Tanja Pipan

Temperature variation and the presence of troglobionts in terrestrial shallow subterranean habitats

Within the soil matrix and underlying rock, cracks and fissures and other air-filled spaces between rocks, sometimes called the milieu souterrain superficiel (MSS), are present in a variety of geological contexts. We examined year-long hourly temperature profiles at sites in lava in the Canary Islands and limestone in Slovenia. All sites had species that show morphological adaptations usually associated with cave-dwelling organisms, including elongated appendages and reduced eyes and pigment. MSS sites were studied at depths between 10 and 70 cm and showed strong seasonality, and most had a discernible diurnal cycle as well. The most striking difference from surface habitats was that the temperature extremes were much less pronounced in MSS sites. Temperature variability was not correlated with troglobiotic species richness. The presence of species with similar morphologies to those found in caves indicates that selective pressures are similar in cave and shallow subterranean habitats.

Morphological Differences Among Eyeless Amphipods in the Genus Stygobromus Dwelling in Different Subterranean Habitats

Abstract The amphipod genus Stygobromus occurs in a variety of subterranean habitats in North America, including caves, phreatic (groundwater) lakes, and superficial subterranean habitats (seeps and epikarst). The habitats share the absence of light but differ in other features, such as pore size of the habitat, available food, and degree of seasonality. Measurements of body size, antennal size, and antennal segment number of type specimens were compared for 56 species occurring in the eastern United States. Except for differences in body size, differences among species in the four different habitats were not significant. Body size was related to relative pore size of the habitat, e.g., epikarst, with the smallest spaces, had the smallest species. However, in all habitats, there was one very large species (> 15mm); these enigmatic species apparently occupy a distinct ecological niche, perhaps being more predatory. Differences in relative antennal size showed no significant differences among habitats, and differences in number of antennal segments were marginally significant (P  =  0.06) among habitat types and not in the predicted pattern. Differences among habitats in seasonality and available food seemed to be a minor part of the selective environment; absence of light seemed to be a major part of the selective environment.

Dynamics of Epikarst Communities: Microgeographic Pattern and Environmental Determinants of Epikarst Copepods in Organ Cave, West Virginia

Abstract The copepod community occurring in the uppermost part of karst was investigated by collecting animals from 13 ceiling drips in Organ Cave, West Virginia, over a 30 d period. A total of 444 copepods belonging to six genera and ten species were found. There was considerable heterogeneity, both spatially and temporally. Among physical parameters (oxygen, drip rate, conductivity, temperature, pH, ceiling thickness and redox), overall abundance was strongly influenced by drip rate. Community composition, analyzed by Canonical Correspondence Analysis, was correlated with drip rate, oxygen and ceiling thickness. Community similarity, as measured by Jaccard index, declined with geographic distance, but after a distance of several hundred meters, the average similarity and range of values increased, as “new” communities appeared. The overall pattern appears to be a relatively fine-scale patchwork of communities at a scale of hundred or so meters. The hotbed of copepod diversity in caves is the epikarst, not the streams.

Spatial and temporal patterns in abundance and character of dissolved organic matter in two karst aquifers

The spatial and temporal patterns in concentration and character of dissolved organic matter (DOM) in karst basins in Slovenia and the United States were characterized. DOM in the shallow aquifer, or epikarst, waters was characterized by low, stable concentration and compounds of low aromaticity and humification. There was strong temporal coherence in DOM character, but not concentration, across locations within the epikarst. DOM in sinking streams, cave streams, and resurgence springs typically had higher DOM concentration and aromaticity. Fluorescence and parallel factor analysis of DOM revealed that humic or fulvic-like substances in soils, surface and cave streams, and springs were the dominant fluorophores. However, DOM extracted from soils was chemically different from that present in the stream and spring waters. Epikarst water contained humic-like and protein-like DOM, and had fluorescence characteristics indicative of microbial uptake and release of DOM in the epikarst. These data show that there are substantial basin-scale patterns in DOM concentration and character and that aquifer structure influences the spatial patterns of DOM in karst groundwater.

Forty Years of Epikarst: What Biology Have We Learned?

Epikarst is not only an important component of the hydrogeology of karst and an active site of speleogenesis, it is habitat for a number of species adapted to subterranean life. Water in epikarst, with a residence time of days to months, is a highly heterogeneous habitat, and the animals are primarily sampled from continuously sampling dripping water or collecting from residual drip pools. While the subterranean fauna of cracks and crevices has been known for over 100 years, it is only in the past several decades that epikarst has been recognized as a distinct habitat, with reproducing populations of stygobionts. Dissolved organic carbon in epikarst drip water is a primary and sometimes the only source of organic matter for underlying caves, especially if there are not sinking streams that enter the cave. Typical concentrations of organic carbon are 1 mg L -1 . The fauna of epikarst is dominated by copepods, but other groups, including some terrestrial taxa, are important in some areas. Most of the diversity is β-diversity (between drips and between caves). In Slovenia, an average of nearly 9 stygobiotic copepod species were found per cave. In studies in Romania and Slovenia, a number of factors have been found to be important in determining species distribution, including ceiling thickness, habitat connectivity and habitat size. In addition to eye and pigment loss, epikarst copepod species may show a number of specialization for life in epikarst, including adaptations to avoid displacement by water flow. Several geoscientists and biologists have challenged the uniqueness and importance of epikarst, but on balance the concept is valid and useful. Fruitful future research directions include development of better sampling techniques, studies to explain differences among nearby epikarst communities, phylogeographic studies, and assessing the possible role of copepods as tracers of vadose water. adaptation; cave ecology; Copepoda; stygobionts; subterranean biodiversity

