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 Vásárhelyi2, Gábor Bakonyi3 & Nándor Oertel1 1
Hungarian Danube Research Station of HAS, Jávorka S. u. 14, H-2131 G¨ od, Hungary; e-mail:
[email protected] Hungarian Natural History Museum, Baross u. 13, H-1088 Budapest, Hungary 3 SzIU Department of Zoology and Ecology, Páter K. u. 1, H-2100 G¨ od¨ oll˝ o, Hungary 2
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 There are very few data on the aquatic and semiaquatic bug (Heteroptera: Nepomorpha and Gerromorpha) fauna of the Szigetk¨ oz arm system of the Danube River. Only sporadic faunistical data are available concerning the occurrence of some species (Bakonyi 1990; Ambrus et al. 1995; Nosek 1996). Systematic sampling programmes have been carried out only twice, at the beginning (unpublished data) and the end (Cs¨ orgits & Hufnagel 2000) of the last decade of the 20th century. Within a research program looking at the macroscopic benthic macroinvertebrates of the Danube River (Nosek & Oertel 2004), a detailed sampling program was performed in Szigetk¨ oz in 2003. In this study, the spatial heterogeneity of the aquatic and semiaquatic Heteroptera species was analysed in the area of Szigetk¨ oz in order to identify biodiversity hotspots (sensu Myers et al. 2000) and less valuable areas. Material and methods Szigetk¨ oz, one of the two wetlands along the Hungarian part of the Danube River, is situated in the northwest part of Hungary between the main arm of the Danube River (bordering Slovakia) and the Mosoni Danube down streams from Rajka to the city of Gy˝ or. After the break through at Dévény the slope of the river bed decreases significantly, leading to an enormous bed-load and deposition of suspended material building up the alluvial fan along with its side arm systems. The area of the Szigetk¨ oz is 375 km2 . Samples were taken at 81 sites in the Szigetk¨ oz area at three occasions, late spring (26–31 May), early summer (22–27 July) and early autumn (8–12 September) in 2003.
c 2007 Institute of Zoology, Slovak Academy of Sciences
Sampling sites can be identified by the name of the water body or the nearest site, with the aid of the river kilometre mark (rkm) and the code of the site. Sites were selected in order to ensure habitat diversity was as high as possible. The sites are as follows: ¨ 1. Danube main arm, (Oreg-Duna, Old Danube, DUF), abandoned main arm, 13 sampling sites): Dunakiliti 1845 rkm (DKI4 /47◦ 59 41.0 N, 17◦ 18 51.0 E/, DKI5 /47◦ 59 40.3 N, 17◦ 