Global overview on groundwater fauna

Groundwater is an important global resource, providing water for irrigation, industry, geothermal uses and potable water. Moreover, groundwater contains the world's largest terrestrial freshwater biome with ecosystems, inhabited mainly by invertebrates (stygofauna) and microbes, undertaking important services including water purification, as well as nutrient and carbon cycling. Despite investigations on the spatial and temporal variations of groundwater fauna and the influence of environmental parameters on these organisms, in parts of the world, even the most basic knowledge of these ecosystems is still lacking. The aims of this study are to provide an overview on groundwater fauna (stygofauna) research, including the historical evolution of research topics and the development of sampling methods and secondly to identify the global distribution of groundwater fauna research and resulting data gaps. To achieve this, an extensive review of accessible groundwater fauna data was conducted by analysing 859 studies. It was evident that over time, there has been an exponential increase in the number of groundwater fauna studies together with changing paradigms in the research focus, particularly as sampling methods have developed from using simple nets, substrate samples and hand-pumps in the beginning to recent molecular analyses (e.g. ... mehreDNA). As application of molecular methods becomes more common, knowledge on groundwater diversity and functional ecology is expected to increase. Studies on groundwater fauna are spatially uneven and are dominated by research in Europe and Australia, with few studies in Africa, Asia and the Americas. This presently biased view on groundwater biota hinders the identification of biodiversity patterns and ecosystem functions on a wider geographic and climatic scale. In the future, a more evenly distributed stygofauna sampling effort in currently underrepresented areas of the globe is necessary to ensure a more comprehensive perspective on stygofauna biodiversity, roles and functional significances. This is increasingly important with the accumulating knowledge of the sensitivities of these ecosystems to anthropogenic activities, including climate change, and is fundamental to effective management of these ecosystems.