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The South Wales Population
In May 2003 Dolomedes plantarius was discovered along a short section of the bank of the Tennant Canal where it forms the southern boundary of Pant-y-Sais National Nature Reserve (NNR), east of Swansea. In common with the English sites, this a lowland waterbody fed by neutral to alkaline, base-rich water. Open, stiff-leaved tussocks of tussock sedge (Carex paniculata) provide the main structure for nursery-web construction although webs are also found in the less robust reed sweet-grass (Glyceria maxima).
|Fig. 1 The Tennant Canal at Pant-y-Sais||Fig. 2 Pant-y-Sais National Nature Reserve||Fig. 3 One of the D. plantarius areas at Crymlyn Bog|
Surveys suggest that the spiders are much less abundant in what appears to be very suitable fen vegetation in the immediately adjacent Pant-y-Sais reserve. This is probably because, although they breed successfully there in some years, their population is limited by the small number of deep turf ponds that hold water throughout dry summers.
D. plantarius also occurs ca 2.5km further west along the course of the Tennant Canal, where it runs into Crymlyn Bog NNR. The full extent of the population at this site is not yet known because the depth of wet peat makes survey work both difficult and dangerous. Surveys commissioned by the Countryside Council for Wales (CCW) in 2003, 2004 and 2006Clark & Clark 2003, Clark 2004, Gallon 2007)show that D. plantarius has been present in at least four areas within Crymlyn Bog during this period. The bog is undergoing relatively rapid habitat change. Negative changes include the encroachment of scrub and reed (Phragmites australis) on formerly open areas of diverse fen vegetation. However, the introduction of pony grazing to counteract this is starting to reverse these trends, successfully opening-up some areas and restoring a richer and more structurally diverse fen flora.
A survey commissioned by CCW in 2001 looked unsuccessfully for evidence of D. plantarius in the extensive grazing marsh ditch systems of the Gwent Levels, further east on the coast of South Wales. A search of suitable habitat in Swansea Vale in 2003 was also unproductive (Gallon 2001).