweden where Almquist (1984) found it to be most abundant (1 individual m-2) in wet meadows with Molinia caerulea, Carex panicea and Filipendula vulgaris, followed by Cladium mariscus mire (0.6 individuals m-2) and lowest densities in Carex elata mire and a Sphagnum bog (0.3 individuals m-2).

Status

Restricted area of occupancy. Recorded from six hectads prior to 1992 but only known from three locations in two hectads after that date.

Threats

All known sites for this species lie within SSSIs. Woodbastwick Fen lies within the Bure Marshes NNR and Wicken Fen is a nature reserve owned by the National Trust. The principal threats in the Norfolk Broads are drainage of agricultural land and, in particular, abandoning of traditional management of sedge beds by summer mowing, leading to encroachment of scrub and carr woodland.

Management and conservation

Scrub invasion at Wicken Fen, a major problem in the recent past, is now being controlled by clearance of the scrub, annual mowing of the sedge beds, and grazing by Konik ponies and Highland cattle. At Woodbastwick Fen, sedge beds are mowed annually and Phragmites is cut which should help maintain suitable conditions for C. semiater. Heaps of sedge litter left in the fens are probably an additional benefit. Text based on Dawson, I.K., Harvey, P.R., Merrett, P. & Russell-Smith, A.R. (in prep.).