Hidden Biological Treasures: Launching the First Studies of Endemic Molluscs in the Subterranean Ecosystems of Montsant Natural Park

With the support of Montsant Natural Park and the Department of Climate Action, Food and Rural Agenda, BioSciCat has undertaken the first studies aimed at investigating the threatened subterranean species of Montsant Natural Park. These pioneering efforts will provide essential information for the development of a future conservation strategy to safeguard these protected species and their unique underground habitats.

The Origin of It All: An Unexpected and Exceptional Discovery

Aquatic ecosystems are experiencing the greatest known loss of biodiversity worldwide. Among them, subterranean and crenic fauna—species inhabiting groundwater systems, springs and natural seepages—remain some of the least studied, yet they are remarkably rich in endemic species and particularly vulnerable to environmental change.

In recent years, biological survey work (Alba et al., 2009; Corbella et al., 2009), involving the analysis of sediments originating from groundwater aquifers and discharged through a natural spring in the Montsant mountain range (Font de la Pastera, Tarragona), led to the description of three snail species previously unknown to science (Moitessieria pasterae, M. prioratensis and Guadiella ballesterosi). In addition, specimens of a fourth species (M. seminiana), previously known from only a single locality, were identified. This finding must be regarded as truly exceptional and suggested that the subterranean aquatic ecosystems of the Montsant range could represent a hotspot of stygobiont fauna—organisms that inhabit water-saturated underground interstitial environments.

Understanding to Conserve

These organisms belong to two families of molluscs (Moitessieriidae and Hydrobiidae) whose biology and autoecology—the habitats they occupy and their ecological requirements—remain largely unknown. Available evidence suggests that some species may be endemic to a single aquifer or even to a specific sector within an aquifer system.

As a result, these molluscs are not only of outstanding biological importance but are also considered highly vulnerable to any form of disturbance, whether natural, such as prolonged droughts, or anthropogenic, including chemical pollution, groundwater overexploitation and climate change.

In recognition of this vulnerability, all four species were included in the Catalogue of Threatened Native Wildlife of Catalonia. Two species (M. pasterae and M. seminiana) were listed as Endangered, while the remaining two (M. prioratensis and Guadiella ballesterosi) were classified as Vulnerable. This designation not only grants them legal protection but also requires the environmental administration of the Government of Catalonia to develop conservation strategies aimed either at improving the conservation status of their populations or at implementing preventive management and protection measures, depending on the level of threat faced by each species.

However, designing such strategies—which must ultimately be formalised through Recovery Plans and Conservation Plans—remains extremely challenging given the profound lack of knowledge regarding the true distribution of these species, a key factor in assessing their vulnerability, as well as their biology, ecology and the pressures affecting them.

Indeed, fourteen years after their original discovery, none of the four species had been recorded again. Font de la Pastera remained the only known locality in the world for three of these species, all endemic to the Montsant massif.

Faced with this situation, BioSciCat designed and proposed a research programme to the Government of Catalonia aimed at improving understanding of the actual conservation status and vulnerability of these species, which largely depends on their distribution—still largely unknown at the time.

The First Studies

With the support of Montsant Natural Park and the Department of Climate Action, Food and Rural Agenda, BioSciCat carried out the first dedicated studies between January and June 2024 to advance knowledge of the four currently protected mollusc species inhabiting the subterranean ecosystems of the Montsant range.

The project also benefited from the participation of specialist taxonomists from the Catalan Malacological Association, Sergio Quiñonero and Joaquín Soriano, whose expertise contributed significantly to the identification and assessment of the species studied.

The biological survey and habitat characterisation programme was designed to improve understanding of the distribution of the target mollusc species, identify their populations, characterise the hydrochemical environments in which they occur, and explore their spatial patterns in relation to the aquifer compartments that have driven their speciation and currently shape their distribution.

To achieve these objectives, an extensive biological survey programme was carried out across the entire spring system of the Montsant mountain range. A total of 37 springs and groundwater discharge points considered of particular interest were investigated and sampled. The hydrological functioning and hydrogeomorphological characteristics of each spring were analysed in order to determine the most appropriate sampling strategy. Multiple sediment samples transported by emerging groundwater flows were collected and subsequently processed and examined in the laboratory by specialist taxonomists using a range of analytical techniques.

In parallel, the Montsant massif was studied from a hydrogeological perspective through the compilation and review of all available geological and hydrochemical information. This work was complemented by new physicochemical analyses of the sampled springs, providing a more comprehensive understanding of the environmental conditions governing these unique subterranean ecosystems.

Unexpected Results and Unimaginable Treasures

The work carried out has greatly expanded our knowledge of the four target species, particularly regarding their distribution—information of critical importance for the development of the conservation strategy that will need to be implemented in the coming years.

On the one hand, the survey of the stygobiont malacofauna inhabiting the Montsant aquifers, although intensive and highly successful in revealing the existence of a remarkably rich community, failed to detect any additional populations of Moitessieria pasterae. Nevertheless, the species was rediscovered at the spring where it was originally described. While this finding does not rule out the existence of further populations, it highlights the need for precautionary conservation measures. Indeed, it remains plausible that the species is restricted to a very limited sector of the mountain range’s groundwater bodies, making it exceptionally vulnerable to environmental disturbance.

In contrast, Guadiella ballesterosi was recorded at seven different localities. This discovery suggests the existence of multiple populations and confirms that the species is widely distributed throughout the hydrogeological system influenced by the Montsant massif. This is encouraging news, indicating a greater degree of demographic and ecological resilience than could previously be inferred from the single locality from which the species was originally known.

The findings concerning M. prioratensis and M. seminiana revealed a strikingly similar—and potentially coincident—disjunct distribution pattern. Both species appear to be restricted

to two geographically distant sectors, while being absent from the remainder of the mountain range’s spring systems. If confirmed, this unusual distribution could provide valuable insights into the internal structure and functioning of the region’s hydrogeological framework. In any case, the results allow for a more optimistic outlook regarding the long-term conservation prospects of both taxa, although their vulnerability remains a matter of concern.

Finally, we must highlight what may represent the most unexpected and extraordinary outcome of the study. Biological surveys identified a total of fifteen species of stygobiont snails within the study area, nine of which appear, following preliminary laboratory analyses, to be new to science and are currently undergoing detailed taxonomic investigation.

This level of species richness is unprecedented and establishes the Montsant subterranean ecosystem as the most important known hotspot of stygobiont organisms—and, consequently, of endemic biodiversity—in the Iberian Peninsula. The density of presumed endemic taxa confined to the massif is truly exceptional and far exceeds what has been documented elsewhere in the region.

The fissured and granular aquifers of the Montsant range appear to have provided an extraordinary hydrogeological setting for the speciation of moitessieriid and hydrobiid molluscs. In light of the present study, these subterranean ecosystems emerge as a biological treasure of exceptional importance, unparalleled within our biogeographical context.

Funding and Support

We would like to acknowledge that this research was made possible through the support and funding provided by the Government of Catalonia and the European Union.

Funding was awarded under Resolution ACC/2615/2023, a grant programme aimed at supporting the management of Catalonia’s protected natural areas and the conservation of threatened habitats and species within the framework of the Rural Development Programme of Catalonia 2014–2022. The project was co-financed by the European Union through the European Agricultural Fund for Rural Development (EAFRD) (43%) and by the Department of Climate Action, Food and Rural Agenda (57%).

The studies and fieldwork described here would not have been possible without the technical and logistical support provided by Montsant Natural Park, particularly Ricardo Collado, Josep Maria Blanch and David Iturria.