Habitats and Diversity of Subterranean Macroscopic Freshwater Invertebrates: Main Gaps and Future Trends

Abstract

Caves are the best studied aquatic subterranean habitat, but there is a wide variety of these habitats, ranging in depth below the surface and size of the spaces (pore or habitat size). Both factors are important in setting limits to species composition and richness. In addition to caves, among the most important shallow aquatic subterranean habitats are the hyporheal (underflow of rivers and streams), the hypotelminorheal (very superficial drainages with water exiting in seeps), epikarst, and calcrete aquifers. Although it is little studied, both body size and species composition in the different habitats is different. Because of high levels of endemism and difficulty in access, no subterranean habitats are well sampled, even caves. However, there are enough data for robust generalizations about some geographic patterns. Individual hotspot caves are concentrated in the Dinaric region of southern Europe, and overall, tropical regions have fewer obligate aquatic cave dwellers (stygobionts). In all subterranean aquatic habitats, regional diversity is much higher than local diversity, but local diversity (especially single cave diversity) may be a useful predictor of regional species richness. In Europe there is a ridge of high aquatic subterranean species richness basically extending east from the French–Spanish border. Its cause may be either high productivity or that long-term temperature oscillations are at a minimum. With increased collecting and analysis, global and continental trends should become clearer.

Invertebrate traits, diversity and the vulnerability of groundwater ecosystems

“…However, not all stygobitic invertebrates are capable of burrowing, with many utilising existing voids in the matrix. For these non‐burrowing taxa, there is frequently a relationship between the body size and habitat pore size (Dumnicka et al, 2020; Korbel et al, 2019). The minute voids present in unconsolidated sediments of alluvial aquifers are a spatial constraint for even small stygobitic cyclopoids and harpacticoids, which often have reduced body size, shortening of the swimming legs and a reduction in setation of the cephalic appendages relative to surface water species (Bruno et al, 2009; Galassi, 2001).…”

“…Given their low energy, groundwater environments typically support low biomass and diversity of taxa. However, isolation and fragmentation have given rise to a high degree of short-range endemism (Harvey et al, 2002), with typically few species in any one location, but many species across locations (Dumnicka et al, 2020). The pressures of the groundwater environment have led to a range of convergent and divergent evolutionary processes within and among groundwater invertebrate species.…”

Subterranean Waters of Yucatán Peninsula, Mexico Reveal Epigean Species Dominance and Intraspecific Variability in Freshwater Ostracodes (Crustacea: Ostracoda)

“…Global patterns of biodiversity and endemicity in subterranean waters are largely varied among regions and are influenced by factors such as subterranean water availability, the geological and climatic history of the region and the capacity of the organisms to succeed in these environments [2,[13][14][15]. In tropical regions for example, the biodiversity of obligate aquatic cave dwellers is overall lower than that in temperate regions [16,17], but large tropical regions remain unexplored.…”