The effort matters because subterranean ecosystems are among the most difficult environments on the planet to study. Caves, wells, and aquifers are physically inaccessible to most sampling methods, and the animals that live in them are small, pale, often eyeless, and exquisitely adapted to perpetual darkness. Traditional biodiversity assessments struggle in these conditions, and even when studies are completed, the resulting data frequently end up locked in personal notes or project-specific formats that cannot be combined with modern databases. The researchers behind the new compilation, led by Sarah Boulamail and colleagues working within the STIGE-CLIMAQUIFERI project, set out to reawaken this dormant data by reorganising everything according to the Darwin Core standard, the shared vocabulary that allows biodiversity records from different eras and different observers to speak the same language.

Apulia is a natural laboratory for this kind of work. The region’s karst landscape covers roughly 8,600 square kilometres and contains more than 2,300 natural caves, carved over millions of years into soluble Cretaceous limestone. Rainwater that falls on the Murge Plateau or the Gargano promontory largely vanishes underground, draining through fractures and sinkholes into extensive aquifers rather than flowing across the surface. The region is divided into six hydrogeological units, including the Salento peninsula, which is bordered by the sea on both sides, a geography that has repeatedly exposed its groundwater to marine influence. The Alta Murgia Regional Park, protecting a large part of the corresponding aquifer, was designated Italy’s twelfth UNESCO Geopark in September 2024, underlining how much scientific and cultural value rests on these underground systems.

That geography has produced a fauna with deep historical roots. Apulia’s stygofauna, the aquatic animals of its groundwater, includes palaeomediterranean relicts that colonised the region during the Tethys period, when ancient seas connected the basins of the Mediterranean. Genera such as Metahadzia, Monodella, Spelaeomysis, Stygiomysis, and the predatory shrimp Typhlocaris represent some of the oldest and most significant components of Italian groundwater fauna. Repeated marine transgressions and regressions over geological time isolated and reshaped these populations, producing a high proportion of ancient, specialised, and rare species. The terrestrial side is less diverse, likely because those same marine floods repeatedly reset the distribution of land animals, but it still holds remarkable endemics such as the cave beetle Italodytes stammeri, the pseudoscorpion Hadoblothrus gigas, and the springtail Troglopedetes ruffoi.

Assembling the dataset required combing through 61 publications, from the pioneering work of Caroli and Stammer in the 1920s and 1930s, through Sandro Ruffo’s surveys of the 1940s, to Gian Luigi Pesce’s extensive investigations from the 1970s onward. The most influential individual sources were Pesce and colleagues’ 1978 study, contributing 206 records, and Karanovic and Pesce’s 2001 work on copepods, contributing 134. Crucially, the compilation also folds in 63 records of unpublished observations validated by Salvatore Inguscio and other amateur biospeleologists, a community whose field expertise has long outpaced the formal literature. The ongoing STIGE-CLIMAQUIFERI project added 27 novel records and multiple recent confirmations of historical sites, collected with hand-operated 0.5-millimetre nets and cylindrical traps baited with fish or meat, with specimens fixed in ethanol and identified under stereomicroscopes.

The numbers reveal both the richness and the unevenness of what is known. Stygobionts, species fully committed to groundwater life, make up 30 percent of the 82 aquatic species recorded, while troglobionts account for 60 percent of the 27 terrestrial species. Arthropods dominate the records, led by copepods with 50 species, malacostracans with 19, and ostracods with 6, alongside 11 species of arachnids among the terrestrial fauna. The most frequently recorded aquatic species are the mysid shrimp Spelaeomysis bottazzii and the isopod Proasellus banyulensis, each with 57 records, and the copepod Eucyclops serrulatus with 52. Among the largest European groundwater animals, the decapod Typhlocaris salentina, a blind predatory shrimp that can grow to several centimetres, appears in 17 records. One record stands out entirely: the stygobitic sponge Higginsia ciccaresi, found in the Zinzulusa caves, a rare example of a sponge adapted to anchialine cave waters.

