Response of benthic cave invertebrates to organic pollution events

1. Even though the fragility and vulnerability of subterranean ecosystems (caves, groundwater and hyporheic habitats) is widely acknowledged, the impacts of anthropogenic disturbances have been poorly quantified when compared to surface waters. In particular, limited data exist regarding the impact of organic pollution upon aquatic cave invertebrate communities. 2. The Peak-Speedwell Cavern system (Derbyshire, UK) was affected by two organic pollution events, during a 7–year study (1997-2003), originating from the same source in the surface catchment but resulting in markedly different ecological responses. The first event led to the elimination of most taxa from affected sites while the second resulted in an increase in abundance of organisms within the cave associated with the increased availability of trophic resources. The second event also coincided with the invasion of the stygophilic amphipod, Gammarus pulex, at a site where it had not previously been recorded. 3. Recovery of the invertebrate community following both organic pollution events occurred within 12-months. Recolonisation of the affected sites was facilitated by annual flooding of the cave and by the presence of refugia on unaffected subterranean tributaries. 4. The data highlight the problems associated with the conservation and management of subterranean ecosystems where impacts in distant surface catchments may have unseen repercussions for the subterranean environment. Aquatic subterranean habitats are not widely monitored and the impacts of pollution/disturbance may not be detected in surface waters for some time, if at all, due to dilution effects. Caves supporting obligate subterreanean organisms (stygobites) are particularly vulnerable to these pressures and require clear management strategies to protect both the subterranean and surface catchments which support them.