Opusc. Zool. Budapest, 2015, 46(2): 183–197 Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains (Danube-Drava National Park, Hungary): rare and alien species A. KISS, E. ÁGOSTON-SZABÓ, M. DINKA & Á. BERCZIK Anita Kiss, Edit Ágoston-Szabó, Mária Dinka & Árpád Berczik, Centre for Ecological Research of HAS Danube Research Institute, H-1113, Budapest, Karolina út 29. Hungary, [email protected], agoston- [email protected], [email protected], [email protected] Abstract. The composition of microcrustacean fauna was investigated in different water bodies of Gemenc-Béda-Karapancsa Floodplains with special regard to the distribution of alien and rare taxa. Between 2002 and 2013 101 taxa (57 Cladocera, 27 Copepoda, 17 Ostracoda,) were recorded from the water bodies with differing degrees of connectivity to the main river (eu-, para-, plesio- and paleopotamon). 18 species are reported for the first time from the area of Danube-Drava National Park and among them Daphnia ambigua, Pleuroxus denticulatus and Eurytemora velox are allochtonous species in Hungary. E. velox and P. denticulatus have persistent populations in the area, but their contribution to floodplain biodiversity is still not significant. Daphnia ambigua has only local and temporal populations and its presence is confined to the disconnected side of the floodplain. The abundance of thirty species was very low and their distribution pattern in the floodplain is different. The microcrustacean diversity of the plesiopotamal side arms is remarkable, particularly in the Nyéki-Holt-Danube. Keywords. Alien species, Cladocera, Copepoda, Ostracoda, species richness, Gemenc-Béda-Karapancsa Floodplains. INTRODUCTION form an UNESCO Biosphere Reserve. This area is the largest active floodplain in Europe with F loodplains are an important area of biodi- unique natural value (Zinke 1996). It lies comple- versity, providing habitat for endangered or tely within the dike system, namely the character- threatened species. Floodplain rivers are distur- istic hydrological processes of the river floodplain bance-dominated ecosystems characterized by system are not disturbed. high levels of habitat diversity and biota adapted to exploit the spatio-temporal heterogeneity (Junk Limited number of studies is dealing with the et al. 1989, Amoros & Roux 1988, Ward & Cladocera, Copepoda and Ostracoda fauna of this Stanford 1995). Ecotones, hydrological connecti- area. The first data was presented by Bothár vity, and succession processes play major role in (1980) describing 18 Cladocera and 10 Copepoda structuring the spatio-temporal heterogeneity species in the Vén-Danube and in the main arm leading to the high biodiversity that characterizes near Baja. In 1994 Körmendi (2007) recorded 10 floodplain rivers. Cladocera and 10 Copepoda taxa from different dead arms and temporary pools of Gemenc flood- The Gemenc-Béda-Karapancsa Floodplains of plain. The most comprehensive description of the the Danube River (rkm 1497–1440) part of the fauna was published by Forró & Meisch (1998). Danube-Drava National Park (Hungary) repre- Their studies revealed 118 crustacean species sents an exceptional example of river-floodplain (Anostraca, Notostraca, Cladocera, Copepoda, systems in Europe with meanders, oxbow lakes, Ostracoda, Isopoda, Amphipoda and Mysida) marshlands, and extended hardwood forests. from the Drava region of the Danube-Drava These floodplains are also Natura 2000 areas and National Park based on collectings between 1995 _______________________________________________________________________________________________________ urn:lsid:zoobank.org:pub:7D172826-9C0F-41C0-9B58-8CC14DF83FF5 HU ISSN 2063-1588 (online), HU ISSN 0237-5419 (print) http://dx.doi.org/10.18348/opzool.2015.2.183 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species and 1997. In 1999 Körmendi and Lanszki (2002) For our investigation the following sites were recorded 37 Cladocera and 11 Copepoda taxa chosen: 1. Eupotamon: the main channel, with from various water bodies of Danube-Drava Nati- permanent flow; bottom composed of stones, onal Park. Between 1997 and 1998 Csányi et al. gravel and coarse sand; macrophytes are absent. (1998) examined the zooplankton assemblages in 2. Parapotamon: side arms permanently connect- the Vén-Danube, Nyéki-Holt-Danube and the ed to the main channel; bottom composed of main arm near to Baja reporting on 15 zooplank- gravel mixed with sand and silt; macrophytes are ton taxa. scarce. 