Interstitial fauna of the Sava River in Eastern Slovenia

Abstract

Interstitial water that occupies the pore spaces within unconsolidated sediments is a unique habitat, inhabited by surface as well as exclusively subterranean species (stygobionts). The best studied of all interstitial habitats is the hyporheic zone, an interface between surface water and groundwater (phreatic zone) environments. The Sava River in central Slovenia (i.e., at the Ljubljana alluvial plain) readily qualifies as one of the global hotspots of interstitial biodiversity, while data from other river sections are lacking. In 2015, we sampled two gravel bars on the final Slovenian section of the river (Eastern Slovenia), and collected nine samples per site using the Bou-Rouch pumping method. At »Čatež ob Savi« and »Obrežje« sites, at least 26 invertebrate species with 14 stygobionts and 25 invertebrate species with 13 stygobionts were identified, respectively. Altogether, 33 invertebrate taxa with 16 stygobionts were recorded, which increased the previously known interstitial stygobiotic richness of the Sava River in Slovenia by eight species (to 37 species). Three species of the stygobiotic amphipod genus Niphargus were recorded in Slovenia for the first time, one of which is even a new species to science. We discuss the novel results in the context of current national conservation practices.Intersticijska voda – voda med zrni nesprijetega sedimenta, je edinstven življenjski prostor tako za površinske kot tudi izključno podzemne vrste (stigobionte). Najbolje raziskan med plitvimi intersticijskimi habitati je hiporeik, prehodni pas med površinsko vodo in globoko podtalnico (freatikom). Odsek reke Save na območju Ljubljanskega polja (osrednja Slovenija) sodi med svetovne vroče točke intersticijske vrstne pestrosti, medtem ko podatkov iz drugih odsekov reke skoraj ni. Leta 2015 smo z metodo Bou-Rouch pridobili po devet vzorcev iz vsakega od dveh prodišč v končnem odseku Save (vzhodna Slovenija). Na prodiščih »Čatež ob Savi« in »Obrežje« smo zabeležili najmanj 26 oz. 25 nevretenčarskih vrst, od tega 14 oz. 13 stigobiotskih. Skupno število najdenih taksonov, t.j. 33 nevretenčarskih, od tega 16 stigobiotskih vrst, je zvišalo pestrost savskih stigobiontov za osem vrst (na 37 vrst). Tri vrste iz rodu slepih postranic (Niphargus) smo v Sloveniji zabeležili prvič, od tega je ena nova za znanost. V prispevku izsledke obravnavamo v luči trenutne naravovarstvene prakse.