Planinska jama, Slovenia
At the southern edge of Planinsko Polje, one of the largest karst poljes located in southwestern Slovenia, lies a globally exceptional site for subterranean biodiversity, Planinska jama (Planina Cave). The cave is part of the much larger Postojna-Planina Cave System, which comprises many interconnected caves with a cumulative passage length exceeding 34 km. The system is home to 116 troglobiotic animal species and troglobiotic populations, making it the species-richest site for troglobionts in the world. It is home to the biggest troglobiotic amphibian, the olm Proteus anguinus, as well as to the only cave dwelling cnidarian in the world, Velkovrhia enigmatica. The system is also the site of the first scientific descriptions of cave animals, beginning with the discovery of the cave beetle Leptodirus hochenwartii in the first half of the 19th century. This started the research of subterranean life, and it is therefore considered a “cradle of speleobiology”. Parts of the system, especially Postojnska jama (Postojna Cave), have been visited by tourists since 1818. Postojnska jama marks the upstream entrance of the system, where the Pivka River sinks underground, while Planinska jama represents its downstream end.
In Planinska jama, the Pivka River is joined by Rak River at the largest known and accessible underground river confluence in Europe; from this point, the combined flow continues as the Unica River for approximately 500 m before emerging beneath an impressive ~65 m high vertical rock face at the cave entrance.
Although both channels of Planinska jama host numerous olms and a very rich aquatic troglobiotic fauna, the Pivka channel is more easily accessible, and can be accessed directly for nearly 2 km along its subterranean stream.
Cave waters were sampled for eDNA also few months earlier, within EU Biodiversa+ project Sub-BioMon (https://www.sub-biomon.net/) which may enable interesting comparisons with GreG outcomes.
Water sampling at the Pivka river channel in the cave.
Words by Dren Dolničar, Grega Benko & Maja Zagmajster
Photos by Grega Benko
Sampling team: Grega Benko, Nina Srečnik Lapanja, Sofia Pieri