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Could you conduct your research from the bottom of a subterranean lake? This is the reality for scientists who wish to find out all they can about the remarkable cave-dwelling wildlife of Bosnia & Herzegovina – before it’s too late

Read the article in Serbo-Croatian here Članak na srpsko-hrvatskom jeziku pročitajte ovdje

Pale and slender with fine, fringed gills, you could be forgiven for thinking that the Olm Proteus anguinus came from another world entirely. And in a way, you’d be right. This rare freshwater salamander is eyeless, devoid of pigment and possesses only the smallest, most delicate of limbs. To us humans, it can seem like there is something missing. But in reality, it is perfectly adapted for life in subterranean caves beneath the Dinarides mountains in the Balkans, Europe. In fact, the Olm is found nowhere else on earth. With a heightened sense of smell and hearing, the ability to resist long-term starvation and even a newly discovered sensory organ that detects the electric fields of other animals, it has everything it needs to survive in this secluded environment.

Like its occupants, the limestone caves of the Dinarides are truly exceptional. In some places, vast stalactites and stalagmites create stunning, cathedral-like formations, while other areas preserve fossils from former millennia. This is the location where naturalists discovered cave-dwelling animals for the first time, creating a whole new branch of biology. The Olm and its fellow cave-dwellers may be perfectly suited to life underground here, but the humans that wish to study them are not. To discover more about the unique wildlife that inhabits these limestone caverns, modern researchers need to be cavers, divers and fishers all at once. But why go to all this trouble?

The reason is an urgent one: we need to discover all we can about this remarkable ecosystem before it is lost forever. The Balkans’ last remaining wild waterways are threatened by proposals for dams, hydropower projects and many other modifications. “Building dams is disastrous for the very sensitive organisms that inhabit places with such specific conditions,” says Marijana Demajo, BPSSS (BirdLife Serbia), Balkans Small Grants Co-ordinator for Critical Ecosystem Partnership Fund (CEPF) Mediterranean*. “Underground life depends on the water level; it’s fed from the surface watercourses.”

The Olm is nicknamed the “Human Fish” due to its fleshy skin colour © Gregor Aljančič, Tular Cave Laboratory
The fate of cave-dwelling wildlife depends on the condition of waterways above ground © Jasminko Mulaomerović / CKS

For example, when the Trebišnjica River was enclosed in artificial concrete channels in Bosnia & Herzegovina, it cut off the natural flood water that usually reached sink holes at the edges of the Popovo Polje plains. As a result, large colonies of exclusively cave-dwelling tube worms were completely killed off within the sink holes. Fortunately, the more we know about an ecosystem, the more information we have to make positive change to policy. And so CEPF brought together experts from the Subterranean Biology Lab at the University of Ljubljana, Slovenia, and the Center for Karst and Speleology, based in Bosnia & Herzegovina. Together they formed the SubBio Code project. Their mission: to develop new tools to identify and catalogue the rich underground biodiversity of the Dinarides region in Bosnia & Herzegovina.

“This a landscape full of life, not some lifeless place. The discovery of new species is important in order to demonstrate the true value of karst [limestone] landscapes, and to show that they are not just geomorphological formations, but a living system,” asserts Demajo. “And let us not forget the importance of educating the local community.”

This March, researchers braved freezing snow and flooded caverns (and multiple COVID tests) as they ventured back out into the field to survey this little-known network of caves. Over just a few days, they advanced the knowledge of the habitat and its wildlife further than ever before. One day, researchers were sampling springs for shrimp-like amphipod crustaceans when they met local people who, surprisingly, knew about the shrimps’ existence and had given them the name šmugarica. Later the same day, they dispelled a false rumour about the cave Ratkovića Pečina, which was thought to stretch far back into the hills but turned out to be of normal dimensions. Towards the end of their visit, a local caver showed them a cavern full of bats whose guano provides nutrients for a thriving ecosystem of invertebrates. The team used their abseiling and rock-climbing experience to survey the area vertically and visit three caves in the side of Korita hill.