3. Plesiopotamon: permanent or temporary standing water bodies with no permanent and Between 2002 and 2013 detailed investigations direct connection to the main arm, connection were carried out and part of this project was to with the main arm at higher water levels; examine the zooplankton assemblages in water upstream end is often silted up; the bottom bodies with differing degrees of connectivity to consists of silt and clay, macrophytes could grow the main river on a near natural temperate river- densely and highly influenced by the discharge of floodplain system (e.g. Schöll & Kiss 2008, Kiss the river. 4. Paleopotamon: former anatomised & Schöll 2009, Kiss et al. 2014). channels or meanders with no direct connection to the river, slightly influenced by the river dis- Here we summarize the faunistic results of this charge, the bottom consists of silt and clay, long-term study focusing the presence and distri- macrophytes grow very densely (Guti 2001). bution of rare and alien microcrustacean species and furthermore, the species composition of A total of 66 sampling sites were selected and different water bodies on the floodplain. divided into four functional groups: eupotamon (3 sites), parapotamon (Vén-Danube, Rezéti-Holt- MATERIALS AND METHODS Danube, 12 sites), plesiopotamon (Grébeci-Holt- Danube, Nyéki-Holt-Danube, Cserta-Danube, Study area Sárkány-fok, Címer-fok, Külső-Béda, Mocskos- Danube, 35 sites), 4. paleopotamon (Riha Oxbow Covering some 25,000 ha, the Gemenc-Béda- 16 sites) (Fig. 1.). Besides the regularly used Karapancsa Floodplains of the Danube River is sampling sites, additional sites were also selected situated between rkm 1497 and 1440. In this reach between 2007 and 2009, during the floods the mean annual discharge is 2400 m3 s–1, with a (VDU5; RDU6, 7, 8, 9; GDU6) and among minimum of 618 m3 s–1 and a maximum of 7940 different macrohyte stands in the Mocskos-Da- m3 s–1. The water level is monitored by an official nube and Riha Oxbow (19 sites). Sampling was gauge at Baja (rkm 1479; 46 °10,41’ N, 18° carried out between April 2002 and October 2013, 55,29’ E), which recorded a maximum amplitude the sampling years were between 2002 and 2004, of 9 m. In the main arm the slope is about 5 cm 2007 and 2009 and 2012 and 2013. km–1, with a velocity of 0.8–1.2 m s–1 at mean water level. The river starts to overflow into the The sampling sites and sampling dates were floodplain above a water level of 500 cm at Baja. the following: Different riverine functional units can be ob- Eupotamon served in the study area, thus providing opportu- nity for simultaneous comparisons. The typology Main arm of the Danube of the water bodies was based on the functional D1489: 1489 rkm, Érsekcsanád, N46° 16,403' E18° 54,547', classification of Amoros et al. (1987), which de- in front of the mouth of Grébeci-Holt-Danube. pends on the flow velocity of the branches and on 2002 (08. 04., 03. 07.), 2003 (07. 05., 08. 07., 15. 09. 27. the intensity of lateral connectivity between the 10.), 2004 (04. 14., 27. 05., 01. 07., 26. 08., 27. 10.), 2007 main channel, the side arms, and the backwaters. (23. 05., 11. 09., 25. 09.), 2008 (29. 07), 2009 (07. 04., 28. 184 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species 04., 03. 06., 09. 06., 11. 06., 29. 06., 21. 06., 03. 08., 01. 09., Nyéki-Holt-Danube (NYHD) 06. 10., 27. 10.) This strictly protected oxbow is situated in the D1482: Baja (N46º11,412’ E18º55,610’) right side of the Danube (rkm 1479) in the active 2008 (29. 07.), 2009 (29. 06., 21. 07., 03. 08.) floodplain. It is a natural cut-off river meander which evolved during the end of the 18th century. D1437: 1437 rkm, Mohács, N45º55,967’ E18º 46,433’, The oxbow together with the Cserta-Danube, beyond the harbour of the ferry. Sárkány- and Címer-fok form a complex hydro- 2007 (25. 07., 29. 08., 25. 10.), 2008 (18. 03., 10. 06.), 2009 (22. 06., 28. 07.), 2012 (16. 05., 19. 06., 04. 07., 07. 