Biologia, Bratislava, 62/3: 345—350, 2007 Section Zoology DOI: 10.2478/s11756-007-0057-9

Spatial pattern of water bugs (Nepomorpha, Gerromorpha) at different scales in the Szigetk¨oz (Hungary)

János N. Nosek1, Tamás Vásárhelyi 2, Gábor Bakonyi3 & Nándor Oertel1

1Hungarian Danube Research Station of HAS, Jávorka S. u. 14,H-2131 G¨od, Hungary; e-mail: [email protected] 2Hungarian Natural History Museum, Baross u. 13,H-1088 Budapest, Hungary 3SzIU Department of Zoology and Ecology, Páter K. u. 1,H-2100 G¨od¨oll˝o, Hungary

Abstract: In 2003, 26 Heteroptera species (16 aquatic and 10 semiaquatic) were collected from 53 sampling sites in the Szigetk¨oz region in Hungary. Ilyocoris cimicoides and Gerris argentatus were the most frequent aquatic and semiaquatic species, respectively. Large differences both in the species number and species composition were observed among the different flood-prevention areas, arm systems and habitats. Strong negative correlation was found between the average number of aquatic species and current velocity, and a strong positive correlation between the average number of aquatic and semiaquatic species and macrophyte density. From a faunistic point of view, the marsh at Arak is the most interesting and valuable site. Key words: Heteroptera; Nepomorpha; Gerromorpha; biodiversity; Danube River; Szigetk¨oz

Introduction Sampling sites can be identified by the name of the water body or the nearest site, with the aid of the river kilometre There are very few data on the aquatic and semi- mark (rkm) and the code of the site. Sites were selected in aquatic bug (Heteroptera: Nepomorpha and Gerromor- order to ensure habitat diversity was as high as possible. pha) fauna of the Szigetk¨oz arm system of the Danube The sites are as follows: ¨ River. Only sporadic faunistical data are available con- 1. Danube main arm, (Oreg-Duna, Old Danube, DUF), abandoned main arm, 13 sampling sites): Dunaki- cerning the occurrence of some species (Bakonyi 1990; ◦   ◦   liti 1845 rkm (DKI4 /47 59 41.0 N, 17 18 51.0 E/, DKI5 Ambrus et al. 1995; Nosek 1996). Systematic sampling /47◦5940.3 N, 17◦1849.1 E/, DKI6 /47◦5940.0 N, programmes have been carried out only twice, at the 17◦1846.7 E/), Dunakiliti 1843 rkm (DKI0 /47◦5941.0 beginning (unpublished data) and the end (Cs¨orgits & N, 17◦1855.1 E/, DKI1 /47◦5941.1 N, 17◦1900.5 E/, th Hufnagel 2000) of the last decade of the 20 century. DKI2 /47◦5942.4 N, 17◦1903.8 E/, DKI7 /47◦5940.6 Within a research program looking at the macroscopic N, 17◦1910.9 E/), 1839 rkm (DUF0 /47◦5825.9 N, benthic macroinvertebrates of the Danube River (Nosek 17◦2129.6 E/), 1832 rkm (DUF3 /47◦5556.5 N, 17◦24 32.9 E/), 1827.5 rkm (DUF4 /47◦5343.4 N, 17◦2645.8 & Oertel 2004), a detailed sampling program was per- ◦   ◦   ◦  formed in Szigetk¨oz in 2003. In this study, the spa- E/, DUF6 /47 53 46.6 N, 17 26 37.3 E/, DUF7 /47 43 45.9 N, 17◦2642.3 E/), Dunaremete 1825.5 rkm (DRE2 tial heterogeneity of the aquatic and semiaquatic Het- ◦   ◦   eroptera species was analysed in the area of Szigetk¨oz /47 52 51.3 N, 17 27 40.2 E/). 2. Active alluvial floodplain (HUL, 30 sampling sites): in order to identify biodiversity hotspots (sensu Myers ◦   “Mosoni” Danube, upper lock head (RAJ1 /48 00 46.9 et al. 2000) and less valuable areas. N, 17◦1300.1 E/); main canal of water supply sys- tem at Dunakiliti (VPF1 /47◦5906.0 N, 17◦1926.1 E/); “Tejfalui” side arm system: “G¨orgetegi” weir (GOR1 Material and methods /47◦5840.7 N, 17◦2100.8 E/, GOR2 /47◦5836.8 N, ◦   ◦   ◦   Szigetk¨oz, one of the two wetlands along the Hungarian 17 21 02.9 E/, GOR3 /47 58 38.2 N, 17 21 04.9 E/), ◦   ◦  part of the Danube River, is situated in the northwest part “Szigeti- or Kormos-Danube” (TEJ1 /47 57 41.3 N, 17 21  ◦   ◦   of Hungary between the main arm of the Danube River 45.1 E/, TEJ2 /47 57 43.2 N, 17 20 36.3 E/, TEJ3 ◦   ◦   (bordering Slovakia) and the Mosoni Danube down streams /47 57 23.7 N, 17 21 25.3 E/); “Cikolai” arm system: ◦   ◦   from Rajka to the city of Gy˝or. After the break through at Nagy-Ciglés (NAC1 /47 56 57.7 N, 17 23 30.5 E/), “Kis- ◦   ◦   Dévény the slope of the river bed decreases significantly, vessz˝osi” weir (CIK3 /47 56 25.7 N, 17 22 49.5 E/, CIK4 leading to an enormous bed-load and deposition of sus- /47◦5741.3 N, 17◦2146.5 E/), outlet of the side arm pended material building up the alluvial fan along with its system (CIK2 /47◦5556.3 N, 17◦2428.0 E/); “Schisler” side arm systems. The area of the Szigetk¨oz is 375 km2. oxbow lake (SCH1 /47◦5712.6 N, 17◦2121.5 E/, SCH3 Samples were taken at 81 sites in the Szigetk¨oz area /47◦5707.9 N, 17◦2136.6 E/, SCH4 /47◦5707.8 N, at three occasions, late spring (26–31 May), early summer 17◦2143.0 E/); “Csákányi” Danube (CSK0 /47◦5748.1 (22–27 July) and early autumn (8–12 September) in 2003. N, 17◦2208.0 E/, CSA1 /47◦5717.8 N, 17◦2140.0 E/,