18 49.1 E/, DKI6 /47◦ 59 40.0 N, 17◦ 18 46.7 E/), Dunakiliti 1843 rkm (DKI0 /47◦ 59 41.0 N, 17◦ 18 55.1 E/, DKI1 /47◦ 59 41.1 N, 17◦ 19 00.5 E/, DKI2 /47◦ 59 42.4 N, 17◦ 19 03.8 E/, DKI7 /47◦ 59 40.6 N, 17◦ 19 10.9 E/), 1839 rkm (DUF0 /47◦ 58 25.9 N, 17◦ 21 29.6 E/), 1832 rkm (DUF3 /47◦ 55 56.5 N, 17◦ 24 32.9 E/), 1827.5 rkm (DUF4 /47◦ 53 43.4 N, 17◦ 26 45.8 E/, DUF6 /47◦ 53 46.6 N, 17◦ 26 37.3 E/, DUF7 /47◦ 43 45.9 N, 17◦ 26 42.3 E/), Dunaremete 1825.5 rkm (DRE2 /47◦ 52 51.3 N, 17◦ 27 40.2 E/). 2. Active alluvial floodplain (HUL, 30 sampling sites): “Mosoni” Danube, upper lock head (RAJ1 /48◦ 00 46.9 N, 17◦ 13 00.1 E/); main canal of water supply system at Dunakiliti (VPF1 /47◦ 59 06.0 N, 17◦ 19 26.1 E/); “Tejfalui” side arm system: “G¨ orgetegi” weir (GOR1 /47◦ 58 40.7 N, 17◦ 21 00.8 E/, GOR2 /47◦ 58 36.8 N, 17◦ 21 02.9 E/, GOR3 /47◦ 58 38.2 N, 17◦ 21 04.9 E/), “Szigeti- or Kormos-Danube” (TEJ1 /47◦ 57 41.3 N, 17◦ 21 45.1 E/, TEJ2 /47◦ 57 43.2 N, 17◦ 20 36.3 E/, TEJ3 /47◦ 57 23.7 N, 17◦ 21 25.3 E/); “Cikolai” arm system: Nagy-Ciglés (NAC1 /47◦ 56 57.7 N, 17◦ 23 30.5 E/), “Kisvessz˝ osi” weir (CIK3 /47◦ 56 25.7 N, 17◦ 22 49.5 E/, CIK4 ◦ /47 57 41.3 N, 17◦ 21 46.5 E/), outlet of the side arm system (CIK2 /47◦ 55 56.3 N, 17◦ 24 28.0 E/); “Schisler” oxbow lake (SCH1 /47◦ 57 12.6 N, 17◦ 21 21.5 E/, SCH3 /47◦ 57 07.9 N, 17◦ 21 36.6 E/, SCH4 /47◦ 57 07.8 N, 17◦ 21 43.0 E/); “Csákányi” Danube (CSK0 /47◦ 57 48.1 N, 17◦ 22 08.0 E/, CSA1 /47◦ 57 17.8 N, 17◦ 21 40.0 E/,
J.N. Nosek et al.
346 CSA3 /47◦ 57 15.8 N, 17◦ 21 48.1 E/, CSA4 /47◦ 57 16.4 N, 17◦ 21 40.3 E/); “Denk Pál” fish ladder (HAL0 /47◦ 55 54.7 N, 17◦ 24 31.5 E/), “Bodaki” side arm system: (BOD1 /47◦ 54 00.2 N, 17◦ 25 38.8 E/), outlet of the “Bodaki” side arm system (BOD2 /47◦ 53 48.3 N, 17◦ 26 31.1 E/); seapage water canal at Dunaremete (DRE3 /47◦ 52 44.9 N, 17◦ 27 49.6 E/); “Ásványi” side arm system: Ásványráró harbour (ASV2 /47◦ 50 17.7 N, 17◦ 31 06.5 E/), “V¨ olgy” island (ASV3 /47◦ 50 10.7 N, 17◦ 32 25.1 E/), “Halrekeszt˝ o” arm (ASV5 /47◦ 50 13.2 N, 17◦ 30 38.4 E/), “Árvai” arm (ASV6 /47◦ 49 57.3 N, 17◦ 32 33.1 E/), “Gombócosi” island (GOS1 /47◦ 51 21.3 N, 17◦ 29 39.4 E/); “Bagaméri” side arm system: “P¨ or¨ os” island (BAG1 /47◦ 48 17.3 N, 17◦ 34 40.5 E/), outlet of the side arm system (BAG2 /47◦ 48 40.2 N, 17◦ 36 40.4 E/). 