Abstract
The karstic area of São Domingos, central Brazil, holds extensive drainage systems. In order to understand its biodiversity, various volumes of water were filtered with planktonic nets in stretches of subterranean and superficial rivers on five different occasions. We sampled four drips (152L), three calcite pools (368L), two subterranean rivers fed mainly by percolation water (6,395L), two subterranean rivers fed mainly by water coming from a sinkhole (4,175L) along different caves, one resurgence (158L), and four epigean rivers (101,690L). Physical and chemical variables were measured at some sites. Canonical Correlation Analysis was used to verify relationships between taxa and environment. The degree of similarity of the biota was assessed by cluster analysis (Sorensen, single linkage). There were records of exclusive taxa in epigean and subterranean samples, mainly in drips, which harbour the most unique fauna. The high richness of taxa presently recorded reveals the potential of the vadose zone biota in the tropical region, which was neglected in studies on Brazilian subterranean biodiversity. According to our results, the unsaturated zone tropical fauna may have different composition compared to that from temperate habitats. The studied communities were dominated by rotifers, while crustacean are predominant in the latter. The hypothesis can be clarified with the increase of long term studies and taxa identification at species level, besides the use of complementary sampling methods.
Highlights
Most of the subterranean habitats develop in karst systems, which are discontinuous geomorphic systems formed in soluble rocks and characterized by the presence of aquifers and conduits, with subterranean drainage (Dreybrodt 1988)
Thirty-six taxa were registered in all of the samples, belonging to different groups listed in decreasing order according to absolute/relative richness: Rotifera (23; 64%), Insect larvae (4; 11%), Copepoda-Cyclopoida, Calanoida and Harpacticoida (3; 8%), Cladocera (2; 5%), Dinoflagellata (1; 3%), Nematoda (1; 3%), Ostracoda (1; 3%) and Protozoa (1; 3%) (Table 2)
Some taxa were exclusive to one single sampling point: Anuraeopsis fissa and Euchlanis sp. (RTR); Bosmina sp. (PalmEp); Anuraeopsis sp. (AngEp); Brachionus sp. (SBerEk); Chaoboridae (AngEk); Simuliidae (BAraP), Arcella costata (AngD01), Brachionus falcatus, Conochilus sp., Filinia sp., Kellicotia bostoniensis and Keratella cochlearis tecta (AngD02)
Summary
Most of the subterranean habitats develop in karst systems, which are discontinuous geomorphic systems formed in soluble rocks and characterized by the presence of aquifers and conduits, with subterranean drainage (Dreybrodt 1988). These systems originate most caves that can reach hundreds of kilometres. In the upper section of the superficial layers of karstifiable rocks, a particular zone is formed - the epikarst (Mangin 1973) This consists of a heterogeneous system of openings in which surface water percolates through soil, retained for variable periods, potentially for years at a time (Jones et al 2004)
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