c 2007 Institute of Zoology, Slovak Academy of Sciences 346 J.N. Nosek et al.

CSA3 /47◦5715.8 N, 17◦2148.1 E/, CSA4 /47◦5716.4 plain, protected area) and Mosoni-Danube; 3. Arm sys- N, 17◦2140.3 E/); “Denk Pál” fish ladder (HAL0 /47◦55 tems (e.g., “Zátonyi” Danube, “Csákányi” Danube, “Ciko- 54.7 N, 17◦2431.5 E/), “Bodaki” side arm system: lai” arm system, “Ásványi” arm system, “Lipóti” oxbow (BOD1 /47◦5400.2 N, 17◦2538.8 E/), outlet of the “Bo- lake, “Araki” marsh, etc.); 4. Habitats (classified by current daki” side arm system (BOD2 /47◦5348.3 N, 17◦2631.1 velocity and macrophyte density categories); 5. Sampling E/); seapage water canal at Dunaremete (DRE3 /47◦52 sites.  ◦   44.9 N, 17 27 49.6 E/); “Ásványi” side arm system: According to current velocity five categories were iden- ◦   ◦   Ásványráró harbour (ASV2 /47 50 17.7 N, 17 31 06.5 tified (R 0 = standing water <0.1 m s−1;R1=slow,0.1– ◦   ◦   E/), “V¨olgy” island (ASV3 /47 50 10.7 N, 17 32 25.1 0.5 m s−1; R 2 = middle, 0.5–1.0 m s−1;R3=strong, ◦   ◦   E/), “Halrekeszt˝o” arm (ASV5 /47 50 13.2 N, 17 30 38.4 1.0–2.0 m s−1; R 4 = very strong, > 2.0 m s−1). According ◦   ◦   E/), “Árvai” arm (ASV6 /47 49 57.3 N, 17 32 33.1 E/), to the macrophyte density (total volume of emergent and ◦   ◦   “Gombócosi” island (GOS1 /47 51 21.3 N, 17 29 39.4 submersed plants in percent of the water column) six cate- E/); “Bagaméri” side arm system: “P¨or¨os” island (BAG1 gories were distinguished (S 0 = no plant; S 1 = very rare ◦   ◦   /47 48 17.3 N, 17 34 40.5 E/), outlet of the side arm sys- (1–5%); S 2 = rare (10–25%); S 3 = middle (25–50%); S 4 ◦   ◦   tem (BAG2 /47 48 40.2 N, 17 36 40.4 E/). = dense (50–80%); S 5 = very dense (>80%)). 3. Protected area (MEN, 25 sampling sites): Seapage The index of dispersion (ID) was calculated after El- ◦   ◦   water canal at Rajka (SZC1 /48 00 44.1 N, 17 12 51.0 liot (1971). Species composition of the sampling sites was ◦   ◦   E/), and at Dunakiliti (SZC2 /47 58 46.7 N, 17 15 56.2 compared by cluster analysis using the SYN-TAX 2000 pro- ◦   ◦   E/, SZC3 /47 58 46.7 N, 17 16 02.7 E/), “Zátonyi” gram package (Podani 2001). Nomenclature was used after ◦   ◦   Danube at Dunakiliti (ZAT1 /47 58 42.1 N, 17 16 41.7 Aukema & Rieger (1999). E/, ZAT2 /47◦5755.6 N, 17◦1815.0 E/, ZAT3 /47◦57 54.1 N, 17◦1815.9 E/, ZAT8 /47◦5754.6 N, 17◦1820.1 E/, ZAD2 /47◦5755.9 N, 17◦1812.6 E/), at Dunasziget Results (ZAD1 /47◦5705.2 N, 17◦2040.1 E/), at Cikolasziget (ZAT9 /47◦5513.6 N, 17◦2155.4 E/), at Bodak (ZAT4 ◦   ◦   ◦   Total area /47 54 15.1 N, 17 23 17.3 E/, ZAT5 /47 54 07.8 N, Aquatic and/or semiaquatic Heteroptera species were 17◦2315.2 E/, ZAT6 /47◦5413.9 N, 17◦2306.0 E/, ◦   ◦   found at 53 of the 81 sampling sites (65%). There was ZAT7 /47 54 18.7 N, 17 23 01.9 E/), “Nováki” canal (NOC1 /47◦5311.7 N, 17◦2337.6 E/, NOC2 /47◦5203.0 one sampling site where only Micronecta larvae were N, 17◦2539.4 E/, NOC3 /47◦5015.8 N, 17◦2539.4 E/), found which could not be identified to species level. “Lipóti” oxbow lake (LIP2 /47◦5151.6 N, 17◦2729.0 E/, As the evaluations (cluster and correlation analyses are LIP3 /47◦5151.4 N, 17◦2718.1 E/, LIP4 /47◦5153.1 based on the occurrence and/or number of species, this N, 17◦2756.8 E/, LIP5 /47◦5149.8 N, 17◦2745.8 E/), sampling site was excluded from the analyses. At the ◦   ◦   “Zsejkei” canal at Lipót (ZSC1 /47 51 02.8 N, 17 27 40.5 remaining 52 sampling sites (code underlined in the site E/), “Araki” marsh (ARA1 /47◦5145.2 N, 17◦2131.3 E/, ◦   ◦   list) 16 aquatic and 10 semiaquatic species were sam- ARA2 and ARA3 /47 51 42.8 N, 17 21 40.3 E/). pled (Table 1). 