Current status
The fen raft spider is a wetland spider dependent on permanent, standing or slow moving water. It is associated with nutrient-poor water of near neutral or alkaline pH. It lives on the surface of pools and ditches, and amongst emergent vegetation; typically it hunts from `perches` on stems emerging from the water, taking a wide range of invertebrate prey on or below the surface. Emergent, stiff-leaved vegetation in open, sunny conditions is also required for the construction of nursery webs in which the young are reared.
There are no reliable records of this species in the UK before its discovery in 1956, at Redgrave and Lopham Fen, on the Norfolk/Suffolk border. In 1988 it was discovered at a second site, the Pevensey Levels, Sussex, c160 km away. The Redgrave and Lopham Fen population has contracted progressively in range over the last 30 years and is now restricted to two, small, isolated centres. Since systematic monitoring began in 1991, numbers in these areas have fluctuated around very low levels, with no detectable temporal trends. The total population, probably of little over 100 adult females in most years, is highly vulnerable to stochastic extinction. The only survey of the Pevensey population in 1992 estimated that there were over 3000 adult females. The fen raft spider has been recorded throughout the Palaearctic. Under recording and confusion over identification make assessment of status difficult, but it appears to be declining and often under threat of extinction in western and central-southern Europe whilst remaining well established in Scandinavia and the Baltic States.
In Great Britain this species is classified as Endangered. It is given full protection under Schedule 5 of the Wildlife and Countryside Act 1981.
Current factors causing loss or decline
Water abstraction.
Inappropriate ditch management.
Deterioration in water quality.
Loss of suitable wetland habitat.
Current action
Most of the Pevensey population occurs within the Pevensey Levels NNR/SSSI complex. The population at Redgrave and Lopham Fen occurs within an NNR, which is included within the Waveney and Little Ouse Valley Fens candidate SAC.
The fen raft spider has been the subject of an NE Species Recovery Programme since 1991.
Habitat restoration, initiated in 1993 at Redgrave and Lopham Fen by the Suffolk Wildlife Trust, with grant-aid from the EU Life Fund, has involved restoration of the fen`s natural hydrology, extensive peat-stripping, scrub clearance and grazing.
Action plan objectives and targets
Achieve a ten-fold increase in the range of the population at Redgrave and Lopham Fen.
Increase the population density throughout much of the range of Redgrave and Lopham Fen to a mean maximum of c15 individuals per pool (the maximum level supported since monitoring began in 1991).
Maintain the density of the fen raft spider on the Pevensey Levels.
Maintain the range of the fen raft spider on the Pevensey Levels.
Introduce populations to two suitable new sites by 2010.
Proposed actions with lead agencies
Policy and legislation
Where appropriate, include the requirements of the species when revising prescriptions for relevant agri-environment schemes. (ACTION: NE, MAFF)
Address the requirements of this species in the LEAP process and in relevant WLMPs. (ACTION: EA, IDBs, LAs, MAFF)
Take account of the requirements of the species in response to applications for water abstraction licences. (ACTION: EA)
Site safeguard and management
Where possible, ensure that occupied and potential habitat is appropriately managed, including the maintenance of water quality and water levels, by 2005. (ACTION: EA, NE)
Ensure that the species is included in site management documents for all relevant SSSIs. (ACTION: NE)
Species management and protection
Translocate spiders within existing sites where physical isolation prevents recolonisation of suitable habitat. (ACTION: NE)
Introduce to a series of new sites in East Anglian and southern England to establish a new viable population in each region. (ACTION: NE)
Advisory
Advise landowners and managers of the presence of the fen raft spider and the importance of beneficial management for its conservation. (ACTION: NE).
Future Research and Monitoring
Continue regular monitoring at Redgrave and Lopham Fen, and establish a regular monitoring programme for the species at Pevensey Levels and for newly established populations. (ACTION: NE)
Conduct targeted autecological research to inform habitat management. (ACTION: NE)
Encourage research on the ecology and conservation of this species on an international level, and use the experience gained towards its conservation. (ACTION: NE, JNCC)
Communications and Publicity
Promote opportunities for the appreciation of this species and the conservation issues associated with its habitat. This should be achieved through articles within appropriate journals, and by a publicity leaflet, as well as by increasing opportunities for public viewing. (ACTION: NE)
Links with other action plans
None given.
Local implementation
The following LBAPs are working on Dolomedes plantarius:
Publication details
Originally published in: UK Biodiversity Group Tranche 2 Action Plans - Volume IV: Invertebrates (March 1999, Tranche 2, Vol IV, p429)
Related links
ARKive Visit the ARKive website to view images and further information relating to this species