The ecology of Riparian Carabidae (Coleoptera) in a regulated river system

Rivers and riparian zones are among the most threatened ecosystems globally, with modification of their natural flow regime a major source of change. Exposed riverine sediments (ERS) are characteristic of unregulated rivers in their upper and middle reaches and among the few remaining natural riparian habitats. However, they are in decline across the UK and Europe as a result of widespread modifications to channel structure and flow regimes. Studies of ERS and their dependent carabid beetles can help to understand how environmental change is affecting river ecosystems more generally, but prolonged research is scarce. This thesis reports on a three year study of carabid beetles at multiple sites in the Usk river system, Wales, during an extended period of low river discharge. Plot-scale experimentation and reach-scale surveys showed consistently that carabid assemblage structure and distribution varied more strongly in response to time and across the reach than to within-patch habitat character. There was no evidence of carabid assemblage succession, though generalist species richness appeared to increase through the study as specialist species richness declined, and general conditions for specialist species may have declined. It is suggested that specialist carabids of high conservation importance could be squeezed as land use encroachment and river regulation causes a decline in the ERS resource. Management interventions at the reach- or catchment scale are advocated to maintain and restore the ephemerality of ERS. Being responsive to reach- and catchment scale events, exposed riverine sediments and their dependent fauna should be the focus of long term study to appraise rates of environmental change or resilience to anthropogenic stressors. In particular, long term studies may not only reveal trends on ERS towards homogenisation, indicative of environmental decline within the wider river system, but might also help to detect the effectiveness of river restoration

Squeezed out: the consequences of riparian zone modification for specialist invertebrates

While anthropogenic biodiversity loss in fresh waters is among the most rapid of all ecosystems, impacts on the conservation of associated riparian zones are less well documented. Riverine ecotones are particularly vulnerable to the combined ‘squeeze’ between land-use encroachment, discharge regulation and climate change. Over a 3-year period of persistent low discharge in a regulated, temperate river system (River Usk, Wales, UK; 2009–2011), specialist carabid beetles on exposed riverine sediments (ERS) were used as model organisms to test the hypotheses that catchment-scale flow modification affects riparian zone invertebrates more than local habitat character, and that this modification is accompanied by associated succession among the Carabidae. Annual summer discharge during the study period was among the lowest of the preceding 12 years, affecting carabid assemblages. The richness of specialist ERS carabids declined, while generalist carabid species’ populations either increased in abundance or remained stable. Community composition also changed, as three (Bembidion prasinum, B. decorum and B. punctulatum) of the four dominant carabids typical of ERS increased in abundance while B. atrocaeruleum decreased. Despite significant inter-annual variation in habitat quality and the encroachment of ground vegetation, beetle assemblages more closely tracked reach-scale variations between sites or catchment-scale variations through time. These data from multiple sites and years illustrate how ERS Carabidae respond to broad-scale discharge variations more than local habitat character. This implies that the maintenance of naturally variable flow regimes is at least as important to the conservation of ERS and their dependent assemblages as are site-scale measures

Protected Areas and Nature Recovery: Achieving the goal to protect 30% of UK land and seas for nature by 2030

This report from the British Ecological Society (published 22 April 2022) examines the Prime Minister’s pledge to protect 30% of UK land and seas by 2030 to support nature recovery