4. Mosoni-Duna (“Mosoni” Danube, MOS, 13 sam- Ten species were very rare (38.5%), thirteen rare pling sites): Old bridge at Rajka, 120.9 rkm (RAJ2 ◦   ◦   ◦   (50.0%) and three were common (11.5%). The most /47 59 25.0 N, 17 14 17.4 E/, RAJ3 /47 59 22.2 N, 17◦1420.9 E/), Feketeerd˝o 102 rkm (FEK1 /47◦5522.7 common species in the area was Ilyocoris cimicoides N, 17◦1702.3 E/, FEK2 /47◦5526.0 N, 17◦1656.9 E/, (32.1%), followed by Micronecta scholtzi (27.2%) and FEK3 /47◦5520.8 N, 17◦1657.6 E/), Halászi, bridge Nepa cinerea (25.9%), all aquatic ones. Gerris argenta- 94 rkm (HAM1 /47◦5313.7 N, 17◦1858.7 E/), Moson- tus (13.6 %) was the most common semiaquatic species. magyaróvár 88 rkm (MMO1 /47◦5134.9 N, 17◦1707.2 The following six species were found only at one site: ◦   E/), Kimle 71.2 rkm (KML2 and KML3 /47 50 27.1 Aphelocheirus aestivalis, Callicorixa praeusta, Gerris N, 17◦2234.2 E/), 70.5 rkm (KML1 /47◦5005.7 N, ◦   ◦   asper, Microvelia pygmea, Sigara lateralis and Sigara 17 22 37.9 E/), Mecsér 48.2 rkm (MEC1 /47 47 54.9 N, fossarum (Fig. 1). 17◦2851.7 E/), Dunaszeg 33 rkm (DSG1 /47◦4533.9 N, 17◦3241.1 E/), Gy˝or-Kisbácsa12rkm(KIB1/47◦4205.1 N, 17◦3932.5 E/). Areas according to flood-prevention classification Different sampling methods were used: sampling by Considering species number, species composition and hand, hand net, triangle dredge and “kicking and sweep- relative occurrence of species there were considerable ing”. Insects were preserved in 70% alcohol. Morphology differences between areas characterised according to the and texture of the river-bed, current velocity, species com- flood-prevention classification. Five species were sam- position and density of aquatic plants were recorded at all pled in the main arm (DUF) (3 aquatic and 2 semi- sampling sites. aquatic), 17 species in the active alluvial floodplain Evaluations were based on the lists of total annual oc- (HUL) (12 aquatic and 5 semiaquatic), 24 species in currence of the species at each sampling site. The total oc- the protected area (MEN) (14 aquatic and 10 semi- currence of each species (number of sampling sites with the aquatic) and 16 species in the “Mosoni” Danube (MOS) species/total number of sampling sites) was classified into four categories: very common >50%, common 25–50%, rare (8 aquatic and 8 semiaquatic). Seven out of the 26 5–25%, very rare <5%. species (4 aquatic and 3 semiaquatic) occurred only in Spatial patterns were analysed at five different levels one area and there were only 4 species (2 aquatic and as follows: 2 semiaquatic), which lived in all four areas (Table 1). 1. Total area; 2. Areas according to the flood- According to the occurrence of the species, the prevention classification (main arm, active alluvial flood- main arm fauna differed considerably from the three Spatial pattern of water bugs 347