3. Protected area (MEN, 25 sampling sites): Seapage water canal at Rajka (SZC1 /48◦ 00 44.1 N, 17◦ 12 51.0 E/), and at Dunakiliti (SZC2 /47◦ 58 46.7 N, 17◦ 15 56.2 E/, SZC3 /47◦ 58 46.7 N, 17◦ 16 02.7 E/), “Zátonyi” Danube at Dunakiliti (ZAT1 /47◦ 58 42.1 N, 17◦ 16 41.7 E/, ZAT2 /47◦ 57 55.6 N, 17◦ 18 15.0 E/, ZAT3 /47◦ 57 54.1 N, 17◦ 18 15.9 E/, ZAT8 /47◦ 57 54.6 N, 17◦ 18 20.1 E/, ZAD2 /47◦ 57 55.9 N, 17◦ 18 12.6 E/), at Dunasziget (ZAD1 /47◦ 57 05.2 N, 17◦ 20 40.1 E/), at Cikolasziget (ZAT9 /47◦ 55 13.6 N, 17◦ 21 55.4 E/), at Bodak (ZAT4 /47◦ 54 15.1 N, 17◦ 23 17.3 E/, ZAT5 /47◦ 54 07.8 N, 17◦ 23 15.2 E/, ZAT6 /47◦ 54 13.9 N, 17◦ 23 06.0 E/, ZAT7 /47◦ 54 18.7 N, 17◦ 23 01.9 E/), “Nováki” canal (NOC1 /47◦ 53 11.7 N, 17◦ 23 37.6 E/, NOC2 /47◦ 52 03.0 N, 17◦ 25 39.4 E/, NOC3 /47◦ 50 15.8 N, 17◦ 25 39.4 E/), “Lipóti” oxbow lake (LIP2 /47◦ 51 51.6 N, 17◦ 27 29.0 E/, LIP3 /47◦ 51 51.4 N, 17◦ 27 18.1 E/, LIP4 /47◦ 51 53.1 N, 17◦ 27 56.8 E/, LIP5 /47◦ 51 49.8 N, 17◦ 27 45.8 E/), “Zsejkei” canal at Lipót (ZSC1 /47◦ 51 02.8 N, 17◦ 27 40.5 E/), “Araki” marsh (ARA1 /47◦ 51 45.2 N, 17◦ 21 31.3 E/, ARA2 and ARA3 /47◦ 51 42.8 N, 17◦ 21 40.3 E/). 4. Mosoni-Duna (“Mosoni” Danube, MOS, 13 sampling sites): Old bridge at Rajka, 120.9 rkm (RAJ2 /47◦ 59 25.0 N, 17◦ 14 17.4 E/, RAJ3 /47◦ 59 22.2 N, 17◦ 14 20.9 E/), Feketeerd˝ o 102 rkm (FEK1 /47◦ 55 22.7 ◦ N, 17 17 02.3 E/, FEK2 /47◦ 55 26.0 N, 17◦ 16 56.9 E/, FEK3 /47◦ 55 20.8 N, 17◦ 16 57.6 E/), Halászi, bridge 94 rkm (HAM1 /47◦ 53 13.7 N, 17◦ 18 58.7 E/), Mosonmagyaróvár 88 rkm (MMO1 /47◦ 51 34.9 N, 17◦ 17 07.2 E/), Kimle 71.2 rkm (KML2 and KML3 /47◦ 50 27.1 N, 17◦ 22 34.2 E/), 70.5 rkm (KML1 /47◦ 50 05.7 N, 17◦ 22 37.9 E/), Mecsér 48.2 rkm (MEC1 /47◦ 47 54.9 N, 17◦ 28 51.7 E/), Dunaszeg 33 rkm (DSG1 /47◦ 45 33.9 N, 17◦ 32 41.1 E/), Gy˝ or-Kisbácsa 12 rkm (KIB1 /47◦ 42 05.1 ◦ N, 17 39 32.5 E/). Different sampling methods were used: sampling by hand, hand net, triangle dredge and “kicking and sweeping”. Insects were preserved in 70% alcohol. Morphology and texture of the river-bed, current velocity, species composition and density of aquatic plants were recorded at all sampling sites. Evaluations were based on the lists of total annual occurrence of the species at each sampling site. The total occurrence of each species (number of sampling sites with the species/total number of sampling sites) was classified into four categories: very common >50%, common 25–50%, rare 5–25%, very rare 80%)). The index of dispersion (ID) was calculated after Elliot (1971). Species composition of the sampling sites was compared by cluster analysis using the SYN-TAX 2000 program package (Podani 2001). Nomenclature was used after Aukema & Rieger (1999).
