In spring 2015 we sampled invertebrates of the Sava River interstitial from twelve
gravel bars between Medvode and the Croatian border. We used the Bou-Rouch pump
sampling method and collected extensive data on the interstitial fauna of the Sava River. We
collected nine samples per site – three 30-liter samples of each of the three types of hyporheic
habitat: shallow hyporheic zone (30 to 60 cm deep), deeper hyporheic zone and gravel bar
(both 60 to 90 cm deep). In Kresnice, where we tested the sampling method and the sample
volumes, we collected 10 and 20 liters per sample separately. Invertebrates from the 0.5 mm
mesh size fractions were sorted and identified to the lowest taxonomic level possible with
special attention given to stygobionts. We compared taxa numbers and specimen numbers
from different sample volumes, hyporheic types and locations. Results showed that for a
general overview of the interstitial fauna, extraction of 10l samples from shallow hyporheic
is sufficient, whereas detection of most stygobionts require extraction from deeper layers as
well. Overall, the shallow hyporheic was the most taxa rich, while the number of stygobiont
species was similar in all types of hyporheic. In terms of number of specimens, insects were
the most abundant in all types of hyporheic. The most species-rich locations were in the
upper and in the lower sampling section, while few taxa were found in the middle part due
to inaccessible terrain and probably also due to a series of hydroelectric power plants and
pollution. We also found species new to Slovenia and to science.
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