WHAT LIES BENEATH
Scientists in Slovenia are leading the charge to understand and protect a charismatic, cave-dwelling salamander – and the subterranean habitats that supply much of the region’s drinking water. KATIE JEWETT reports.
Deep under Slovenian soil, KATIE JEWETT examines the complex relationship between a healthy human population, its vulnerable water supplies – and a mysterious species of salamander.
Gregor Aljančič enters a concrete tunnel and descends into a subterranean world below the city of Kranj, in northern Slovenia. Lamps illuminate his one-minute walk down the claustrophobic passageway, which fades to pitch black as he reaches the main chamber of Tular Cave Laboratory. The 50-year-old has visited the laboratory since boyhood, when he came with his father, the lab’s founder, and he knows its occupants well. The reinforced natural cave, once a World War II air raid shelter for a factory, now serves as a safe haven for blind salamanders known as olms (Proteus anguinus). Aljančič, a cave biologist, visits every other day to ensure conditions remain comfortably dark and damp for his study subjects.
“Continuing father’s work was at first an obligation, but then it became my passion too,” he says. “Many of these animals I’ve known since before I can remember. They’re all still alive.”
Aljančič uses night-vision goggles and the dim beam of a headlamp to search pools of water for olms slung over rocks or wedged into crevices. Direct illumination disturbs the salamanders. When light strikes, their translucent skin flashes like crescent moons and they dash for darkness, swimming in exuberant wriggles beneath the limestone ledges.
Aljančič’s father, prominent cave biologist Marko Aljančič, established the lab in 1960. He built an assemblage of concrete pools, and over time filled them with olms from cave systems in southwestern Slovenia, dedicating his life to studying their cryptic behaviour. But his amphibian charges outlived him, as he came to suspect they might. Gregor Aljančič estimates that individuals could survive to be a century old, but like many other aspects of olm biology, no one knows for sure.
While Tular Cave Laboratory mainly serves researchers, everyday Slovenians are well aware of the olm’s existence. Slovenia is the birthplace of cave biology as a formal discipline, and it was here that olms were first encountered. Today, they are an attraction at Postojna Cave Park, one of the country’s most popular tourist destinations. Visitors can ride a train through the cave, which showcases the dramatic pillars and ornate chambers of the geological karst landscape that underlies a quarter of Slovenia. The highlight is coming face to face with the country’s iconic salamander: človeška ribica (tchlo-vesh’-khah Ree’-bee-tsah). The Slovenian name translates to “human fish,” but most observers don’t fully appreciate how much they share with an animal that lives its whole life in darkness.
Beneath Slovenia’s bustling cities and rolling countryside, the cave systems that have shaped and sheltered olms for millions of years are changing fast. As scientists probe for insights into olms’ mysterious existence, they’re finding that human health is closely intertwined with that of the salamanders. Across the olm’s home range, people have used the subterranean environment as both a source for drinking water and a dump for waste. Now, scientists are working to illuminate ways to safeguard the “human fish” from its namesake.
Although olms seem small, reaching just 20 to 30 centimetres in length by adulthood, they are the largest of the world’s cave-dwelling animals, and fierce apex predators. Two external gills flare into scarlet tufts at the back of their flat heads, and their four tiny limbs stick out from the far ends of their elongated bodies like pushpins. Though blind, olms have remarkably heightened senses of smell and hearing. They stalk remote cave depths for fish and tiny crustaceans, lurching forward at exactly the right moment, paddle-shaped snouts agape, to gobble prey whole. Marko Aljančič described these skilled hunters as “the mysterious rulers of karst darkness”.
Olms make their home beneath the Dinaric Alps, a mountain range that starts in Italy and runs
southeast through Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, and Albania. Karst unites the region underground. Its intricate topography forms when water enters surface fissures and percolates down through soluble rock, like limestone or dolomite, eroding larger conduits and chasms. Over millions of years, underground water ranging in force from small drips to large rivers carves a complex latticework of caves.
“Underground, the karst does not follow a clear map,” says Magdalena Năpăruş-aljančič. “It’s a network of channels that can be straight or very complex.” Born in Romania, she earned a PHD in geography with a specialty in karst, a focus that led her to Slovenia where she met and married Gregor Aljančič. Today, she’s a research fellow at Slovenia’s Karst Research Institute.
At first, Năpăruş-aljančič was interested only in the challenging, beautiful rock formations. But Aljančič opened her eyes to the challenge and beauty of karst’s creatures. She likens her first time entering Tular Cave Laboratory to “stepping into geological times, like a living Jurassic Park, since you have the opportunity to witness animals you only see in photos”.
