Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)

Héra, Zoltán: On experiences in monitoring molluscs (Mollusca) in the area of Duna-DrávanNational Park - A Duna-Dráva Nemzeti Park térségében végzett puhatestű (Mollusca) monitoring tapasztalatai

HÉRA Z.: ON EXPERIENCES IN THE MONITORING MOLLUSCS 33 The aim of sampling water snails by sweep netting is to study fauna living on the side of the river bed. Each sampling was taken on the gravel-free parts of the river bed. Comparing sample results to ones by quadrate sampling, frequency differences are quite striking due to different ground-base preferences. On Vízvár sampling site, when monitoring Amphimelania holandri (Pfeiffer, 1828) on species level, this species revealed an outstanding dominance (an average of 94%) on solid ground-base (the protective paving of the spurs), while this value, studied by sweep netting on a site rich in sediment only 2 m away, is only around 30%. The occurance frequency of Lithoglyphus naticoides reached 50% from former 4%. On the Bolhó sampling site the current is strong and has steep sideway bed. The occurance of Amphimelania holandri (Pfeiffer, 1828) is accidental, it has not occurred in the last few years due to the weaker tolerance of ground-base quality. One of the possible causes may have been the perturbation brought about by enforcement of gravel depositing bankside. The low species number of this sampling site is also characteristic. To get a clearer picture of the fauna, underwater individual sampling of water snails found on vegetation is carried out. Its purpose is to record species with a stable way of life whose presence is characteristically linked to vegetation and rarely found in float debris. In the course of samplings none of the species typically living on water plants were detected. Investigation of terrestrial snail fauna is also made up of several components. It is part of investigation carried out in alder woods of Lankóci woodland belonging to Gyékényes and data yielded by investigation of terrestrial fauna (12 species) are complemented by those of individual sampling (9 species). No changes in the frequency of dominant species Aegopinella ressmanni (Westerlund, 1833), Zonitoides nitidus (Müller, 1774), Perforatella incarnata (Müller, 1774) were found. Due to the nearness of Dombó Canal phytofag species requiring high humidity appear in this area on the borderline of assemblages. Rich slug fauna inhabits the biomass of tree trunks. Characteristic species are Avion circumscriptus (Joston, 1828), Arion subfuscus (Draparnaud, 1805), Deroceras agreste (Linnaeus, 1758), Limax cinereoniger (Wolf, 1803). An important component in the study of terrestrial snail species along the Dráva refers to water float debris. Table 4. contains average species frequency data collected during the five-year investigation. So far individuals of 38 species have been recorded, among them the occurance along the river of 2 protected species Vertigo angustior (Jeffreys, 1803) and Vertigo moulinsiana (Dupuy, 1849) have become known. In the float debris of Lake Bélavár we could determine 18 species. The vegetation and the ground surface are severely disturbed by dredging. The swept - in snail shells come from the surrounding weeds and soft-wood groves. Some of them are supposed to be subfossil. Literature HÉRA, Z., VARGA, A. 2001: Somogy megye puhatestű (Mollusca) faunája - Natura Somogyiensis 1: 29-40. HÉRA, Z. 2002: Újabb adatok Somogy megye puhatestű (Mollusca) faunájának ismeretéhez - Natura Somogyiensis 3: 23-26. Soós, L. 1933: Malakofaunisztikai adatok a Dunántúlról - Állattani Közlemények 30: 12-26. VARGA, A., BÁNKÚTI, K., KOVÁCS, T. 1995: Az Arion lusitanicus Mabille, 1868 magyarországi terjedése Malakológiai Tájékoztató 14: 17-20. VARGA, A., UHERKOVICH, Á. 1998: A Dráva menti puhatestű (Mollusca) fauna kutatásának újabb eredményei - Dunántúli Dolgozatok Természetudományi Sorozat 9: 43-68.