Following habitat restoration works undertaken on Newborough Warren National Nature Reserve in 2013 to create pioneer dune slacks and other early-successional habitats, surveys demonstrated rapid colonisation by a number of specialist invertebrates associated with these conditions. Additional excavations carried out in March 2015 provided an opportunity to investigate the speed and origin of this colonisation. Within two months, three pioneer dune slack beetles (Bembidion pallidipenne, Bledius subniger and Dyschirius politus) had colonised newly created habitat, despite previously being scarce on the dune system.

As it was suspected that colonising populations originated from estuarine habitats to the north and south of Newborough Warren, surveys were undertaken in the Cefni and Braint estuaries, together with the Afon Artro, Glaslyn and Dwyryd estuaries associated with Morfa Dyffryn and Morfa Harlech. Mapping of Bledius colonies indicated that these beetles were restricted to limited areas of recently deposited sand with low organic content, typically associated with estuarine and pioneer dune environments. Diatoms were found abundantly within the digestive tracts of Bledius beetles and appear to form an important food source.

Because pioneer dune slack habitat occurs only rarely on most Welsh dune systems, this study compared the invertebrate fauna of naturally occurring pioneer slacks at Morfa Dyffryn and Morfa Harlech with those of artificially created slacks on Newborough Warren. Surveys were undertaken at 20 sites using five pitfall traps per site and recorded 100,205 individual invertebrates representing 505 species. The principal taxa examined were beetles, spiders, harvestmen, millipedes, centipedes, woodlice and selected orthopteroid insects.

Analysis of vegetation and invertebrate data distinguished two habitat types at Morfa Dyffryn: true pioneer slack, characterised by damp, sparsely vegetated yellow sand, and post-pioneer slack, where increasing vegetation cover and biological soil crust development were evident. Principal Components Analysis demonstrated that the engineered slacks at Newborough Warren clustered closely with the natural pioneer slacks of Morfa Dyffryn, indicating that habitat restoration had successfully recreated conditions characteristic of naturally functioning dune systems.

Analysis of sixteen beetle species previously regarded by NRW as indicators of pioneer dune slack habitat suggests that several are more closely associated with post-pioneer slack conditions. The true pioneer dune slack beetle assemblage appears to be restricted to four species: Bembidion pallidipenne, Bledius fergussoni, Bledius subniger and Dyschirius politus, all of which also occur within estuarine habitats at the saltmarsh edge.

A supplementary survey of the tiger beetle Cicindela maritima found the species breeding successfully in damp pioneer slack habitat, further emphasising the conservation significance of these early-successional dune habitats and the importance of maintaining dynamic processes that create them.