Table 1. Occurence of water bug species in the Szigetk¨oz area.

Species Flood prevention Arm systems Stream Plant density areas velocity DUF HUL MEN MOS TOT ARA LIP ZAT ASV TEJ CIK CSA SZV NOC R0 R1 R2 R3 R4 S0 S1 S2 S3 S4 S5

Nepa cinerea cinerea L., 1758 NEPACINE XXXX XXXX XXXX XX X XXXXXX Ranatra linearis (L., 1758) RANALINE X X X X X X X X X X X X X XXXX Aphelocheirus aestivalis aesti- APHEAEST X X X X X valis (F., 1777) Ilyocoris cimicoides cimi- ILYOCIMI XXXX XXXX XX X XXX XXXXX coides (L., 1758) Plea minutissima minutissima PLEAMINU XXXX XXXX XX XXX XXXXX Leach, 1818 NotonectaglaucaglaucaL., NOTOGLAU XX X XXX X X XXX X XX 1758 Notonecta viridis (Delcourt, NOTOVIRI X X X X X X 1909) Hesperocorixa linnaei (Fieber, HESPLINN X X X X X X X X X X X X 1848) Micronecta scholtzi (Fieber, MICNSCHOXXXXX XX XXX XXXX XXXXXX 1860) Micronecta griseola Horváth, MICNGRISXXXXX X XXX XXXX XXXXXX 1899 Micronecta minutissima (L., MICNMINU X X X X X X X X 1758) Sigara lateralis (Leach, 1817) SIGALATE X X X X X Sigara striata (L., 1758) SIGASTRI XXXX XXXXXXX XX X XXXX Sigara falleni (Fieber, 1848) SIGAFALL XXXX XXXXX X XXX XXXX Sigara fossarum (Leach, 1817) SIGA FOSS X X X X X Callicorixa praeusta praeusta CALLPRAE X X X X X (Fieber, 1848) Aquarius paludum paludum AQUAPALUXXXXX X X X XXX XXX (F., 1794) Gerris asper (Fieber, 1860) GERRASPE X X X X X X Gerris argentatus Schummel, GERRARGE XXXX XXX X X XXX XXXXX 1832 Gerris odontogaster (Zetterst- GERRODON XXX XX X XX XXX edt 1828) Gerris lacustris (L., 1758) GERRLACU XXXX X X X X X XXX Hydrometra stagnorum (L., HYDRSTAGXXXXX X XX X X X X XXX 1758) Hydrometra gracilenta HYDRGRAC X X X X X X X X X X X Horváth, 1899 Microvelia reticulata MICVRETI XXXX XXX XX X XXX XXXX (Burmeister, 1835) Microvelia pygmea (Dufour, MICVPYGM X X X X X 1833) Mesovelia furcata Mulsant et MESOFURC XXX XX X XX XXXX Rey, 1852