Results Total area Aquatic and/or semiaquatic Heteroptera species were found at 53 of the 81 sampling sites (65%). There was one sampling site where only Micronecta larvae were found which could not be identified to species level. As the evaluations (cluster and correlation analyses are based on the occurrence and/or number of species, this sampling site was excluded from the analyses. At the remaining 52 sampling sites (code underlined in the site list) 16 aquatic and 10 semiaquatic species were sampled (Table 1). Ten species were very rare (38.5%), thirteen rare (50.0%) and three were common (11.5%). The most common species in the area was Ilyocoris cimicoides (32.1%), followed by Micronecta scholtzi (27.2%) and Nepa cinerea (25.9%), all aquatic ones. Gerris argentatus (13.6 %) was the most common semiaquatic species. The following six species were found only at one site: Aphelocheirus aestivalis, Callicorixa praeusta, Gerris asper, Microvelia pygmea, Sigara lateralis and Sigara fossarum (Fig. 1). Areas according to flood-prevention classification Considering species number, species composition and relative occurrence of species there were considerable differences between areas characterised according to the flood-prevention classification. Five species were sampled in the main arm (DUF) (3 aquatic and 2 semiaquatic), 17 species in the active alluvial floodplain (HUL) (12 aquatic and 5 semiaquatic), 24 species in the protected area (MEN) (14 aquatic and 10 semiaquatic) and 16 species in the “Mosoni” Danube (MOS) (8 aquatic and 8 semiaquatic). Seven out of the 26 species (4 aquatic and 3 semiaquatic) occurred only in one area and there were only 4 species (2 aquatic and 2 semiaquatic), which lived in all four areas (Table 1). According to the occurrence of the species, the 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.
Nepa cinerea cinerea L., 1758 Ranatra linearis (L., 1758) Aphelocheirus aestivalis aestivalis (F., 1777) Ilyocoris cimicoides cimicoides (L., 1758) Plea minutissima minutissima Leach, 1818 Notonecta glauca glauca L., 1758 Notonecta viridis (Delcourt, 1909) Hesperocorixa linnaei (Fieber, 1848) Micronecta scholtzi (Fieber, 1860) Micronecta griseola Horváth, 1899 Micronecta minutissima (L., 1758) Sigara lateralis (Leach, 1817) Sigara striata (L., 1758) Sigara falleni (Fieber, 1848) Sigara fossarum (Leach, 1817) Callicorixa praeusta praeusta (Fieber, 1848) Aquarius paludum paludum (F., 1794) Gerris asper (Fieber, 1860) Gerris argentatus Schummel, 1832 Gerris odontogaster (Zetterstedt 1828) Gerris lacustris (L., 1758) Hydrometra stagnorum (L., 1758) Hydrometra gracilenta Horváth, 1899 Microvelia reticulata (Burmeister, 1835) Microvelia pygmea (Dufour, 1833) Mesovelia furcata Mulsant et Rey, 1852 Total number of species
S5
S4
S3
S2
S0 S1
Plant density
R2 R3 R4
R1
R0
Stream velocity
ZAT ASV TEJ CIK CSA SZV NOC
LIP
Arm systems
ARA
TOT
MOS
MEN
Flood prevention areas DUF HUL
Species
NEPACINE X X X X RANALINE X X X X APHEAEST X X
X X X X X X X
X X X X X X X X
X X X X X X X
X X X X X X X X X X X
ILYOCIMI
X X X X
X X X X
X X
X X X
X X X X X
PLEAMINU
X X X X
X X X X
X X
X X X
X X X X X
NOTOGLAU
X X
X
X X X
X
X X X
X
NOTOVIRI
X X
X
X
HESPLINN
X
X
X X X
X
MICNSCHO X X X X X
X X
X X X
MICNGRIS
X X X X X
MICNMINU
X
SIGALATE SIGASTRI SIGAFALL SIGA FOSS CALLPRAE
X X X X X X X X X
X
X
X X X X X X
X X X X
GERRODON
X X X
X X
GERRLACU X X X X HYDRSTAG X X X X X
X X
MICVRETI
X X X X
MICVPYGM
X
X
MESOFURC
X X X
5 17 24 16 26
X X X
X
X
X
X X X
X
X X X
X
X X
X X X X X X
X X X X
X X X X X X X X
X X X X X X X X X
X X X X X X X X X X X
X
X X X
X X X
X X
X X X X
X X X X X X
X
X X
X X X
X X
X X
X X
X
X
X
X
X X X
X
X
X X X
X X
X X X X
X X
X X X X X X X X X X X X X X X X
GERRASPE GERRARGE
X X X
X X X
X X X
X
AQUAPALU X X X X X
HYDRGRAC
X