Geographically, the dataset is heavily lopsided. The Salento unit alone accounts for 481 of the 622 records and 87 of the 109 species, a product of both genuinely higher biodiversity and far more intense research activity. The Murge Plateau follows with 66 records and 27 species, Gargano with 41 records and 23 species, and the Tavoliere with 24 records and 12 species. Two entire hydrogeological units, the Brindisi Plain and the Ionian Arch of Taranto, have no observations at all. The single richest sites are the caves Zinzulusa, with 27 species, and L’Abisso, with 22, plus the drainage tunnel Fonti di Carlomagno with 18, all in Salento. The municipality of Castro, home to both Zinzulusa and L’Abisso, emerges as one of the richest European localities for stygofauna, with 40 reported species occurrences.

That imbalance is itself a scientific finding. Although the data are not sufficient to fit a species accumulation curve, the high ratio between sampling effort and observed species suggests that the under-sampled areas could harbour biodiversity comparable to the well-studied ones. In other words, the blank spaces on the map may not be empty; they may simply be unexplored. The temporal picture raises a parallel concern. Most records date from the 1970s and 1990s, and only 12 percent of the historical presence data have been confirmed by recent investigations between 2020 and 2024. Those recent checks did confirm the continued presence of flagship species such as Spelaeomysis bottazzii and Typhlocaris salentina at various historical sites, and they revealed impressive richness at L’Abisso, though only a portion of the species recorded there in the past reappeared. The limited sampling effort so far cannot determine whether subterranean richness has genuinely declined.

The stakes of that question are rising. Southern Apulia hosts some of Europe’s southernmost major aquifers, and its groundwater temperatures are relatively high, making the system potentially vulnerable to global warming. The region’s groundwaters face chemical stress from salinisation, driven by extensive connection with marine waters, increasing aridity, changing land use, and often uncontrolled extraction. Because many of the recorded species are narrow endemics with tiny ranges, a single degraded aquifer could erase a species entirely. The dataset’s records of physical and chemical parameters at collection sites, where available from the original publications, provide a baseline against which future change can be measured, which is precisely why the authors argue that a comprehensive new sampling campaign across the whole territory is needed.

The compilation also carries a methodological caveat with real scientific upside. Every identification, historical and recent, rests on morphological characteristics, and the specimens in the older literature have not been reanalysed. Cryptic species, genetically distinct but visually identical, cannot be ruled out, meaning the true diversity of Apulian groundwater may be even higher than the 109 recorded species. Modern genetic tools applied to preserved and freshly collected material could reveal hidden evolutionary lineages. Meanwhile, the dataset itself, released under a CC0 public domain licence and archived on Zenodo with metadata following the Ecological Metadata Language standard, is designed to keep growing through the STIGE-CLIMAQUIFERI project and to be shared through the LifeWatch Italy data portal. What began as a rescue mission for scattered notes has become the foundation for studying and conserving one of Europe’s most distinctive underground faunas, and a demonstration that decades of amateur expertise and dormant publications can be turned into a living scientific resource.

Subject of Research: Compiling a standardised 93-year dataset of subterranean fauna in the Apulia region of southern Italy

Article Title: Integrating formal surveys and local knowledge: Insights into the subterranean fauna of Apulia

Article References: Boulamail, S., Inguscio, S., Ventruti, S., Barzaghi, B., Brognoli, D., De Giorgi, R., Langeneck, J., Lo Parrino, E., Mancini, E., Manenti, R., Martínez, A., Pulieri, M., Rossi, E., & Cozzoli, F. (2025). Integrating formal surveys and local knowledge: Insights into the subterranean fauna of Apulia. Subterranean Biology, 52, 29-44. https://doi.org/10.3897/subtbiol.52.140693

Image Credits: AI Generated

DOI: 10.3897/subtbiol.52.140693

Keywords: stygofauna, troglobionts, Apulia, karst, groundwater biodiversity, Subterranean Biology, endemic species, Darwin Core, cave biology, aquifer conservation, Salento, biodiversity dataset