Common Standards Monitoring of Cave Invertebrate Assemblages

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The situation is somewhat better in Wales compared to other UK countries, where invertebrates in several cave systems within SSSIs are mentioned in citations. The most famous is the Ogof Ffynnon Ddu (OFD) National Nature Reserve, which is incorporated within the Ogof Ffynnon Ddu and Pant Mawr SSSIs in Powys. The geological and geomorphological interest of the OFD SSSI is centred on the cave and the fact that the undulating upland plateau above the system supports the finest limestone pavement in mid and southern Wales. The biological interest is due primarily to the list of scarce plant species on the plateau, but the citation also states: “the biological interest of the cave system itself has been extensively explored. A number of rare crustacean species restricted to subterranean habitats are of particular note. Part of the water catchment of the cave system is included in the SSSI in order to safeguard the invertebrate fauna and the active geomorphological processes requiring water”. However, the citation provides no further detail on the fauna of the cave system, which is especially of note for its diverse Collembola assemblage, nor the actual crustacean species, which include Niphargus fontanus Bate, 1859, Microniphargus leruthi Schellenberg, 1934, Proasellus cavaticus (Leydig, 1871), and Crangonyx subterraneus Bate, 1859, the latter known from just two other caves in Britain, both in the Cheddar Gorge of the Mendip Hills. 

The second longest cave system in Britain Ogof Draenen partially underlies the Gilwern Hill and Blorenge SSSIs near Abergavenny and although the cave Siambre Ddu, a large chamber directly above Draenen, to which it is connected via a fissure network too small for humans, but which allows the transit of bat species, is designated a SSSI on account of its importance as a roosting site for several bat species, Ogof Draenen itself has no formal conservation designation. There are numerous other designated sites across Wales that also include caves and mines within their boundaries. 

Although there are the few examples quoted above where mention is made of cave invertebrates, in most cases they have received little more than a footnote in the SSSI designations. Many surface SSSIs across Britain have been notified on the basis of their rare or unusual communities of invertebrates, either in combination with other features or as the sole designated feature. This state of affairs is undoubtedly due to a general lack of information and systematic recording of subterranean invertebrates, which is not surprising given their cryptic habitats and the extreme difficulties in being able to directly study such species in situ. 

Although there is a long history of biological recording in caves of the British Isles, systematic surveys of the invertebrate fauna of British caves are lacking, due to the general perceived scarcity of the fauna, resulting from localised extirpations during the repeated glacial cycles of the Pleistocene, and a lack of experienced cave biologists (biospeleologists). From 1938 to 1972 cavers, under the auspices of the Cave Research Group of Great Britain (CRG), collected specimens of invertebrates on an ad hoc basis which were then sent to various experts for determination. These paper records have recently been digitised by the biological recorder of the British Cave Research Association to form the Hazelton database, hosted on the BCRA website. This database forms a valuable set of historical information, but the records are now quite old and are almost entirely based on ad hoc collecting during caving trips. Some systematic surveys of British caves have been carried out but are either limited to just the aquatic fauna, or, with the exception of Pen Park Hole (Knight, 2014; 2017) require updating, such as the survey conducted in OFD in 1979. Some information can be gathered from analysis of the Hazelton data, but overall, the invertebrate assemblages of many British cave systems remain either unknown or poorly studied at best. This situation is not unique to Britain and was the theme of the 6thEurospeleo Protection Symposium held on the island of Vilm, Germany in October 2021, which aimed to assess current cave monitoring practices across Europe and provide recommendations for improvements in monitoring the EU habitat type (designated under the EU Habitats Directive) 8310 “Caves not open to the public”. 

To address this knowledge gap NRW have initiated a project to develop methods and undertake baseline surveys of cave invertebrate assemblages at two key sites, Ogof Ffynnon Ddu in the Swansea Valley and Ogof Draenen, near Abergavenny. This project will provide both baseline data for future condition monitoring of the two sites and an assessment of various sampling methods and their practicalities for assessing the invertebrate assemblages of other sites across the principality. This will be the first such initiative in the British Isles and could signal a new approach to the study of the subterranean biome within the UK. Surveys were initially carried out in both caves in May and June of 2023 with repeated sampling in winter (January & February 2024). The work was conducted by a small team led by Lee Knight, who carried out the surveys of aquatic habitats in both caves, whilst Julian Carter (National Museum Wales) and Andrew Lewington conducted surveys of the terrestrial element of the fauna.