08., 04. logical unit. The threshold level of the surface 09., 09. 10.), 2013 (26. 06., 12. 10.) hydrological connection of NYHD up- and down- stream is reached when the water level of the Parapotamon Danube River at rkm 1478.7 (Baja gauge station) is 520 cm and 570 cm, respectively. Upstream it Vén-Danube (VDU) is achieved through Vén–Duna (VDU), Cserta– 5 km long side arm with constant flow. It was Duna (CSDU) and Sárkány–fok (SÁF), while the part of the main arm until the interception in downstream – through the Címer-fok (CIF). Its 1897-1898. channel is silting up and it has a high macrophyte VDU2 (N46º11.880’ E18º55.177’), VDU3 (N46º12.118’ cover (Ágoston-Szabó et al. 2014). E18º53.843’), VDU4 (N46º12.754’ E18º53.940’), small NYHD1 (46º 11,642’ 18º 50,991’), NYHD2 (46º 11,563’ 18º periodical inflow: VDU5 (N46º12.346’ E18º53.732’) 50,834’), NYHD3 (46º 11,489’ 18º 50,937’), NYHD4 (46º 2002 (08. 04., 02. 05., 13. 06., 03. 07., 12. 11.), 2003 (07. 11,573’ 18º 51,175’), NYHD5 (46º 11,433’ 18º 50,756’) 05., 08. 07., 15. 09. 27. 10.), 2004 (04. 14., 27. 05., 01. 07., 2003 (07. 05., 08. 07., 15. 09.), 2004 (27. 05., 01. 07.), 2009 26. 08., 27. 10.), 2007 (23. 05., 11. 09., 25. 09.), 2008 (29. (07. 04., 28. 04., 03. 06., 09. 06., 11. 06., 29. 06., 21. 06., 03. 07.), 2009 (29. 06., 21. 07., 03. 08.) 08., 01. 09., 06. 10., 27. 10.) Rezéti-Holt-Danube (RDU) Cserta-Danube (CSDU) 15 km long side arm, it was the main arm until CSDU (N46°11,783' E18°53,053') is a plesi- the interception in 1893-1894. opotamal side arm of the Vén-Danube (VDU). It RDU2 (N46º14.224’ E18º53.192’), RDU3.1 (N46º14.767’ together with Sárkány- and Címer-fok is part of E18º52.541’), RDU4 (N46º16.015’ E18º53.645’), RDU5 the so-called fok-system, which are typical sec- (N46º15.599’ E18º53.623’), small periodical inflow: RDU6 tion of the local hydrological system. The creation (N46º16.208’ E18º52.671’), RDU7 (N46º16.237’ of the fok-system (drainage canals) was the most E18º52.373’), RDU9 (N46º13,412’ E18º51,967’), stagnant important human impacts, which changed the temporary water body: RDU8 (N46º13.950’ E18º51.918’) hydrological condition of the floodplain (Guti 2002 (08. 04., 02. 05., 13. 06., 03. 07., 12. 11.), 2003 (07. 2001). 05., 08. 07., 15. 09. 27. 10.), 2004 (04. 14., 27. 05., 01. 07., 26. 08., 27. 10.), 2007 (23. 05., 11. 09., 25. 09.), 2008 (29. CSDU1 (N46º11,541’ E18º52,431’) CSDU2( N46º11,761’ 07.), 2009 (29. 06., 21. 07., 03. 08.) E18º53,121’), CSDU3 (N46º12,133’ E18º53,756’) 2003 (07. 05., 27. 10.), 2007 (25. 09.) Plesiopotamon Sárkány-fok (SÁF) Grébeci-Holt-Danube (GDU) SÁF (N46°11,816' E18°51,594') is a narrow 7 km long side arm, it was the part of the main channel between the NYHD and the CSDU. arm until the interception in 1895-1896. 2 sampling sites GDU1 (N46º16.495’ E18º54.104’), GDU2 (N46º17.202’ 2003 (07. 05., 08. 07., 15. 09.) E18º52.921’), GDU3 (N46º17.451’ E18º55.610’), GDU4 (N46º17.638’ E18º53.162’), GDU5 (N46º17.641’ Címer-fok (CIF) E18º53.261’), small temporary inflow: GDU6 (N46º17.682’ CIF (N46°46,781' E18°50,723') is a narrow E18º53.210’) channel between the NYHD and the main arm of 2002 (08. 04., 02. 05., 13. 06., 03. 07., 12. 11.), 2003 (07. the Danube. 2 sampling sites 05., 08. 07., 15. 09. 27. 10.), 2004 (04. 14., 27. 05., 01. 07., 26. 08., 27. 10.), 2007 (23. 05., 11. 09., 25. 09.), 2003 (07. 05.) 185 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species Mocskos-Danube (MDU) 2012 (16. 05., 19. 06., 04. 07., 07. 08., 04. 09., 09. 10.), 2013 This side arm (rkm 1442-1440) is situated in (26. 06., 23. 07., 18. 09.) the active floodplain of Béda-Karapancsa area. Collecting and identification Approximately 3.4 km long, 60 meter wide, with shallow water (average depth: 1.5 m) and very Microcrustaceans were collected with plankton dense macrovegetation. It has a temporary con- net (mesh size 70 µm, N= 1) by filtering 10 X 10 nection with the Danube, the water flowing at 700 L of water from the main arm and 5 X 10 L of cm (gauge of Mohács rkm 1447) at the upper end water from the side arms, then preserved in 4% and at 550 cm at the lower end of the oxbow. The formalin. The three examined groups of crusta- water of MDU only rarely flows (1–5 times per ceans were enumerated by using inverted micros- year), and this take place only for short periods at copy and identified to species level. Microcrus- a time (gauge of Mohács 550 cm). tacean abundance, including copepodids, was MDU1 (N45º57’24,8” E18º46’24,7”), MDU2 (N45º57’35,3” evaluated by enumerating individuals in the whole E18º46’38,2”), MDU4 (N45º57’58,7” E18º46’43,9”), MDU5 sample. Gulyás & Forró (1999, 2001), Meisch (N45º58’06,2” E18º46’37,1”), MDU7 (N45º58’18,3” E18º 45’57,1”) and further seven sampling points among the (2000) and the nomenclature of Dussart (1967, submerged macrovegetation near to the regularly used sites. 