Total number of species 5 17 24 16 26 14 13 19 6 7 12 6 15 5 21 16 21 2 1 3 11 16 20 16 17

Explanations: DUF – main arm (Old Danube); HUL – active alluvial floodplain; MEN – protected area; MOS – Mosoni-Danube; TOT – total area; ARA – “Araki” marsh; LIP – “Lipóti” oxbow lake; ZAT – “Zátonyi” Danube; ASV – “Ásványrárói” side arm system; TEJ – “Tejfalui” side arm system; CIK – “Cikolai” side arm system; CSA – “Csákányi” Danube; SZV – seapage water canal; NOC – “Nováki” canal. others. The occurrence of Micronecta griseola was and to a lesser extent in the active alluvial flood- highest (14.3%) in the main arm. In the active al- plain. luvial floodplain and protected area, Ilyocoris cimi- Species composition of the main arm was signifi- coides (27.6% and 48% respectively) and Micronecta cantly different from all others. The values of Sørensen scholtzi (27.6% and 40% respectively) were the most similarity index (SI) are as follows: SIDUF-HUL = common species. In the “Mosoni” Danube, M. grise- 0.45, SIDUF-MEN = 0.34, SIDUF-MOS = 0.38. The ola was the most common species. About 50–60% of fauna of the Mosoni-Danube and the active allu- the species belonged to the rare category, and only vial floodplain was most similar (SIMOS-HUL = 0.79). about 10% were categorised as common. The very Fauna of the protected area was (SIMEN-MOS = 0.75, rare species occurred mainly in the protected area SIMEN-HUL = 0.73). 348 J.N. Nosek et al.

35

30

25

20

15

10

Relative occurrence (%) occurrence Relative 5

0 ILYOCIMI SIGASTRI MICVRETI SIGAFALL NOTOVIRI HESPLINN MICNMINU RANALINE MICNGRIS SIGALATE PLEAMINU NEPACINE CALLPRAE MICNSCHO APHEAEST MICVPYGM AQUAPALU SIGA FOSS SIGA HYDRSTAG NOTOGLAU GERRLACU GERRASPE MESOFURC HYDRGRAC GERRARGE GERRODON

Fig. 1. Relative occurence of water bug species in the whole area. Filled bars: aquatic species; empty bars: semiaquatic species. Abbreviations see in Table 1.

4.0

3.0

2.0

1.0

0.0 Average speciesnumber R0 R1 R2 R3 R4 Current velocity categories

Fig. 3. Correlation between average species number and current velocity. Filled circles: aquatic species; empty circles: semiaquatic Fig. 2. Dendrogram based on the fauna of the arm systems. Ab- species. breviations see in Table 1.

Arm systems Similarly to the areas categorised according to flood- low. Most species were collected at sites with standing prevention classification, considerable differences in water and moderate macrophyte density (Table 1). species number, species composition and relative oc- The average number of aquatic species decreased as currence of the species were detected between differ- current velocity increased (Spearman rank correlation, ent arm systems (Table 1). The most common species RS = −1.00, P < 0.05) while the average number of were Ilyocoris cimicoides, Micronecta scholtzi and Nepa semiaquatic species was not affected (RS = −0.30, n.s.) cinerea. Most species belonged to the rare group, except (Fig. 3). A high positive correlation was found between in the “Csákányi” Danube and “Ásványi” arm system. the average number both of the aquatic and semiaquatic Very rare species, to a great extent, were found only in species and macrophyte density (RS = 0.94, P < 0.05, the “Araki” marsh. Fig. 4). Results of the cluster analysis, based on species composition of the arm systems, shows that the “Araki” Sampling sites marsh differed considerably from the others. No other The number of aquatic species in the separate sampling clear pattern, corresponding to flood-prevention classi- sites was between 0 and 7. At two-thirds of the sampling fication or the geographical position of the arm systems, sites three or fewer species were found. The distribution was obvious (Fig. 2). of the occurrence data followed the Poisson series (ID = 1.40, d = 1.89, P < 0.05) proving that the spatial Habitats pattern of aquatic species was random. Very low species number was found in habitats where Semiaquatic species were absent from about 65% current velocity was high and macrophyte density was of the sites. The number of semiaquatic species per site Spatial pattern of water bugs 349

