## DRAGONFLIES (ODONATA( AND AQUATIC BUGS (HETEROPTERA AQUATICA) OF STAGNANT WATERS IN THE REGION OF THE GABCIKOVO PROJECT

####
Eva BULANKOVA

Zoological Institute, Faculty of Natural Sciences, Comenius University, Mlynska dolina, 84215 Bratislava, SLOVAKIA

CONCLUSIONS Results of dragonflies and aquatic bugs biomonitoring on 8 localities, in the region of the Gabcikovo project, in 1993-1994 indicated the following changes: The localities of Dunajske Kriviny and Istragov are the most influenced by drying up. An improvement of the situation occurred in the localities of Kralovska luka and Bodiky, which was manifested by a greater qualitative-quantitative spectrum of the observed species. The richest species spectrum of dragonflies and aquatic bugs was found in the locality of Sporna Sihot. The locality of Stary les is also scarce from the faunistic point of view.

#### INTRODUCTION

The research of dragonflies and aquatic bugs was performed in 1993 and 1994, on 8 monitoring localities influenced by the Gabcikovo project. Dragonflies were studied on Zitny ostrov island also in the past ([12], [3], [11], [9], [1], [8]), where the authors recorded an occurrence of more rare and threatened species in this territory. Aquatic bugs were not studied here until now.

#### MATERIAL AND METHODS

We were collecting sample material in one- to two-month intervals, during the vegetation period in 1993 and 1994. We started with the collection of samples in the monitoring areas of Stary les and Cicov only in July 1993, which also influenced the results of the research in these areas. The samples were collected by dragging the submersed vegetation and water level with a hydrobiological net, and in 1993 also with a benthometer. Imagoes of dragonflies were obtained by dragging of the shore stand. The material was fixed in 4% formaline and the imagoes of dragonflies in 80% alcohol, in which also the collected material was also deposited.

#### RESULTS AND DISCUSSION

The species spectrum of dragonflies and aquatic bugs is given in Tables 1 and 2, together with the degree of dominance in single localities. In total we recorded 26 species of dragonflies and 20 species of aquatic bugs in the observed territory, which represents about 40% of the dragonflies and aquatic bugs fauna of Slovakia. The bioindication characteristics of dragonflies are relatively well known. Castella [4] included the dragonfly Ischnura elegans among the indicators of stability. Straka [10] states, that the species Platycnemis pennipes indicates relatively well preserved biotopes. Therefore, we included both these species among the indicators of stability. Species of genus Lestes bear are also resistant to temporary drying of the biotope, because their development is relatively short, and finishes before the summer drying of aquatic biotopes [5]. For this reason we included the species of the genus Lestes among the indicators for drying conditions. Rare and threatened species of dragonflies (in sense of David [7]) are mentioned according to their occurrence in individually presented localities.

#### Ostrov Kopac - Plesiopotamal

In 1993 we recorded representatives of the family Lestidae, which are indicators of the drying of localities (Table 1, Fig. 1). A different situation arose in 1994, when the dragonfly Platycnemis pennipes (Platycnemidae), which occurred in relatively preserved biotopes, dominated this area [10]. The larva of this species are rheophilous [12], and sensitive to water pollution [6]. The presence of the species of the genus Sympetrum, as well as the dominance of the bugs Plea minutissima and Ilyocoris cimicoides (Table 2) documents the visible eutrophication of vegetation to a rich, warm aquatic biotope.

#### Ostrov Kopac - Gravel-ground

Apart from eurytopic species, which we also recorded in the previous year, we caught the dragonfly Calopteryx splendens in 1994, which was recorded here by Majzlan [9].

#### Cunovo - Ostrovne lucky - Mesotrophic bog

We ascertained a water level fluctuation in this scarce faunal aquatic biotope, which is also confirmed by the occurrence of the dragonfly Pyrrhosoma nymphula, that occurs in upper parts of old river beds, where the drying up or a water level fluctuation decrease can occur [4]. Regarding the small size of the bog, it can be subjected to periodical drying up, a it has been dependent upon the unsuitable climatic conditions in previous years.

#### Cunovo - Ostrovne lucky - Gravel-ground

This locality was also characterised by a relatively poor species spectrum of dragonflies and aquatic bugs in 1994, due to the small amount of aquatic and shore vegetation.

#### Dunajske Kriviny - Arm

This stationary stand was influenced the most by the Gabcikovo project, because this arm dried up, and with regard to this fact, conditions for the occurrence of aquatic species of animals disapeared there.

#### Bodicka brana - Arm

In this locality in 1993 we found only three species of dragonflies (Platycnemis pennipes, Anax imperator, Libellula quadrimaculata). In 1994 we could already find seven species of dragonflies, including the threatened species Calopteryx splendens, that was found by here Majzlan [9]. That confirms a continual settlement of newly-arisen biotope of a rheophile character (Fig. 1).