1969) were used for species identification. 2009 (22. 06., 28. 07.), 2012 (16. 05., 19. 06., 04. 07., 07. 08., 04. 09., 09. 10.), 2013 (26. 06., 23. 07., 18. 09.) RESULTS AND DISCUSSION Külső-Béda (BDU) Faunistic results It is situated on the right bank of the Danube (N45º55,767’ E18º45,420’) in the active flood- Between 2002 and 2013 101 taxa (57 Cla- plain of Béda-Karapancsa. Its open water area is 4 docera, 27 Copepoda, 17 Ostracoda,) were record- km long, 90 m wide on average and is about 2.5 ed (Appendix 1) and 18 species reported which m deep. Its upstream junction with main channel have not been mentioned earlier from the area of of the Danube is at the rkm 1440.5, while the Duna-Drava National Park. These are the follow- downstream junction, the mouth is at rkm 1437.5 ings: Cladocera: Alona intermedia Sars, 1862; of the Danube. The upstream surface connection Bosmina longispina Leydig, 1860; Ceriodaphnia of BDU occurs only during high floods, above dubia Richard, 1894; Chydorus gibbus Sars, 630 cm water level of the Danube (at gauge of 1890; Daphnia ambigua Scourfield, 1946; Mohács rkm 1447) (Ágoston-Szabó et al. 2013). 5 Dunhevedia crassa King, 1853; Holopedium sampling sites gibberum Zaddach, 1855; Pleuroxus denticulatus 2007 (25. 07., 29. 08., 25. 10.), 2008 (18. 03., 10. 06.) Birge, 1879; Copepoda: Canthocamptus staphy- linus (Jurine, 1820); Cyclops insignis Claus, 1857; Paleopotamon Cyclops scutifer Sars, 1863; Eurytemora velox (Lilljeborg, 1853); Paracyclops affinis (Sars, Riha Oxbow (RIH) 1863); Ostracoda: Bradleycypris obliqua (Brady, This oxbow is located on the protected side of 1868), Bradleystrandesia reticulata (Zaddach, the floodplain and it has no connection with the 1844); Cypris pubera O. F. M., 1776; Noto- main channel. It is 4.5 km long and 80 m wide. dromas monacha (O. F. Müller, 1776); Para- The average water depth is approximately 1-1.5 candona euplectella (Robertson, 1889). m. It is a strictly protected nature reserve areas covered by dense macrovegetation. Most of the collected microcrustacean species RIH1 (N46°00'08,1" E18°44'33,9"), RIH21 (N46°00'44,6" are widespread and characteristic of the fauna of E18°45'10,3"), RIH22 (N46°00'35,4" E18°46'14,2"), RIH3 the littoral zone in floodplain water bodies and (N46°00'09,6" E18°46'30,9") and further 12 sampling points lakes. The number of the detected taxa was sig- among the submerged macrovegetation near to the regularly used sites. nificantly higher than the published results of pre 186 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species Figure 1. Sampling sites on the Gemenc-Béda-Karapancsa Floodplains (Gemenc floodplain: Grébeci-Holt-Danube (GDU), Re- zéti-Holt-Danube (RDU), Vén-Danube (VDU), Cserta-Danube (CSDU), Sárkány-fok (SÁF), Nyéki-Holt-Danube (NYHD), Címer-fok (CIF), Béda-Karapancsa floodplain: Riha oxbow (RIH), Mocskos-Danube (MDU), Külső-Béda (BDU) vious studies (Bothár 1980: 28 taxa; Csányi et al. Pleuroxus denticulatus and Eurytemora velox are 1998: 15; Körmendi & Lanszki 2002: 47; Kör- alien or non-native (allochtonous) species in Hun- mendi 2007: 16) with the exception of the invest- gary. The abundance of thirty species was irrele- tigation of Forró & Meisch (1998) (111 taxa), but vant; in these species less than 10 individuals in our studies the area of sampling was more were collected between 2002 and 2013. These extensive and the duration of the survey was were regarded as rare species in Gemenc-Béda- longer than any other studies. All of the species Karapancsa Floodplains. reported by Csányi et al. (1998) and Körmendi (2007) were also recorded in our studies. 