5.0 detected at larger scales (total area, areas according to the flood-prevention classification) and is demon- 4.0 strated well by the random spatial pattern of the 3.0 aquatic species, the Sorensen similarities and the clas- sification of the arm systems. This uniformity was also 2.0 established in the case of other taxonomic groups. A random spatial pattern was also found in the case of 1.0 Odonata species (Andrikovics et al. 2006). Investigat- ing the aquatic beetle fauna of the Szigetk¨oz, Csabai &

Average species number 0.0 Nosek (2006) found no difference between the flood- S0 S1 S2 S3 S4 S5 prevention areas. Long-term analysis (from 1990 to Plant density categories 2003) of the aquatic and semiaquatic water bugs re- Fig. 4. Correlation between average species number and macro- vealed that the fauna became improverished and more phyte density. Filled circles: aquatic species; empty circles: semi- uniform (Vásárhelyi et al. 2005). The number of species aquatic species. of small sized mussels increased with increasing similar- ity of the flood-prevention areas between 1996 and 2004 (Bódis 2006). varied between one and five. The distribution of occur- At an intermediate scale of arm systems the diver- rence data followed a negative binomial series (ID = sity of the aquatic and semiaquatic water bug fauna de- 3.23, d = 8.10, P < 0.05) indicating that the spatial pended on the habitat diversity of the arm system. The pattern of aquatic species was aggregated. fauna was poorer in the wider, deeper water bodies with Two species, namely Micronecta minutissima and higher current velocity and low macrophyte density as Sigara fossarum, were found to be rare in Hungary. Mi- in the case of the Old-Danube, “Ásványi” arm system, cronecta griseola iscommonintheSzigetk¨oz area in “Csákányi” Danube and “Tejfalui” arm. Richer fauna contrast to other parts of Hungary. was found in the standing or slowly running water bod- ies with moderate or high macrophyte density as, e.g., Discussion “Lipóti” oxbow lake, “Cikolai” arm system, seapage wa- ter canal, the marsh at Arak. The greatest diversity was Before the 1990s the hydrological regime of the water found in the “Zátonyi-Danube”. The “Zátonyi-Danube” bodies in Szigetk¨oz was governed by the Danube River. is the longest side arm with great habitat diversity, The side arm systems on the active alluvial flood plain from permanent fast flowing lotic habitats with stones were independent from each other and were to a differ- through habitats with moderate or slow flowing habi- ent extent and for various periods of time directly con- tats with moderate aquatic vegetation to permanent nected to the main arm, subject to both the Danube’s lenitic areas with abundant aquatic vegetation (Nosek water level and the bottom level of the arms. The oxbow 2005). lakes’ water supply was from ground water. They were At a smaller scale (sampling places, habitats), the directly connected with the main arm only during high spatial pattern of the species is determined by envi- flood periods. Water bodies of the protected area were ronmental factors, such as current velocity and macro- separated from the active alluvial flood plain by dykes phyte density. Aquatic Heteroptera species prefer habi- and their water also originated from the ground water. tat with standing, or slow flowing water, while the semi- From 1993 several technical measures have been aquatic species seem to be tolerant of current velocity. implemented in order to reduce the scarcity of water. The density of aquatic macrophytes positively affected The previously independent side arm systems, oxbow the occurrence of aquatic as well as semiaquatic Het- lakes – both on the active alluvial floodplain and on the eroptera species. Similarly to our results, Br¨oring & protected area – were interconnected by new artificial Niedringhaus (1988) found a positive correlation be- canals and short cuts or by dredged old natural arms tween the number of Nepomorpha species and macro- to form a water supply system. To provide this system phyte density on the East Friesian Islands of Norderney. with water