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Groundwater contains distinctive animals known as ‘stygobites’, which are adapted to live in the dark, have no pigment and no eyes, and are able to feel their way around.��They range in size from less than 1 mm to around 1 cm and occur in porous, fractured and karst aquifers. Stygobites can be found — and sampled — in caves, springs and boreholes.

���ճԹ� scientists have worked with a range of partners, including , the and the , to:

• investigate the occurrence and distributions of stygobite species in groundwater (Johns et al., 2015; Maurice et al., 2016; Weitowitz, 2017)
• assess their importance for UK biodiversity (McInerney et al., 2014)
• investigate their role in subsurface food webs (Weitowitz et al., 2019)

As some of the only truly endemic UK species, stygobites provide a unique and important contribution to UK biodiversity. Living in groundwater, sometimes far below the surface, they have survived millions of years of glaciations and climate change because groundwater is somewhat protected from the more extreme temperatures above ground (McInerney et al., 2014). Most UK fauna arrived at the end of the last ice age, when there was a land bridge to mainland Europe, but genetic studies have shown that some stygobite species are ancient endemics that have been here for millions of years (McInerney et al., 2014).

Hydrogeology and groundwater ecology

Groundwater ecology is often the domain of biologists and ecologists, but hydrogeological expertise can improve understanding of groundwater ecosystems (Maurice and Bloomfield, 2012). Working with UKCEH and using hydrogeological tools (for example, borehole packer testing and imaging), we developed new methods to investigate biological communities at different depths within the Chalk aquifer at a site in southern England (Sorensen et al., 2013). 

Work was also undertaken using geological and hydrogeological information to investigate habitat suitability for stygobite species and and identify potential geological barriers to dispersal, where low permability strata that form poor habitats are present (Johns et al., 2015; Weitowitz et al., 2017). 

Distribution and controls on stygobites in the UK

Between 2009 and 2017, ���ճԹ� and partners undertook surveys of stygobites in many different geological settings. The data from this work is available in the UK and discussed in Weitowitz (2017).

In a project led by Roehampton University, extensive sampling in south-west England revealed that stygobite species were signficantly less likely to be found in mudstone/siltstone or sandstone aquifers compared to carbonates and granites. In some areas, poor geological habitats appeared to create barriers that prevented species from colonising the adjacent, more suitable habitats (Johns et al., 2015).

The Chalk is a vital water resource in England and investigations of this aquifer, sampling 198 boreholes, revealed that it is also an important stygobite habitat (Maurice et al., 2016): 67 per cent of boreholes in the unconcealed Chalk contained stygobites. There was a clear north/south divide, which is thought to reflect effects of recent (Devensian) glaciation in northern England. Of the sampled Chalk boreholes in southern England, 77 per cent contained stygobites compared to 38 per cent in northern England. Only two stygobite species were found in northern England compared to six in southern England.

Surveying of 59 sites within the Ogof Draenen cave system near Abergavenny, south Wales, revealed high species diversity and abundance, suggesting that invertebrate communities in caves may have a role in biogeochemical cycles (Knight et al., 2018).

Further reading