27 Alien species species in the study of Bothár (1980), 43 in Körmendi and Lanszki (2002), as well as 73 taxa The copepod genus Eurytemora occupies a in the investigation of Forró and Meisch (1998) wide range of habitat types throughout the also occurred between 2002 and 2013. Northern Hemisphere, with among the broadest salinity ranges of any known copepod. Eury- There were significant differences in the spe- temora velox, as originally salt water species is cies richness between water bodies with differing widely distributed in the brackish waters from the degrees of connectivity with the Danube Arctic Ocean and the Baltic Sea shore to South- (Appendix 1). Species richness was the highest in eastern Europe, the Sea of Azov, and the Caspian the plesiopotamon, which has no permanent and Sea. This euryhaline species migrated from the direct connection to the main arm. Among the estuaries of the North Sea upstream of many newly detected species, Daphnia ambigua, rivers (Tollinger 1911) and from the Black Sea 187 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species upstream in the Danube River (Gaviria & Forró of Szigetköz (Northwestern Hungary, 1850–1793 2000). In the Middle Danube Basin this species rkm) the abundance of this species was also not was collected for the first time in Hungary in significant at the monitoring sites of Szigetköz 1991 (Forró & Gulyás 1992), also in Slovakia Monitoring Network between 1999 and 2013. (Vranovský 1994) and Austria (Gaviria & Forró, During the fourteen years of monitoring only 155 2000) in the very same year. In the last twenty specimens were collected from the three section years E. velox was presumably spread in the of Szigetköz (main arm connected and recon- whole Hungarian section of the Danube and in nected floodplain). many freshwater habitats of Hungary also. For example, in the Lake Fertő (the westernmost and Pleuroxus denticulatus is also an allochtonous largest steppe lake in Eurasia, situated on the species in the Middle Danube Basin. It was de- Hungarian-Austrian border) this species showed scribed from North America (Birge 1879) and its up for the first time in 2009 then spread gradually range is restricted to the northern hemisphere and in 2012 a total of 492 specimens were (Frey 1993). This North-American Cladocera collected (Kiss et al. 2014). occurs in Europe since the 1970s. This species is a new invader from Western to Central Europe and In the area of the Danube-Drava National Park its occurrence in the Danube probably corres- ponds with the opening of the Rhine-Main- the presence of E. velox was recorded in 2002 Danube Canal (Hudec & Illyová 1998). The first (Kiss & Schöll 2009), the previous faunistic occurrence of P. denticulatus in the Hungarian works (Körmendi 2007, Körmendi & Lanszki section of the main channel was reported in 1992 2002, Forró & Meisch 1998) did not mention this at rkm1669 (Bothár 1994), since then it has been species. In our investigation altogether 622 indi- spread in the main arm (Gulyás 1995, Kiss & viduals of E. velox were collected between 2002 Schöll 2009, Vadadi et al. 2009). Similar to E. and 2013. Most of the individuals were in the velox, P. denticulatus was also not revealed by the plesiopotamal Mocskos-Danube (297 individuals) previous studies from the Danube-Drava National and the distribution of this calanoid differed Park (Körmendi 2007, Körmendi & Lanszki 2002, significantly between the examined water bodies Forró & Meisch 1998, Csányi et al. 1998). In the (Fig. 2. A). Larger part of the collected specimens study area, P. denticulatus was firstly collected in occurred in the plesiopotamal wetlands which are 2003 from the Cserta-Danube and Sárkány-fok, situated close to the main arm and often connect- then it was spread the whole active floodplain, but ed with the Danube. Similarly to our observation in the protected side of the floodplain this species in Lake Fertő (Kiss et al. 2014), the number of the does not occur yet (Fig. 2. C). collected individuals differed year by year and there was a significant increase from 2009 (Fig. 2. According to our result, this species was B). spread in the whole river-floodplain system and it supposedly has