#### Kralovska luka - Arm

Quantitatively the richest spectrum of aquatic bugs, with a dominance of Ilyocoris cimicoides, Notonecta glauca, Plea minutissima, Sigaria striata and Gerris rufoscutellatus (Table 2) indicates that this dead arm has been eutrophised. We did not catch any dragonflies in 1993, though in 1994 we observed more rare species of dragonflies: Erythroma viridulum (Coenoagrionidae), Sympecma fusca (Lestidae), Aeschna grandis (Aeschnidae), Cordulia aenea. The species Erythromma viridulum and Platycnemis pennipes occurred in zones not affected by the main channel [4].

#### Istragov - Arm

The continuing trend of drying up in 1994 was manifested by the absence of dragonflies and a small qualitative-quantitative composition of aquatic bugs.

#### Sporna Sihot - Arm

We found the richest species spectrum of dragonflies and aquatic bugs in this locality (Altogether 26 species - Table 1 and 2), which documents the preservation of this biotope. The quantitative rate of rare species was increased, mainly by the rising number of the species Ischnura pumilio (Table 1, Fig. 1) in 1994. We also caught a larva of the rare dragonfly Sympecma fusca and Sympetrum striolatum.

#### Stary les - Arm

We found a quantitatively high representation of aquatic bugs in this locality and in contrast to 1993, where since July we started research here, we found a rich spectrum of dragonflies with an occurrence of the rare species Erythromma viridulum (Coenagrioidae) and Orthetrum albistylum (Corduliidae) in 1994 (Table 1, Fig. 1). This locality, very scarce from a faunal point of view, depends on water level oscillation, which is documented by an occurrence of the dragonfly Pyrrhosoma nymphula, as a subdominant element of the observed coenose.

#### Cicov - Arm

Regarding the higher number of samples in 1994 than in 1993, we found a richer species spectrum of dragonflies and aquatic bugs in 1994 (Altogether 18 species). From the rare species of dragonflies Aeschna grandis (Aeschnidae) occurred here (Table 1), which Majzlan [9] also found here in his previous observations.

#### SUMMARY

From the monitoring results dealing with dragonflies and aquatic bugs we observed the following facts:

1. The localities of Dunajske Kriviny and Istragov are the most influenced by desiccation, which was manifested in the first locality by the total drying of the aquatic biotope and in Istragov by the lowering of the qualitative and quantitative spectrum of dragonflies and aquatic bugs. Therefore we propose to operate the already built, but not functioning water supply in the locality of Istragov, or the raising of water level in the river Danube, for example, by an underwater weir.
2. In 1994 we observed an improvement to the situation through the impact of filling the arm system at Bodiky, in the areas of Bodicka brana and Kralovska luka, with water. This was manifested by the increase in the dragonflies and aquatic bugs species spectrum of the observed groups.
3. Regarding the occurrence of rare dragonflies species we propose to widen the state nature reserve at Lyon through to the monitoring area of Stary les. Also the monitoring areas of Sporna Sihot and Kralovska luka are valuable from the faunal aspect. Also in the state nature reserve of Kopac and Ostrovne lucky the occurrence of rare and threatened species were recorded at present, which confirms the high biological value of this territory.

#### REFERENCES

  [1] Bulankova, E., 1993: The occurrence of some threatened dragonflies species in Slovakia (in Slovak). Spravy Slov. ent. spol. SAV, Bratislava, 4, p. 23-26

  [2] Bulankova, E., Halgos, J.: The Results of monitoring of selected insect groups (Odonata, Culcidae) of stagnant waters in the region of the Gabcikovo project (in Slovak). Proc. of conference: Results and experience from monitoring of biota in the territory influenced by the Gabcikovo project (in press).

  [3] Brtek, J, Rotschein, J,. 1964: Ein Beitrag zur Kenntniss der Hydrofauna und des Reinheitszustandes des tschechoslowakischen Abschnitts der Donau. Biol. prace SAV, 10, p. 1-62.

  [4] Castella, E., 1987: Larval Odonata distribution as a describer of fluvial ecosystem: the Rhone and Ain rivers, France. Adv. Odonatol., 3, p. 23-40.

  [5] David, S., 1991: Dragonflies (Odonata) of basins - the Stiavnicke‚ vrchy mountains, middle Slovakia (in Czech). Prir. Vedy, 10, p. 267-278.

  [6] David, S., 1992: Dragonflies at the surrounding of Mochovce (in Czech). Zbor. Slov. n r. Muz., Prir. Vedy, 38, p. 43-65.

  [7] David, S., 1993: Threatened and rare dragonflies species (Insecta, Odonata) of the Slovak Republic (in Czech). Biológia (Bratislava), 48, p. 177-182.

  [8] David, S., 1994: New findings of rare and threatened dragonflies species (Insecta, Odonata) in the south-west Slovakia (in Czech). Acta mus. Tek., Levice, 2, p. 81-90.

  [9] Majzlan, O., 1992: Significance of some insect groups for the monitoring of the Danubian region (in Slovak). Spravy Slov.ent. spol. SAV, Bratislava, 3, p. 1-9.

