Ecology of fishes of cave streams and other subterranean habitat

Abstract

Brazil is rich in caves, with more than 20,000 officially registered. In addition to the caves, which develop in different types of rock, there are other subterranean habitat (hypogean) with bodies of water in the form of drainages (level base streams), outcrops of the water table (saturated zone) in flooded caves or in the form of pools and lakes within caves, in addition to upper aquifers formed by infiltration of water in the rock. In some cases, groundwater does not emerge in caves, but in alluviums close to rivers, representing a hyporeic zone. The Brazilian subterranean ichthyofauna is composed of fish restricted to caves and other subterranean habitat (generally categorized as troglobites / stygobites) or species that have well-established populations in these habitat, but which also occur in streams and bodies of water on the surface (categorized as troglophilics). Currently, there are more than 80 species of fish with troglobitic and troglophilic populations in Brazil. Some population studies show estimates of varying population sizes and densities, generally characterized by small populations; a tendency towards a sedentary lifestyle; low condition factor values and life cycle strategies tending to K within the r-K continuum. These characteristics are related to the unique abiotic conditions of these habitat, such as low, infrequent and often unpredictable supply of nutrients, which can represent an accentuated filter. In relation to conservation, subterranean fish are threatened and most of the species formally described are included in lists of threatened fauna in Brazil. Only four species have been included and evaluated globally (Stygichthys typhlops, Pimelodella kronei, Phreatobius cisternarum and Phreatobius sanguijuela).