by natural gravity a bottom sill was built Tolonen et al. (2003) found that vegetation density and in the abandoned main arm at river kilometre 1843, at the density of Corixidae were positively related. Csabai Dunakiliti in 1995. et al. (2005) found a significant positive correlation be- As a result of these activities the water bodies of tween the dry weight of vegetation and the number of the active alluvial floodplain and the protected area – species and the number of individuals of aquatic bee- apart from a few cases (e.g., “Araki” marsh) – are in tles and bugs in a Carex disticha dominated stand of permanent connection with each other and with the an alkalic lowland marsh. This result can be explained, abandoned main arm. The former spatial (isolation of assuming that dense macrophyte stands are associated side arm systems) and temporal (duration of inundation with a higher number of available food resources and governed by the actual water regime of the Danube) shelters. Vegetation structure clearly influences habi- barriers of the dispersion have been removed so aquatic tat selection of the pondweed bug Mesovelia furcata organisms can spread over the whole area of Szigetk¨oz. (Vásárhelyi 1989), different developmental stages of wa- The effect of this uniform water system may be terstriders (Gerridae) (Nummelin et al. 1984) and back- 350 J.N. Nosek et al. swimmers Notonecta (Bennett & Streams 1986). How- Bennett D.V. & Streams F.A. 1986. Effects of vegetation on No- ever, Svensson et al. (2000) did not find any clear influ- tonecta (Hemiptera) distribution in ponds with and without 46: ence of vegetation on habitat utilization by five back- fish. Oikos 62–69. Bíró J. 2003. Temporal-spatial pattern of true bug assemblies swimmer (Notonecta) species. (Heteroptera: Gerromorpha, Nepomorpha) in Lake Balaton. Current velocity clearly affected microhabitat as- Appl. Ecol. Environ. Res. 1: 173–181. sociation, expressed as density of Naucorids(Sites& Bódis E. 2006. A Szigetk¨oz kagyló faunájának (Corbiculidae, Willig 1991). This effect was species specific and de- Dreissenidae, Sphaeridae) egy évtized alatti változása [Long- term changes in small-sized Lamellibranchiata fauna of the pended on the density of the vegetation. Szigetk¨oz]. Acta Biol. Debr. Oecol. Hung. 14: 47–58. To date 33 aquatic and 21 semiaquatic Heteroptera Br¨oring U. & Niedringhaus R. 1988. Zur Okologie¨ aquatischer species have been found in Hungary. Almost half of Heteropteren (Hemiptera: Nepomorpha) in Kleingewassern them were collected in the Szigetk¨oz area (16 aquatic der ost friesischen Insel Norderney. Arch. Hydrobiol. 111: and 10 semiaquatic species). Micronecta minutissima 559–574. Csabai Z., Boda P., Móra A. & Tóthmérész B. 2005. Comparative was recorded in Hungary for the first time by Soós analysis of aquatic beetle and bug assemblages of sedge stands (1963), but has not been found subsequently despite ex- of an alcalic lowland marsh in Hungary. Verh. Int. Verein. tensive sampling in the same area (Bakonyi & Vásárhe- Limnol. 29: 1011–1014. lyi 1993). Another occurrence (of one specimen) was Csabai Z. & Nosek J.N. 2006. Aquatic beetle fauna of Gemenc Landscape Protection Area, South Hungary (Coleoptera: Hy- reported by Bíró (2003) near Lake Balaton. This dradephaga, Hydrophiloidea). Acta Biol. Debr. Oecol. Hung. species was found in large numbers during a study 14: 67–76. into macroinvertebrate biodiversity of the Hungarian Cs¨orgits G. & Hufnagel L. 2000. Bioindikáció vízi gerincte- Danube section in 2002 at Tát in a side arm of the lenekkel a Dunában. 4. Heteroptera fajegy¨uttesek hasonlósági mintázata a Dunán [Bioindication by macroinvertebrates in Danube near Esztergom (Nosek & Oertel 2004). The the Danube. 