Macrozoobenthos as an Indicator of the Level of the Trophy and Saprobit,y of Lake JarrunSun, / I I ( L T~: During complex ecological investigations on La,lie Jiwiin (and neighbouring interst,itial underground \vat,ers) which took place in 1984 and 1985, niacrozoobenthos was also studied. I t s qualitative and quantitativr composition in a lmge part deprnds 011 the degree of t,rophy and saprobity of the water. Specially examined mere the oligochnetes and chironomids larvae, which besides having R large numerical perceiit.agr also occurred with R large number of species. I n addition, t,he representatives of other groups of macroscopic invertebrat'es mere also mentioned, especially those which have a special significance as indicators of a certain degree of trophy and saprobity, and which are important because of their oasis preservation in this ecosystem.

After the formation of a drinking water reservoir at Butoniga, Istria, research on the fauna of the Chironomidae larvae was undertaken in the feeder waters and the reservoir itself. Forty eight species were identified, belonging to the subfamilies Chironominae, Orthocladiinae, Diamesinae and Tanypodinae. Chironomidae colonized the reservoir waters relatively more quickly than other groups of macroscopic invertebrates. The similarity quotient (QS) of Chironomidae of the feeder waters and the reservoir is only 37.8%, which points to the formation of new communities in the reservoir. There were qualitative and quantitative changes in the composition of Chironomidae fauna in the river Mirna and in the river Butoniga downstream from the dam after water was released from the reservoir for the purpose of testing the dam. The Chironomid composition of the feeder waters places them in quality grade II. In the Butoniga reservoir the bottom water was assigned to grade II-III, because of the decomposition of the remains of surface fauna.

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