permanent population in the In the sampled habitats this calanoid often floodplain, but its density was very low, only coexisted with other calanoids, Eudiaptomus forty specimens were collected between 2003 and vulgaris and/or Eudiaptomus gracilis. The num- 2012. Similar trend can be observed in the area of ber of E. velox was significantly higher than the Szigetköz, where only 67 individuals were col- two Eudiaptomus species (Fig. 3.) similarly to the lected between 1999 and 2013 (A. Kiss unpub- observation of Vad et al. (2012). Opposite to lished result). This alien cladoceran was mostly other observations, e.g. soda pan in western Hun- found in the littoral zone, between submerged or gary (Horváth & Boros 2010) or two artificial emergent macrophytes. It was usually found to- lakes in the region of the North Hungarian gether with typical littoral cladocerans, especially Mountains (Vad et al. 2012), E. velox is still not a Pleuroxus aduncus, P. truncatus, similar to the dominant member of Copepoda assemblages in observations of Hudec and Illyová (1998) and Gemenc-Béda-Karapancsa Floodplain. In the area Vad et al. (2012). 188 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species Figure 2. The distribution of the three alien species in the study area between 2002 and 2013 (A and B = Eurytemora velox, C and D = Daphnia ambigua and Pleuroxus denticulatus). Figure 3. Distribution of the three Calanoida species in the study area between 2002 and 2013. Daphnia ambigua, one of the most broadly well. In our studies D. ambigua was found only at distributed members of its genus, occurs in Eu- two sampling sites of the paleopotamal Riha Ox- rope as well as in North and South America (Her- bow, in May 2012. Only 25 individuals were bert et al. 2003). This species is native to the collected together with Daphnia cucullata, D. lon- temperate regions of North America and it was gispina, Bosmina longirostris, Ceriodaphnia pul- introduced to Europe where it is now broadly chella, Chydorus sphaericus, Eurytemora velox, distributed (Maier 1996). Similarly to Pleuroxus and seven other species. In the area of Szigetköz denticulatus, it has been spreading from Western (northwest Hungary) between 1999 and 2013, to Central Europe in the last few decades only one individual of D. ambigua was found in (Vranovský & Terek 1996). In Hungary D. am- 2006, in the Schisler-dead arm (A. Kiss unpub- bigua is a rare species, their presence was con- lished result). firmed especially from the Danube (Gulyás & Forró 1999, Kiss & Schöll 2009), but Vad et al. It is obvious that Eurytemora velox and (2012) found this species in an artificial lake in Pleuroxus denticulatus have a permanent popu- the region of the North Hungarian Mountains as lation in Gemenc-Béda-Karapancsa Floodplains, 189 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species but according to our results D. ambigua is still not reticulata, Notodromas monacha and Paracan- permanent member of the fauna and its local and dona euplectella are new species for the Danube- occasional presence could be correlated with bird- Drava National Park. mediated dispersal (Riha Oxbow is an important area used by migratory birds). Holopedium gibberum is one of the most in- frequent microcrustacean species in Hungary Species of zooplankton, especially cladocerans being reported only from the Danube (Gulyás & can easily spread with passive transport (via wind, Forró 1998). In our study, three individuals of water or birds), mainly due to their ability to Holopedium were collected in September 2007 create resting eggs (Havel et al. 1995). The role of from the Rezéti-Holt-Danube (Kiss & Schöll human-mediated vectors is also noteworthy espe- 2009). In the beginning of September 2007 there cially for species dispersal across geographical was an extreme water level (797 cm, Baja gauge) in the flooding period and our sampling was in the barriers and into large aquatic ecosystems. Dia- receding period when the mixing floodplain wa- pausing stages facilitate species survival during ters start to flow back toward the main arm. This movement across geographical barriers under holarctic species prefers mainly cool, oligo- extreme conditions, such as in ballast tanks of trophic, soft-water lakes with low pH (Balcer et ships (MacIsaac et al. 2001). al. 1984) and it is noteworthy that the resting eggs of Holopedium are poorly adapted for transfers Rare species among habitats (Cox & Hebert 2001). Supposedly we found a small temporary population of Holo- The abundance of thirty species (13 Cladocera, pedium, which was transported by the flood. 