This study evaluated the standing crop biomass of freshwater snails and its spatial distribution according to four substrate types (boulders, cobbles, gravel covered with periphyton and gravel covered with macrophytes). The study site, in the Kupa River of the NW Dinarid area of Croatia, is in a karstic region. Depending on habitat, the gastropod wet biomass varied from 6.4 % to 43.8 % of the total macroinvertebrate biomass per unit area. The gastropods are the dominant component of biomass on boulder substrates in the upper region of the river, and on gravel substrates covered with macrophytes, in the lower course. It was found that gastropods are also the dominant component of the functional group of scrapers. The average annual gastropod biomass constitutes more than 80 % of scrapers at sampling sites in the upper and lower regions of the river.

The trophic role of rotifers in the zooplankton community of dimictic, oligotrophic lake Kozjak, the largest lake of the Plitvice Lakes, NW Dinarid Mountains, is analyzed. Their spatial and temporal biomass distribution in relation to that of protozoans, cladocerans and copepods shows that they form a significant part of the non-predatory zooplankton of this karstic standing water.

The community and trophic structure of benthic macroinvertebrates were studied in different types of habitats in the karstic Plitvice Lake system located in the NW Dinarid mountains (Croatia). The spatial distribution of functional macroconsumer groups shows that longitudinal community functional organization doesn't correspond with the River Continuum Concept (RCC) hypothesis. Collector guilds were the most abundant functional feeding groups at all the sites analyzed. The domination of shredders was found only in habitats in the source areas of the supply streams. The disturbed longitudinal community functional organization is caused by a discontinuum in the gradient of physical factors which is a result of the geomorphological origin of travertine barriers along the hydrosystem.

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