Transitory aquatic taxocenosis in two neotropical limestone caves

Abstract

In karstic environments, water recharge areas are characterized by external features that capture and convey the surface water to subterranean compartments. The objective of the present study was to evaluate the effects of the short term natural water level fluctuations on the composition and abundance of the zooplankton and ichthyofauna inside two limestone caves. Zooplankton was sampled with filterings nets (120µm) and fish, with trawl nets, gillnets, wicker trap and hand nets. In both caves the rainwater is filtered through the exokarst directly above the caves and drips from speleothems. It can also come in flash floods, be filtered by the soil, or come through dolines, partially flooding the floors of the caves on its way to supply the water table. Through flooding clay, trunks, leaves and bovine feces are transported that accumulate on the floor of the caves. Three groups of invertebrate zooplankton were found in the two caves (Copepoda, Protozoa and Rotifera) and 3 benthic/nektonic taxa (Annelida, Culicidae and Hyalella sp.). Eleven species of fish were captured in Characiforms (Astyanax sp, Astyanax bimaculatus, Astyanax fasciatus, Serrapinus heterodon, Cheirodon piaba, Cyphocharax gilberi, Hyphessobrycon santae, Characidium lagosantense, Hoplias malabaricus) and Siluriforms (Rhandia quelen and Hoplosternum littorale). The flood events in the two caves, caused by the water table level increase and flash floods during the rainy period allow fish and zooplankton species, originating from the epigean environment, to have access and explore areas in the cave that are inaccessible during the dry season. At the end of the rainy season those organisms trapped in temporary bodies of water die and can serve as a food resource for other terrestrial species.