Shallow Subterranean Habitats

Shallow subterranean habitats (SSHs) are aphotic subterranean habitats relatively close to the surface ( milieu souterrain superficiel (MSS), and consist of the spaces between rocks, rock cracks, and the like. All of these habitats are more variable than caves, typically with a pronounced annual temperature cycle. Available organic matter is also higher in SSHs than in caves. The importance of SSHs as gateways to the subterranean realm is not known, but it is clear that they contain species both modified for subterranean life, and unique to these habitats.

The blurred line between photic and aphotic environments: a large Mexican cave with almost no dark zone

*dculver@american.edu Citation:

The unity and diversity of the subterranean realm with respect to invertebrate body size

A variety of subterranean habitats share an absence of light and a dependence on allochthonous productivity, but they differ in many features, including habitat volume. We examined the hypothesis that habitat volume is an important factor in community organization, especially with reference to body size, for a variety of communities for which data were available. We analyzed the results of ten studies that compared body sizes of obligate subterranean dwelling species with respect to habitat. All of the studies confirmed the hypothesis that habitat size was an important determinant of body size. However, surprisingly little information is available on the relationship between body size and habitat size, and only two of the studies reported directly on the size of habitat spaces. Habitat size appears to be an important determinant of body size in subterranean species, but more detailed studies, especially of habitat (pore) size are needed.

Analyzing climate change and surface-subsurface interactions using the Postojna Planina Cave System (Slovenia) as a model system

Worldwide, there are at least 12 ILTER sites with an emphasis on karst, landforms arising from the combination of high rock solubility and well-developed solutional channel porosity underground, but the study of cave ecosystems has been largely neglected. Only two ILTER sites, both in Slovenia, are primarily caves. Caves are under-represented for several reasons, but especially because of the overall difficulty of access and the lack of a clear research agenda for cave ecosystem studies. We review several aspects of long-term studies in Postojna Planina Cave System (PPCS), proposing our approach as a model for ILTER research in caves. In PPCS, analysis of short-term temperature data shows a muted daily cycle and seasonality, and analysis of long-term temperature data shows an increase, largely the result of climate change. Changes in drip rate of epikarst aquifers above the cave are correlated with rainfall but with lags and complications resulting from differences in longer term rainfall patterns. Analysis of discharge rates indicates a rapid response to precipitation not only in the Pivka River at its sinking, but also at Unica Spring, where discharge is augmented from other parts of the aquifer, including epikarst. Quantitative analysis of the obligate epikarst-dwelling copepod community shows that, unlike most cave communities, complete sampling of the fauna is possible. Finally, organic carbon levels in PPCS indicate likely carbon limitation in the system. These five factors (temperature, drip rate, river discharge, epikarst copepod fauna, and organic carbon) are the appropriate variables for capturing the essential long-term trends in cave ecosystems and their causes.

Partitioning diversity in subterranean invertebrates: The epikarst fauna of Slovenia

The decomposition of diversity into within site (α) and between site (β) components is especially interesting in subterranean communities because of their isolated nature and limited dispersal potential The aquatic epikarst fauna, sampled from water drips in caves affords a unique opportunity to provide comparable, quantitative samples of a portion of the obligate subterranean dwelling fauna in multiple hierarchical levels. We focused on three interrelated questions—(1) what is the spatial pattern of epikarst species diversity; (2) how does species diversity partition between local, and regional components (nested and replacement); and (3) whether epikarst hotspots are subterranean hotspots in general. We analyzed the geographic pattern of species richness of 30 species of obligate subterranean copepods found in 81 drips in Slovenian caves in three karst regions—Alpine, Dinaric, and Isolated. Comparison of Chao1 and observed (Mao-tau) estimates of species richness indicated sampling in most drips was complete, but species accumulation curves indicated roughly half of the sites in the Dinaric karst had not reached an asymptote. Overall, within drip diversity accounted for three species, different drips in a cave another three, different caves in a region six species, and different regions accounted for the remaining 18 species. Sites in the Dinaric karst had much higher species richness than the other sites, which is in agreement with studies of other components of the subterranean fauna. The fauna associated with drips in Županova jama (jama = cave), in the east-central Dinaric karst was the richest found. While turnover explained the majority of β-diversity, nestedness in the form of hotspot drips was important as well. A consequence is that a small number of drips largely determine cave and regional species diversity.