10 Copepoda, 7 Ostracoda) is insignificant, less than ten individuals were collected between 2002 Similarly to Holopedium, the two individuals and 2013. In case of nine species only one indi- of Cyclops insignis were detected in September vidual was found in the whole period of sampling. 2007 as well in the receding period of the flood. Twenty-two species were mentioned by earlier Both species prefer mainly small standing water works (Bothár 1980, Forró & Meisch 1998, habitats and lower water temperature. The carni- Körmendi & Lanszki 2002, Körmendi 2007), vorous cladoceran, Polyphemus pediculus was accordingly these species are supposedly perma- also reported from many localities of Hungary nent members of the local fauna. (Gulyás & Forró 1999), but only eight specimens was collected from Nyéki-Holt-Danube. Among Most of the rare species were distributed in the the former works, it was only reported by Forró connected floodplain, in the plesiopotamon and and Meisch (1998) from two localities of Drava especially in the Nyéki-Holt-Danube (Fig. 4. A- region. C). Among the sampling years, the number of rare species was the highest in 2003 and 2009. This Out of the seven rare ostracods three (Bradley- result could be subsequent upon our sampling strandesia reticulata, Candona weltneri, Para- program and the hydrological events. In 2003 all candona euplectella) were collected in the Nyéki- of the potamon-types were investigated at the Holt-Danube in 2003, when the water level of the same time and extensive macrovegetation deve- oxbow was extremely low. These species prefer loped in many places in the floodplain because the small water bodies with swampy or boggy bot- water level was low in the main arm. In 2009, a tom. The neustonic ostracod, Notodromas mona- detailed study was launched in the Nyéki-Holt- cha is widely distributed across the Holarctic Danube, which is the most diverse area in region and common everywhere in suitable Gemenc-Béda-Karapancsa-Floodplains. habitats (Meisch 2000). In Hungary it is recorded from many localities and sometimes was Among the rare species, Holopedium gibbe- multitudinous in the plankton (e.g. Kiss 2007). rum, Ceriodaphnia dubia, Cyclops insignis, Cyp- Curiously, the only collected specimen of ris pubera, Paracyclops affinis, Bradleystrandesia Notodromas occurred in the main arm. 190 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species Figure 4. Species richness of the rare species in the study area. A = the number of taxa in the connected (eu-, para- and plesio- potamon) and in the disconnected (paleopotamon) floodplain, B = the number of taxa in the sampling sites, C = the number of taxa the different functional units, D = The occurrence of rare species in the different sampling years. In our studies, the scarce occurrence of some receding period of the flood. These water bodies taxa, e.g. benthic Paracyclops spp., Ectocyclops are small channels, branching out from side arms, phaleratus, Harpacticoida or bottom-dwelling ost- hydrologically interconnecting them to the flood- racods (Candonidae, Limnocythere) is evident be- plain (Schöll et al. 2012). Compare to the main cause we did not collect from the benthos. arm, there was no difference in the average number of taxa, 9 but the maximum number of Microcrustacean species richness in water taxa per sample (10) was higher than the bodies with differing degrees of con- eupotamon. The most significant species were the nectivity with the main arm characteristic species of the main arm and Thermocyclops spp., but the tychoplanktonic and phytophilous taxa were also occurred. The species richness, the average, and maxi- mum number of taxa were different in the studied The species richness (83 taxa: 45 Cladocera, water bodies and were the highest in the plesio- 26 Copepoda, 12 Ostracoda) and the number of potamon (Fig. 5). rare taxa (20), the average (7.23) as well as the maximum (22) number of taxa were the highest in 36 taxa (N = 54) were collected from the eu- the plesiopotamon. 