4. Similarity patterns of Heteroptera communi- species Microvelia pygmaea (its northernmost site in ties in the Danube]. Hidrológiai K¨ozl¨ony 80: 288–290. Central Europe) and Sigara fossarum (it was reported Elliot J.M. 1971. Statistical Analysis of Samples of Benthic Inver- from Hungary from this area by Bakonyi 1990 a decade tebrates. Freshwater Biological Association, Scientific Publ., No. 25, 144 pp. ago, and has been found since at several places in Hun- Myers N., Mittermeier R.A., Mittermeier C.G., da Fonseca gary by different specialists) are rare in Hungary and G.A.B. & Kent J. 2000. Biodiversity hotspots for conserva- deserve a short note. In contrast to other parts of Hun- tion priorities. Nature 403: 853–858. gary, Micronecta griseola is common in the Szigetk¨oz Nosek J.N. 1996. Untersuchung der wirbellosen Wassermakro- fauna in der Kleinen Sch¨uttinsel (Szigetk¨oz), pp. 255–260. area. These data indicate the value of the Szigetk¨oz In: Limnolog. Ber. der 31. IAD-Konferenz, Baja/Ungarn. area in general, as well as in connection with the Het- Nosek J. 2005. A vízi gerinctelen makrofauna változása a eroptera fauna. The marsh at Arak is categorised as Szigetk¨ozben az utóbbi tíz évben [Changes of the macroinver- “highly protected” by law. The marsh is of high faunis- tebrate fauna in the wetland area of the hungarian Danube, Szigetk¨oz in the past ten years]. Hidrológiai K¨ozl¨ony 85: 105– tic value from the point of view of both aquatic beetles 107. (Csabai & Nosek 2006) and Heteroptera. Nosek J.N. & Oertel N. 2004. Makrogerinctelenek biodiverzitás vizsgálata a magyar Duna-szakaszon. I. Bevezetés és el˝ozetes eredmények [Macroinvertebrate biodiversity investigations in Acknowledgements the Hungarian Section of the Danube. I. Introduction and preliminary results]. Hidrológiai K¨ozl¨ony 84: 104–107 The research was supported by the Hungarian Science Nummelin M., Vepsalainen K. & Spence J.R. 1984. Habitat par- Found OTKA (No. T 037468). We are grateful to Kelényiné titioning among developmental stages of waterstriders (Hete- 42: Welner Irma for the laboratory work. roptera: Gerridae). Oikos 267–275. Podani J. 2001. SYN-TAX 2000. Computer Programs for Data Analysis in Ecology and Systematics. User’s Manual. Scientia References Publishing, Budapest, 53 pp. Sites R.W. & Willig M.R. 1991. Microhabitat associations of three sympatric species of Naucoridae (Insecta: Hemiptera). Envi- Andrikovics S., Nosek J.N. & Oertel N. 2006. Szitak¨ot˝o (Odonata) ron. Entomol. 20: 127–134. lárvavizsgálatok a Szigetk¨ozben [The Odonata fauna of the Soós Á. 1963. Poloskák VIII. – Heteroptera VIII, pp. 1–48. In: Szigetk¨oz on the basis of larval investigations]. Acta Biol. Székessy V. (ed.), Fauna Regni Hungariae 17(8). Debr. Oecol. Hung. 14: 9–19. Svensson B.G., Tallmark B. & Pettersson E. 2000. Habitat het- Ambrus A., Bánkúti K., Csányi B., Juhász P. & Kovács T. erogeneity, coexistence and habitat utilization in five back- 1995. Újabb adatok az Aphelocheirus aestivalis Fabricius, swimmer species (Notonecta spp.: Hemiptera, Notonectidae). 1794 (Heteroptera, Naucoridae) magyarországi elterjedéséhez Aquatic Insects 22: 81–98. [New data to the distribution of Aphelocheirus aestivalis Tolonen K.T., Hamalainen H., Holopainen I.J., Mikkonen K. & Fabricius, 1794 (Heteroptera, Naucoridae) in Hungary]. Folia Karjalainen J. 2003. Body size and substrate association of Entomol. Hung. 56: 223–256. littoral insects in relation to vegetation structure. Hydrobi- Aukema B. & Rieger C. 1999. Catalogue of the Heteroptera of ologia 499: 179–190. the Palearctic Region. Netherland Entomol. Soc. 3: 1–577. Vásárhelyi T. 1989. Microhabitat preference of the pondweed bug Bakonyi G. 1990. Sigara fossarum, hazánk faunájában új Mesovelia furcata (Heteroptera: Mesoveliidae). Folia Ento- vízipoloska a Szigetk¨ozb˝ol (Heteroptera) [Sigara fossarum, mol. Hung. 50: 165–168. a new waterboatmen species in the Hungarian fauna (Het- Vásárhelyi T., Bakonyi G. & Nosek J. 2005. A vízipoloska eroptera)]. Folia Entomol. Hung. 51: 163. fauna évtizedes lépték¨u változása a Szigetk¨ozben [Long-term Bakonyi G. & Vásárhelyi T. 1993. Aquatic and semiaquatic bugs changes in the aquatic Heteroptera fauna of the Szigetk¨oz, of the B¨ukk National Park (Heteroptera: Nepomorpha and North Hungary]. Acta Biol. Debr. Oecol. Hung. 13: 249–258. Gerromorpha), pp. 65–67. In: Mahunka S. (ed.), The Fauna of the B¨ukk National Park, Magyar Természettudományi Received May 28, 2006 Múzeum, Budapest. Accepted November 15, 2006