Rock climbing is just one of the practical skills that team members have acquired as part of the project’s mission to train and educate scientists, students, volunteers and the local community in the research and conservation of these caves. As well as netting creatures directly from the water, the team also uses an exciting new technique using eDNA (a shortening of ‘environmental DNA’), developed by a previous CEPF-funded project as a way to detect the presence of Olms without capturing and disturbing them. eDNA is the genetic material that gets released by animals as they go about their lives – in the form of skin, mucous, faeces and many other kinds of fragments. Scientists are able to detect this material in the water and identify which species it belongs to, helping them to map its distribution and make conservation plans.

As fascinating as this is, no part of their research is as nail-biting as underground diving. Croatian biologist and cave-diver Dušan Jelić, who discovered the largest known population of Olms in his native country, explains what it’s like to put on full scuba gear and venture beneath the surface of the water to observe first-hand the creatures that inhabit the gloomy depths. “It is an amazing experience to see something that only a few people in the world have seen before you – or occasionally, to be the first person ever to see it. Sometimes it can be scary, just to be underwater, in a small space, isolated from the rest of the world … but mostly it is a wonderful feeling.”

It is a rare privilege to venture into the realm of the Olm, however fleetingly. And though these creatures are perfectly at home in the dark, by shining a light on them we can secure lasting safety for the unique and beautiful world that lies beneath our feet.

“It is an amazing experience to see something that only a few people in the world have seen before you – or occasionally, to be the first person ever to see it.”

Dušan Jelić, Croatian biologist and cave diver

Ground-breaking research into rare cave-dwelling fish

Southern Dalmatian Minnow © Dušan Jelić

In 2020, another exciting new project by the Croatian Biological Research Society set out to investigate the Southern Dalmatian Minnow Delminichths ghetaldii – a rare freshwater fish found only in southern Bosnia & Herzegovina and Croatia. Although the species is already known to use caves, this project could confirm its status as Europe’s first exclusively cave-dwelling fish. During September and November, researchers surveyed 19 caves through fishing and cave diving, and consulted experts from Croatia and France to set up eDNA methods. They are also laying the foundations for a conservation plan for the species, and forming a network of experts and decision-makers through which to share knowledge.

“We’re working on a rare fish, so it’s really amazing when you actually find it – especially in large numbers, or in places where you don’t expect it to be present,” says project co-ordinator Matej Vucić. “It’s a really good feeling to know there is still hope to save something you’re working on – but only if everyone acts quickly and seriously.”

“It’s a really good feeling to know there is still hope to save something you’re working on – but only if everyone acts quickly and seriously.”

Matej Vucić, project coordinator

New freshwater snail species discovered

New to science: 6. Bythiospeum dervovici, 7. Belgrandiella bajraktarevici, Belgrandiella kurtovici, and 10. Islamia buturovici

The Center for Karst and Speleology discovered five species of snail never before seen in Bosnia & Herzegovina, as part of a project to survey the country’s freshwater snail populations and the water quality of its limestone rivers and springs. In an exciting turn of events, four of the snails were completely new to science. One of the snail species was discovered during a field trip as part of a student workshop, showing that training new researchers can sometimes pay off instantly!

More worryingly, the team also found species of invasive freshwater molluscs, including the limpet Ferrissia californica, which had come all the way from North America. The next step will be to define the conservation status of the native snails on the IUCN Red List of Threatened Species.

CEPF logo

*The Critical Ecosystem Partnership Fund (CEPF) is a joint initiative of l’Agence Française de Développement, Conservation International, the European Union, the Global Environment Facility, the Government of Japan, and the World Bank. Additional funding has been provided by the MAVA Foundation. A fundamental goal is to ensure civil society is engaged in biodiversity conservation.

CEPF is more than just a funding providerA dedicated Regional Implementation Team (RIT) (expert officers on the ground) guide funding to the most important areas and to even the smallest of organisations; building civil society capacities, improving conservation outcomes, strengthening networks and sharing best practices. In the Mediterranean Basin Biodiversity Hotspot, the RIT is entrusted to BirdLife International and its Partners: LPO (BirdLife France), DOPPS (BirdLife Slovenia) and BPSSS (BirdLife Serbia).Find out more at

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