28 taxa reported from the potamon, the most frequent species were Bos- plesiopotamon alone and the number of tycho- mina longirostris, Chydorus sphaericus and Acan- planktonic and phytophilous taxa was significant. thocyclops robostus which are typical for the There were significant differences in the species Hungarian section of Danube. The average num- richness between the studied plesiopotamal side ber of taxa was 3.85 and the differences between arms. In the Gemenc-Béda-Karapancsa Flood- the three sampling sites of the main arm were plains, Nyéki-Holt-Danube was proved to signi- irrelevant. ficantly important area of microcrustacean diver- sity. Despite of the relatively small number of In the parapotamon the species richness (57 samples (N = 50), the species richness (60 taxa) taxa, N = 143) and the number of rare taxa (10) and the number of rare taxa (11) were the highest increased and 9 taxa occurred in this functional in the area. The species richness was also notably unit alone. Among these species, Holopedium in the fok-system (41 taxa, N =13), but contrary to gibberum and Diaphanosoma mongolianum were this, only 22 taxa were detected in the Külső-Béda found in the conjuctive water bodies in the (22). 191 Kiss et al.: Microcrustacean diversity in the Gemenc-Béda-Karapancsa Floodplains: rare and alien species Figure 5. The species richness of microcrustaceans in the different potamon-types (A) and in the different sampling sites (B) ( see text for further explanation.) In the paleopotamon (N = 72) 43 taxa were velox and P. denticulatus have persistent popu- collected and average (6.23) and maximum lations in the area, but their contribution to flood- plain biodiversity is still not significant. Daphnia number of species (15) as well as the number of ambigua has only local and temporal populations rare taxa (4) decreased compare to the significant and its presence is confined to the disconnected part of the plesiopotamal side arms. The high side of the floodplain. proportion of tychoplanktonic and phytophilous taxa in the assemblages is obvious. Many works Acknowledgements — The study was supported by the (e.g. Tockner et al. 1998) published positive NKFP-3B/0014/2002 and the Deutsche Bundesstiftung Umwelt (DBU, AZ 24050) projects. correlation between the species richness and the degree of connectivity between the main channel REFERENCES and the backwaters, but according to our obser- vation the species diversity of microcrustaceans ÁGOSTON-SZABÓ E., SCHÖLL K. & DINKA M. (2013): was the highest in the plesiopotamon and not in Limnological characteristics of a Danube oxbow- the disconnected floodplain. lake (Danube-Drava National Park, Hungary). River Systems, 20(3-4): 277–287. CONCLUSION doi: 10.1127/1868-5749/2013/0055 ÁGOSTON-SZABÓ E., SCHÖLL K., KISS A., BERCZIK Á. Between 2002 and 2013 101 taxa were re- & DINKA M. (2014): Decomposition of willow leaf corded in the area of Gemenc-Béda-Karapancsa litter in an Oxbow Lake of the Danube River at Floodplains and 18 species proved to be new for Gemenc, Hungary. Acta Zoologica Bulgarica the region. The species richness and composition Suppl., 7: 197–202. of the fauna were different in the examined floodplain water bodies and the number of AMOROS C. & ROUX A.L. (1988): Interaction between water bodies within the floodplains of large rivers: microcrustacean species was most significant in function and development of connectivity. Müns- the plesiopotamon. The fauna of the plesio- tersche Geographische Arbeiten, 29: 125–130. potamal Nyéki-Holt-Duna is noticeably diverse and this oxbow is a “diversity hotspot” in the AMOROS C., ROUX A. L., REYGROBELLET J. L., floodplain. This study proved the presence of BRAVARD J. P. & PAUTOU G. (1987): A method for Dahnia ambigua, Pleuroxus denticulatus and applied ecological studies of fluvial hydrosystems. Eurytemora velox and confirmed the expansion of Regulated Rivers: Research & Management, 1: 17– these non-native species in the floodplain. E. 36. doi: 10.1002/rrr.3450010104 192