A Hotspot of Subterranean Biodiversity on the Brink: Mo So Cave and the Hon Chong Karst of Vietnam

Abstract

The southern part of the Mekong Delta Limestones of Vietnam (MDL-HC or Hon Chong karst) comprises numerous small limestone hills. It is a hotspot of biodiversity for soil and cave invertebrates. Here, we synthesize the results of biological surveys carried out in Hang Mo So, the richest MDL-HC cave for troglobionts, and in surrounding karsts. Methodologies for the ecological characterization of species are discussed, with emphasis on parallel sampling (external soil plus cave). Hang Mo So has 27 troglobionts, including many still undescribed. An additional 40 cave-obligate species are known from other caves of MDL-HC. Among them, several are expected to be found in Hang Mo So. Most troglobionts of MDL-HC are endemic. Several relictual taxa without close relatives in Southeast Asia occur in Hang Mo So and in MDL-HC, reflecting an ancient origin of the fauna. The reasons for this richness are uncertain, but the cause of its current destruction—quarrying—is all too evident. Most of the original 4 km2 of the MDL-HC karst has been destroyed or soon will be, ultimately leaving only 1.6 km2 unquarried. Endemic species linked to karst habitats are, therefore, under clear threat of extinction. The Hon Chong karst (MDL-HC) was listed among the ten most endangered karsts on the planet 25 years ago. Today it would probably top the list.

Global Subterranean Biodiversity: A Unique Pattern

“…Lukić et al [36] reported that almost all information for the fauna of the Lukina Jama-Trojama Cave System in Croatia dates from the 1990s or later. The same is true for Fern Cave in Alabama [44], Hon Chong in Vietnam [46], and the Água Clara Cave System in Brazil [27,28]. Sampling effort is therefore a major determinant of the richness of species in these caves.…”

“…Deharveng et al [46] employed a decision system to determine if a species was troglobiotic in their analysis of Vietnamese caves. These caves are usually short and shallow, with frequent terrestrial and aquatic connections to the exterior, allowing constant inputs of nutrients.…”

“…Their vulnerability is dependent on the size and isolation of karst or hydrogeological units available for the cave-restricted fauna. In this regard, tropical tower karsts with hills scattered on non-limestone terrain are especially vulnerable to local limestone exploitation [46,151]. Additionally, cave-restricted species are vulnerable to a variety of environmental perturbations, at an extent that is unknown in most cases.…”

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

“…Most of the HSBs are situated in temperate regions, with only a smaller portion located in sub-tropical or tropical areas [4][5][6][7][8][9][10][11]. Additionally, it is noteworthy that most HSBs within these sub-tropical and tropical regions have only recently come to the forefront, signifying an upsurge in cave fauna research in these regions.…”