X
X X X X X X X
X
X
14 13 19 6 7 12 6 15 5
X X X X X X X X
X
X X X X X
X X
21 16 21 2 1
X X X X
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 highest (14.3%) in the main arm. In the active alluvial floodplain and protected area, Ilyocoris cimicoides (27.6% and 48% respectively) and Micronecta scholtzi (27.6% and 40% respectively) were the most common species. In the “Mosoni” Danube, M. griseola was the most common species. About 50–60% of the species belonged to the rare category, and only about 10% were categorised as common. The very rare species occurred mainly in the protected area
and to a lesser extent in the active alluvial floodplain. Species composition of the main arm was significantly different from all others. The values of Sørensen similarity index (SI) are as follows: SIDUF-HUL = 0.45, SIDUF-MEN = 0.34, SIDUF-MOS = 0.38. The fauna of the Mosoni-Danube and the active alluvial floodplain was most similar (SIMOS-HUL = 0.79). Fauna of the protected area was (SIMEN-MOS = 0.75, SIMEN-HUL = 0.73).
J.N. Nosek et al.
348 35
30
Relative occurrence (%)
25
20
15
10
5
MICVPYGM
GERRASPE
CALLPRAE
SIGALATE
SIGA FOSS
APHEAEST
NOTOVIRI
MICNMINU
HYDRGRAC
HESPLINN
GERRLACU
AQUAPALU
GERRODON
HYDRSTAG
NOTOGLAU
SIGAFALL
MESOFURC
MICVRETI
RANALINE
GERRARGE
SIGASTRI
MICNGRIS
PLEAMINU
NEPACINE
ILYOCIMI
MICNSCHO
0
Average species number
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 R0
Fig. 2. Dendrogram based on the fauna of the arm systems. Abbreviations see in Table 1.
Arm systems Similarly to the areas categorised according to floodprevention classification, considerable differences in species number, species composition and relative occurrence of the species were detected between different arm systems (Table 1). The most common species were Ilyocoris cimicoides, Micronecta scholtzi and Nepa cinerea. Most species belonged to the rare group, except in the “Csákányi” Danube and “Ásványi” arm system. Very rare species, to a great extent, were found only in the “Araki” marsh. Results of the cluster analysis, based on species composition of the arm systems, shows that the “Araki” marsh differed considerably from the others. No other clear pattern, corresponding to flood-prevention classification or the geographical position of the arm systems, was obvious (Fig. 2). Habitats Very low species number was found in habitats where current velocity was high and macrophyte density was
R1 R2 R3 R4 Current velocity categories
Fig. 3. Correlation between average species number and current velocity. Filled circles: aquatic species; empty circles: semiaquatic species.
low. Most species were collected at sites with standing water and moderate macrophyte density (Table 1). The average number of aquatic species decreased as current velocity increased (Spearman rank correlation, RS = −1.00, P < 0.05) while the average number of semiaquatic species was not affected (RS = −0.30, n.s.) (Fig. 3). A high positive correlation was found between the average number both of the aquatic and semiaquatic species and macrophyte density (RS = 0.94, P < 0.05, Fig. 4). Sampling sites The number of aquatic species in the separate sampling sites was between 0 and 7. At two-thirds of the sampling sites three or fewer species were found. The distribution of the occurrence data followed the Poisson series (ID = 1.40, d = 1.89, P < 0.05) proving that the spatial pattern of aquatic species was random. Semiaquatic species were absent from about 65% of the sites. The number of semiaquatic species per site
Average species number
Spatial pattern of water bugs
349
5.0 4.0 3.0 2.0 1.0 0.0 S0
S1 S2 S3 S4 Plant density categories
S5
Fig. 4. Correlation between average species number and macrophyte density. Filled circles: aquatic species; empty circles: semiaquatic species.