  [10] Straka, V., 1989: Dragonflies (Odonata) of the Orava (in Slovak). Stredne Slov., Prir. Vedy, 8, p. 229-236.

  [11] Straka, V., 1990: Dragonflies (Odonata) of Slovakia (in Slovak). Zbor. Slov. nar. Muz., Prir. Vedy, 36, 121-147.

  [12] Trpis, M., 1957: Preliminary survey of dragonflies in the Zitny ostrov island (in Slovak). Biológia (Bratislava), 12, p. 433-447.

Table 1: Dragonflies in the Danubian floodplains

Taxon | Kopac 1 | Kopac 2 | Ostrov. lucky 1 | Ostrov. lucky 2 | Bodiky | Kralovska luka | Istragov | Sporna sihot | Stary les | Cicov
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
ODONATA |  |  |  |  |  |  |  |  |  |
Calopteryx splendens | SR |  |  |  | SD |  |  |  |  |
Sympecma fusca |  |  |  |  | SR | R |  | SR |  |
Lestes sponsa | R |  |  |  |  |  |  | SR |  | SR
Lestes dryas | SR |  |  |  |  |  |  |  |  |
Lestes viridis | SR |  |  |  |  |  |  |  |  |
Lestes virens | SR |  |  |  |  |  |  |  |  |
Platycnemis pennipes | D | D | ED |  | ED |  |  | SR |  |
Pyrrhosoma nymphula |  |  |  | R |  |  |  |  | SD |
Ischnura elegans | SR | SD |  | SD | D | SD |  | SR | SD | R
Ischnura pumilio |  |  |  |  |  |  |  | SD | SR | SD
Ennalagma cyathigerum | R |  |  | D | D | SD |  | R | D | SD
Coenagrion puella | SR | SD |  | R | SD | SR |  | SR | SR | SD
Coenagrion pulchellum |  |  |  | SD | SD | R |  | SR |  | SR
Erythromma najans |  |  | R |  |  | R | SD |  |  | SR
Erythromma viridulum |  |  |  |  |  |  |  |  | SR |
Anax imperator |  |  |  |  | SD | SR |  |  |  | SR
Aeschna grandis |  |  |  |  |  | R |  |  |  | SR
Cordulia aenea |  |  |  |  |  | SD |  |  |  |
Libellula depresa |  |  |  | R |  |  | SD |  | SR |
Libellula quadrimaculata |  |  |  |  | SD |  |  |  |  | SR
Orthetrum cancellatum |  |  |  | SR |  | SR | SD | SR |  |
Orthetrum albistylum |  |  |  |  |  |  |  |  | SR |
Sympetrum meridionale | SR |  |  |  |  |  |  |  |  |
Sympetrum sanquineum | R |  |  |  |  |  |  |  |  |
Sympetrum vulgatum |  |  | ED |  | SD |  |  |  |  |
Sympetrum striolatum |  |  |  |  |  |  |  | SR |  |

Table 2: Aquatic bugs in the danubian floodplains

Taxon | Kopac 1 | Kopac 2 | Ostrov. lucky 1 | Ostrov. lucky 2 | Bodiky | Kralovska luka | Istragov | Sporna sihot | Stary les | Cicov
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
HETEROPTERA |  |  |  |  |  |  |  |  |  |
Micronecta meridionalis |  |  |  |  |  |  |  | R |  |
Cymatia coleoptrata |  |  |  |  |  |  |  | SR |  |
Corixa punctata | R |  |  |  |  |  |  |  |  |
Sigara fossarum |  |  |  | R |  |  | D | R | R |
Sigara striata |  |  |  | SD |  | ED |  | SD | ED | ED
Sigara falleni |  |  |  |  |  | R |  | SD | ED |
Ilyocoris cimicoides | ED | ED | ED | ED |  | ED | D | ED | ED | ED
Notonecta glauca |  |  |  |  |  | ED |  | R | SD | SR
Plea minutissima | ED |  |  | R | SD | ED |  | SD | SD | SD
Hebrus pussiilus |  |  |  |  |  |  |  | SR |  |
Nepa cinerea | SD |  |  | SD |  | SR | SD | SR | SR |
Ranatra linearis |  |  |  |  |  |  |  |  | SR |
Mesovelia furcata |  |  |  |  |  | SR |  |  |  | SD
Hydrometra stagnorum |  |  |  |  |  | SR | ED | SR |  | SR
Hydrometra gracilenta |  |  |  |  | SD | R |  |  |  |
Gerris rufoscutellatus | SR | D |  | R | SD | D | D | R |  | SR
Gerris lacustris |  | D |  | R | SD | R |  | R | SR |
Gerris paludum |  | SD |  | SD | SD | SD |  | SR | SR | R
Gerris argentatus |  |  |  | ED |  | SR |  | SR | SR |
Gerris thoracicus |  |  |  | SD |  | SR |  | R | SR |