The Água Clara Cave System in Northeastern Brazil: The Richest Hotspot of Subterranean Biodiversity in South America

Abstract

The Água Clara Cave System (ACCS) in Brazil is the richest hotspot of subterranean biodiversity in South America. In this study, we present an updated list of cave-restricted species in the ACCS and compare it with previously published hotspots in Brazil. Our list of cave-obligate fauna comprises 31 species, including 23 troglobionts and 8 stygobionts. The exceptional diversity of the ACCS can be attributed to factors related to the high dispersal potential of cave fauna within the system, high surface productivity, and the large size of the cave system size. Notably, we observed highly troglomorphic species in the ACCS, some of which are the most troglomorphic species in their respective groups in Brazil. The huge volume of galleries, high humidity, and trophic conditions prevailing in the ACCS may have played a role in shaping the strong troglomorphic traits observed in these species. However, all the obligate cave species in the ACCS require conservation attention and are at an elevated risk of extinction due to their limited ranges, few occurrences, and many potential threats. This study sheds light on the biodiversity and conservation status of cave-restricted fauna in the ACCS and highlights the importance of protecting these unique ecosystems.

Beyond Expectations: Recent Discovery of New Cave-Restricted Species Elevates the Água Clara Cave System to the Richest Hotspot of Subterranean Biodiversity in the Neotropics

“…The Água Clara Cave System (ACCS), situated in northeastern Brazil, has gained recognition as a "Hotspot of Subterranean Biodiversity" (HSB) due to its remarkable richness of cave-restricted fauna [1,2]. This cave system comprises a network of extensive subterranean conduits interconnected through one of the numerous fluvial outlets found on the eastern periphery of the Serra do Ramalho karst area in the western Bahia state.…”

“…This cave system comprises a network of extensive subterranean conduits interconnected through one of the numerous fluvial outlets found on the eastern periphery of the Serra do Ramalho karst area in the western Bahia state. The system encopasses four caves: Gruna da Água Clara (13,880 m), Gruna dos Índios (510 m), Lapa dos Peixes I (9320 m), and Lapa dos Peixes II (2100 m) [1]. It is noteworthy that the cumulative length of all caves within the Agua Clara Cave System (ACCS) stands at 25,810 m. However, when accounting for the inaccessible and unexplored areas existing between the caves, it is plausible that the system might extend to more than 27 km.…”

“…More recently, there has been a movement to raise this threshold to a minimum of 25 cave-restricted species. However, this change has faced some criticism due to concerns about the arbitrary nature of the cutoff and the necessity to consider various parameters when defining subterranean hotspots [1]. These parameters encompass the need to consider different scales when identifying hotspots, the cave's latitudinal location, the lithology associated with the cave, the level of threat to subterranean habitats, and the number of cave-restricted species exclusive to that cave (or system) relative to the total number of troglobitic/stygobitic species it supports [1].…”

“…Prior investigations conducted at the ACCS have identified a total of 31 cave-restricted species, spanning multiple taxonomic groups, including Hexapoda (9 species), Arachnida (7 species), Crustacea (6 species), Myriapoda (5 species), Gastropoda (2 species), Turbellaria (1 species), and Siluriformes (1 species) [1]. These species predominantly occupy terrestrial (22 species) habitats, with a smaller representation of semiaquatic (5 species) and aquatic species (3 species) [1]. Notably, only a fraction of this assemblage (11 species) has been formally described [12][13][14][15][16][17][18][19][20][21][22].…”

“…The recent discovery of ten additional species within the ACCS raises a red flag on two critical fronts. Firstly, it underscores the extraordinary diversity of this system, currently facing severe threats driven by an unprecedented increase in various anthropogenic impacts, particularly in recent decades [1]. Urgent actions, such as the establishment of a fully protected conservation unit, are imperative.…”