Stygoregions--a promising approach to a bioregional classification of groundwater systems

Abstract

Linked to diverse biological processes, groundwater ecosystems deliver essential services to mankind, the most important of which is the provision of drinking water. In contrast to surface waters, ecological aspects of groundwater systems are ignored by the current European Union and national legislation. Groundwater management and protection measures refer exclusively to its good physicochemical and quantitative status. Current initiatives in developing ecologically sound integrative assessment schemes by taking groundwater fauna into account depend on the initial classification of subsurface bioregions. In a large scale survey, the regional and biogeographical distribution patterns of groundwater dwelling invertebrates were examined for many parts of Germany. Following an exploratory approach, our results underline that the distribution patterns of invertebrates in groundwater are not in accordance with any existing bioregional classification system established for surface habitats. In consequence, we propose to develope a new classification scheme for groundwater ecosystems based on stygoregions.

Figure 1. Stygobiontic invertebrates are perfectly adapted to groundwater habitats.

As a convergent evolutionary response to darkness, obligate groundwater animals are translucent, blind, exhibit enhanced tactile sense organs and lack circadian periodicity. Their bodies are elongated to vermiform facilitating locomotion in habitats with limited pore spaces. As an adaption to low and patchy food supply stygobites have slow metabolic rates, low reproduction rates and they exhibit longevity, compared to their surface water relatives. Shown are four frequently found representatives of the crustaceans; a) Niphargus laisi, Amphipoda; Schellenberg, 1936 b) Antrobathynella stammeri, Bathynellacea; Jakobi, 1954, c) Fabaeformiscandona spec., Ostracoda d) Proasellus slavus, Isopoda, Remy, 1948) (Pictures: K. Grabow).

Figure 2

a) European main ecoregions and b) a topographic map of Germany depicting the proposed stygoregions: Coloured areas show the major physiographic units (MPU), which were studied. The white areas compile MPU were no data was available. The colours refer to the individual stygoregions, which were delineated according to invertebrate distribution patterns found in groundwater. The affiliation of the Lower Rhine Valley is under debate, indicated by the blue-white hatching. Topographic map/GIS: http://www.eea.europa.eu/legal/copyright.

Figure 3. Non-metrical multi-dimensional-scaling plot (MDS) depicting biogeographical distribution patterns of groundwater dwelling invertebrates.

Symbols refer to a) freshwater surface systems according to the EU-WFD; b) stygoregions recommended for Central European groundwater systems. The labels of the symbols refer to the official German MPU (not listed in detail). Plotted are Bray-Curtis similarities of faunal means that were pooled for the major physiographic units of Germany.