A stream meanders through the cave lab. Overhead, stalactites have grown down from the concrete tiles, elongated mineral evidence of water’s pathways. To mark the birth of their first child last year, they flipped one of the tiles so that the growth would start anew. “We want to show our son that the stalactite is as old as he is,” says Aljančič.
Slovenians aren’t generally in such close touch with the underground, and as a result, their relationship with olms has long been marked by misconception. When villagers encountered olms in the late 17th century, after unseasonable rains flushed the salamanders into sunsplashed springs on the surface, they surmised that the pale, serpentine creatures were offspring from a fearsome dragon’s lair. In 1689, naturalist Janez Vajkard Valvasor described the olm based on these stories – fuelling Slovenia’s enduring fascination with its “baby dragons”. A formal, scientific description wouldn’t appear for another century.
Like all cave life, olms descended from surface-dwelling species. Olms and their closest living relatives, the mudpuppies or water dogs of North America, last shared a common ancestor around when the dinosaurs died off and the earliest birds began to emerge. When tectonic activity gave rise to new subterranean habitat, the olm’s ancestors eventually descended into karst. Dramatic climate shifts like the most recent ice age and aridification swept the region, wiping out many vertebrates across the present-day Dinaric Alps, but ancestors of the olm had already moved underground, serendipitously evading the worst of the weather.
Gregor Aljančič estimates that individuals could survive to be a century old, but like many other aspects of olm biology, no one knows for sure
“Evolution took the same path every time an olm ancestor went underground – they lost contact, all relation to one another – but despite this isolation they all came out the same,” says Rok Kostanjšek, a molecular biologist and professor at the University of Ljubljana in Slovenia’s capital city. His team hopes to resolve whether the olm is actually seven, or perhaps nine, separate species, currently lumped into one due to morphological similarities and lack of definitive data. Each population is endemic, sometimes living entirely within a single well hole, and each one likely arose from an independent evolutionary event. This phenomenon, known as parallel evolution, happens when separate lineages evolve in the same way – mirroring one another in form – since they’re responding to similar environmental pressures.
The trying conditions of caves shaped an array of adaptations that seem like the stuff of science fiction. Special skin receptors help olms sense Earth’s magnetic field and changes in the electrical fields of other organisms. In the dark depths, vision serves little purpose, so by adulthood, the clear eyes that olms are born with have nearly disappeared beneath layers of skin, though they can still sense light. Olms have also mastered the art of doing nothing, weathering years without moving or eating, with negligible physiological consequences. In January 2020, scientists
announced that a wild olm they had been monitoring remained stationary for seven years before stirring.
Despite all that scientists have learned about the creatures’ life history through the years, mysteries still abound. No one knows where wild olms reliably live or how many there are, which makes it hard to advocate for protected areas. The International Union for Conservation of Nature (IUCN) classifies the olm only as Vulnerable, because there isn’t enough data to say definitively whether it is endangered. “These animals have been known for almost three centuries, yet we hardly know anything about natural populations,” Kostanjšek says. Traditional population monitoring techniques, like annual counts, don’t work when the animal being tracked lives beyond reach. If different olm populations indeed represent different species, as Kostanjšek and other scientists suspect, then each is far more endangered than presently supposed.
That’s a problem, because most Slovenians confuse olms’ inaccessibility with immunity to human impact, says Năpăruş-aljančič. “They think if something is underground it’s safe.”
In the summer of 1983, karst researchers sampled an inconspicuous-looking spring. The spring surfaces below a limestone wall, and serves as the sole source for the Krupa River, which meanders only 2.5 kilometres through the lush Bela Krajina region of southeast Slovenia. They hoped to confirm that the spring could supply drinking water to nearby villages. Instead, they found it was laced with dangerous levels of cancer-causing polychlorinated biphenyls, or PCBS. It was just the latest example of fallout from one of the worst environmental disasters in the nation’s history. For two decades prior, a nearby capacitor factory had disposed of its PCB waste in karst sinkholes. Over time, these contaminants filtered down through soil until they hit impermeable rock – where groundwater collects and olms live – polluting the spring that feeds the Krupa River. Slovenia stopped using PCBS in 1985, but the Krupa River remains laced with the toxins.
Similar tales are common across southeastern Europe, where many communities use the groundwater within karst formations. In Slovenia, for