varied between one and five. The distribution of occurrence data followed a negative binomial series (ID = 3.23, d = 8.10, P < 0.05) indicating that the spatial pattern of aquatic species was aggregated. Two species, namely Micronecta minutissima and Sigara fossarum, were found to be rare in Hungary. Micronecta griseola is common in the Szigetk¨ oz area in contrast to other parts of Hungary. Discussion Before the 1990s the hydrological regime of the water bodies in Szigetk¨ oz was governed by the Danube River. The side arm systems on the active alluvial flood plain were independent from each other and were to a different extent and for various periods of time directly connected to the main arm, subject to both the Danube’s water level and the bottom level of the arms. The oxbow lakes’ water supply was from ground water. They were directly connected with the main arm only during high flood periods. Water bodies of the protected area were separated from the active alluvial flood plain by dykes and their water also originated from the ground water. From 1993 several technical measures have been implemented in order to reduce the scarcity of water. The previously independent side arm systems, oxbow lakes – both on the active alluvial floodplain and on the protected area – were interconnected by new artificial canals and short cuts or by dredged old natural arms to form a water supply system. To provide this system with water by natural gravity a bottom sill was built in the abandoned main arm at river kilometre 1843, at Dunakiliti in 1995. As a result of these activities the water bodies of the active alluvial floodplain and the protected area – apart from a few cases (e.g., “Araki” marsh) – are in permanent connection with each other and with the abandoned main arm. The former spatial (isolation of side arm systems) and temporal (duration of inundation governed by the actual water regime of the Danube) barriers of the dispersion have been removed so aquatic organisms can spread over the whole area of Szigetk¨ oz. The effect of this uniform water system may be
detected at larger scales (total area, areas according to the flood-prevention classification) and is demonstrated well by the random spatial pattern of the aquatic species, the Sorensen similarities and the classification of the arm systems. This uniformity was also established in the case of other taxonomic groups. A random spatial pattern was also found in the case of Odonata species (Andrikovics et al. 2006). Investigating the aquatic beetle fauna of the Szigetk¨ oz, Csabai & Nosek (2006) found no difference between the floodprevention areas. Long-term analysis (from 1990 to 2003) of the aquatic and semiaquatic water bugs revealed that the fauna became improverished and more uniform (Vásárhelyi et al. 2005). The number of species of small sized mussels increased with increasing similarity of the flood-prevention areas between 1996 and 2004 (Bódis 2006). At an intermediate scale of arm systems the diversity of the aquatic and semiaquatic water bug fauna depended on the habitat diversity of the arm system. The fauna was poorer in the wider, deeper water bodies with higher current velocity and low macrophyte density as in the case of the Old-Danube, “Ásványi” arm system, “Csákányi” Danube and “Tejfalui” arm. Richer fauna was found in the standing or slowly running water bodies with moderate or high macrophyte density as, e.g., “Lipóti” oxbow lake, “Cikolai” arm system, seapage water canal, the marsh at Arak. The greatest diversity was found in the “Zátonyi-Danube”. The “Zátonyi-Danube” is the longest side arm with great habitat diversity, from permanent fast flowing lotic habitats with stones through habitats with moderate or slow flowing habitats with moderate aquatic vegetation to permanent lenitic areas with abundant aquatic vegetation (Nosek 2005). At a smaller scale (sampling places, habitats), the spatial pattern of the species is determined by environmental factors, such as current velocity and macrophyte density. Aquatic Heteroptera species prefer habitat with standing, or slow flowing water, while the semiaquatic species