Early in November last year, Lara Drazenovic was cleaning out her flooded cellar in the small Slovenian village of Kompolje when she made a curious discovery: swimming in the murky water around her feet was a pale, snake-like creature, about the length of a ruler. The local name for the strange animal Drazenovic had stumbled upon is 'človeška ribica'. The English translation? 'Human fish'.
As evocative as that moniker is of the creature's pale, flesh-like skin, it is also misleading, since the 'human fish' is not a fish at all, but rather a rare and increasingly threatened amphibian. Known more commonly as the olm, or (less cryptically) as the blind European cave salamander, it is the continent's only cave-dwelling vertebrate – one whose covert, aquatic lifestyle scientists know little about.
Like some other creatures who live out their lives in the dark, olms (Proteus anguinus) have little use for eyes, so theirs never fully develop – but they're compensated for the loss with a keen sense of smell and hearing, as well as a few more enigmatic faculties, like the ability to sense electricity and possibly even magnetic and electrical fields, which comes in pretty handy as the olms twist their way through the water hunting snails and small crabs. And – just like everyone's favourite Peter Pan animal, the axolotl – the olm never quite grows up, retaining its larval attributes (like its bright external gills) into adulthood. As for old age, that sets in only much, much later – olm lifespans can surpass 100 years.
The natural habitat of the species is the vast network of water-filled caverns that form part of the Dinaric Karst, an underground system that stretches from eastern Italy, through Slovenia and on down into Albania. The ins and outs of the olm's subterranean life here are still a mystery to researchers, mostly because it's incredibly tricky to study such a small creature in a landscape that's difficult, and in many places impossible, for humans to access.
In fact, until fairly recently, the only way for us to make contact with the karst's flagship species was during an encounter much like Lara Drazenovic's. The karst ecosystem relies on seasonal flooding, the surging waters trafficking organic matter and freighting its many tiny inhabitants from place to place. For the olms, this occasional upheaval can spell trouble. While researchers suspect the salamanders have evolved strategies for bracing themselves against the watery onslaught, the floods still carry a few casualties away with them, depositing the olms far from home, in water-logged fields or inundated basements, where humans can find them. It's likely that our earliest encounters with these strange creatures, and our first descriptions of them, were the result of such events. The olm might in fact be the first cave animal to ever be scientifically described (early descriptions exist from as far back as 1689) and, particularly in Slovenia, the animals have slithered their way deep into scientists' hearts.
Still, there are not too many people who know exactly what to do with a washed-out olm. And when word of Drazenovic's cellar discovery got out, there was one person uniquely qualified to deal with the amphibian castaway: Gregor Aljancic, the head of Slovenia's Tular Cave Laboratory. Situated in a natural cave on the outskirts of the city of Kranj, it's one of only two laboratories in the world that specialise in studying the salamanders, and breeding them successfully outside of their natural karst habitat. "Our mission is to preserve the species for the future [and] to uncover [its] largely unknown subterranean life [and] its amazing adaptations to the cave habitat," says Aljancic.
Olms have been happily ensconced in the lab since the 1960s (and most of the pioneering olm settlers are still alive!), but in more recent years Aljancic's lab has also become something of a salamander sanctuary. Since 2008, the team has been focusing on the phenomenon of 'olm washout', dealing with over 30 cases of injured and marooned olms around the country – they've successfully returned 15 of the casualties to their source populations. So Aljancic was well prepared to deal with the November rescue mission.
"Along with my wife Magdalena Naparus-Aljancic, a karstologist, we arrived to the site within an hour, and found the animal being well taken care of, already [being] admired by a big group of residents and two TV teams who happened to be in the area at that time," he says of his latest rescue.
The animal, thought to be around 25 years old, was carefully examined and photographed, and a skin swab was taken to provide the team with a DNA sample. The olm was lucky: its aboveground misadventure didn't cause any injuries and a checkup with a veterinarian found it was in good condition. But Aljancic is worried about future olm casualties, especially as climate change threatens to make flooding events more frequent and intense.
Listed as 'Vulnerable' by the IUCN, the species faces other threats too, including disturbances caused by engineering works and groundwater pollution. The salamanders are uniquely adapted to the conditions of their subterranean home, and even subtle ecological changes can affect them. Populations in some areas have already become extinct. "Groundwater is the only reliable source of drinking water in karst regions around the world. In Slovenia, around half of the drinking water comes from the olm's habitat. The olm is therefore a critical indicator species of groundwater purity, and as such its study is of paramount importance to public health and everyday life," Aljancic adds.
For Aljancic and his team, the first step in helping to preserve the species has been figuring out how to trace and monitor surviving populations in their inaccessible cave habitats. Their solution? Sleuthing for traces of olm DNA in water.
"We have developed and successfully tested a novel forensic method to detect traces of DNA released into the environment. During the process of skin regeneration, fragments of epidermal cells, along with the DNA they contain, are constantly shed from aquatic animals like the olm and carried away by water. This DNA dissolved in water is called environmental DNA (or eDNA), and we can trace it simply by filtering water samples from springs and caves," Aljancic explains.
Tracking this eDNA will help the scientists pinpoint areas where olm populations are most vulnerable and therefore in need of protection. But it will also come in handy when washed-out olms need to be released back into their subterranean homes. By providing data about the distribution of different olm populations underground, eDNA can help scientists identify where a lost olm comes from, and guide its return to its rightful (source) population.
"We are aware that this initiative alone may not preserve this globally threatened species in future. However, it is of utmost importance to show to the public that even a small and underfunded NGO can achieve significant impact," Aljancic says.
And for the olm found in Lara Drazenovic's cellar, Aljancic's efforts made all the difference. "The animal was safely released back to its aquatic cave habitat – and with a bit of luck, it may live there for 80 more years," he says.
Top header image: Leonardo, Flickr
Oceans
Reproduction
Animal Behaviour