seem to be tolerant of current velocity. The density of aquatic macrophytes positively affected the occurrence of aquatic as well as semiaquatic Heteroptera species. Similarly to our results, Br¨ oring & Niedringhaus (1988) found a positive correlation between the number of Nepomorpha species and macrophyte density on the East Friesian Islands of Norderney. Tolonen et al. (2003) found that vegetation density and the density of Corixidae were positively related. Csabai et al. (2005) found a significant positive correlation between the dry weight of vegetation and the number of species and the number of individuals of aquatic beetles and bugs in a Carex disticha dominated stand of an alkalic lowland marsh. This result can be explained, assuming that dense macrophyte stands are associated with a higher number of available food resources and shelters. Vegetation structure clearly influences habitat selection of the pondweed bug Mesovelia furcata (Vásárhelyi 1989), different developmental stages of waterstriders (Gerridae) (Nummelin et al. 1984) and back-
350 swimmers Notonecta (Bennett & Streams 1986). However, Svensson et al. (2000) did not find any clear influence of vegetation on habitat utilization by five backswimmer (Notonecta) species. Current velocity clearly affected microhabitat association, expressed as density of Naucorids (Sites & Willig 1991). This effect was species specific and depended on the density of the vegetation. To date 33 aquatic and 21 semiaquatic Heteroptera species have been found in Hungary. Almost half of them were collected in the Szigetk¨ oz area (16 aquatic and 10 semiaquatic species). Micronecta minutissima was recorded in Hungary for the first time by Soós (1963), but has not been found subsequently despite extensive sampling in the same area (Bakonyi & Vásárhelyi 1993). Another occurrence (of one specimen) was reported by Bíró (2003) near Lake Balaton. This species was found in large numbers during a study into macroinvertebrate biodiversity of the Hungarian Danube section in 2002 at Tát in a side arm of the Danube near Esztergom (Nosek & Oertel 2004). The species Microvelia pygmaea (its northernmost site in Central Europe) and Sigara fossarum (it was reported from Hungary from this area by Bakonyi 1990 a decade ago, and has been found since at several places in Hungary by different specialists) are rare in Hungary and deserve a short note. In contrast to other parts of Hungary, Micronecta griseola is common in the Szigetk¨ oz area. These data indicate the value of the Szigetk¨oz area in general, as well as in connection with the Heteroptera fauna. The marsh at Arak is categorised as “highly protected” by law. The marsh is of high faunistic value from the point of view of both aquatic beetles (Csabai & Nosek 2006) and Heteroptera. Acknowledgements The research was supported by the Hungarian Science Found OTKA (No. T 037468). We are grateful to Kelényiné Welner Irma for the laboratory work. References Andrikovics S., Nosek J.N. & Oertel N. 2006. Szitak¨ ot˝ o (Odonata) lárvavizsgálatok a Szigetk¨ ozben [The Odonata fauna of the Szigetk¨ oz on the basis of larval investigations]. Acta Biol. Debr. Oecol. Hung. 14: 9–19. Ambrus A., Bánkúti K., Csányi B., Juhász P. & Kovács T. 1995. Újabb adatok az Aphelocheirus aestivalis Fabricius, 1794 (Heteroptera, Naucoridae) magyarországi elterjedéséhez [New data to the distribution of Aphelocheirus aestivalis Fabricius, 1794 (Heteroptera, Naucoridae) in Hungary]. Folia Entomol. Hung. 56: 223–256. Aukema B. & Rieger C. 1999. Catalogue of the Heteroptera of the Palearctic Region. Netherland Entomol. Soc. 3: 1–577. Bakonyi G. 1990. Sigara fossarum, hazánk faunájában új vízipoloska a Szigetk¨ ozb˝ ol (Heteroptera) [Sigara fossarum, a new waterboatmen species in the Hungarian fauna (Heteroptera)]. Folia Entomol. Hung. 51: 163. Bakonyi G. & Vásárhelyi T. 1993. Aquatic and semiaquatic bugs of the B¨ ukk National Park (Heteroptera: Nepomorpha and Gerromorpha), pp. 65–67. In: Mahunka S. (ed.), The Fauna of the B¨ ukk National Park, Magyar Természettudományi Múzeum, Budapest.
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