Zooplankton in a Danube River Arm Near Rusovce (Slovakia)

Biologia 63/4: 566—573, 2008 Section Zoology DOI: 10.2478/s11756-008-0084-1

Zooplankton in a Danube River Arm near Rusovce (Slovakia)

Marta Illyová1, Katarína Bukvayová2 &DankaNémethová3

1Institute of Zoology, Slovak Academy of Sciences, SK-84506 Bratislava, Slovakia; e-mail: [email protected] 2Department of Ecology, Faculty of Natural Sciences, Comenius University, Mlynská dolina B-2,SK-84215 Bratislava, Slovakia 3Research Centre for Environmental Chemistry and Ecotoxicology, Masaryk University, Kamenice 3,CZ-62500 Brno, Czech Republic

Abstract: Poor quantity of zooplankton was recorded in a Danube arm situated on the right side of the Danube River in Slovakia (river km 1857) in 2002 and 2003. All over the year the arm is significantly influenced by groundwater by reason of seepage. Because of low mean water temperature (12 ◦C) and poorly developed macrovegetation in particular, the arm reminds gravel pit-like. The annual average of zooplankton biomass was low and ranged from 0.35 g m−3 (2002) to 1.28 g m−3 (2003), because of low crustacean abundance. Total cladoceran abundance was excessively low in both years and ranged from 3.5 N L−1 (2002) to 16.6 N L−1(2003). Small species, Bosmina longirostris and Chydorus sphaericus were dominant. Only four adult Copepoda – Cyclops vicinus, Thermocyclops crassus, Eurytemora velox and Eudiaptomus gracilis –were recorded in quantitative samples of both years. In the zooplankton assemblage dominated rotifers (Synchaeta pectinata, Synchaeta oblonga, Polyarthra dolichoptera and Keratella cochlearis) which represented 78% and 67% of total abundance respectively. The total of 19 species of rotifers, 34 Cladocera species and 16 taxa of Copepoda were found. Key words: river-floodplain habitats; Cladocera; Copepoda; Rotifera

Introduction area of Hungary (Gulyás 1987, 1994; Bothár & Ráth 1994 and others). Zooplankton assemblages of the left- The Rusovecké rameno arm, of a plesiopotamal-type bank area in Slovakia were also investigated (e.g., Vra- (Ward et al. 2002), is situated on the right side of novský 1974, 1975, 1985, 1991). Cladocera and Cope- the Danube River (river km 1857) between a flood- poda assemblages in the Danube floodplain area are protection dike and the main river channel, in the up- well-recorded for the long-time monitoring area influ- per part of Žitný ostrov island area near Bratislava city. enced by hydro-electric power plant operations (Vra- Throughout the year, the arm is significantly influenced novský 1997; Illyová & Némethová 2005). by groundwater as a result of two things: groundwater To date, there have not been any zooplankton in- levels and its natural character. Firstly, groundwater vestigations on right-bank Danubian arms in Slovakia, levels increased approximately two meters in this area neither of the ones of the upper part of the river. at the beginning of 1993 after filling-up of the reser- This research examines species composition, seasonal voir Hrušovská zdrž, which is a part of hydro-electric changes in biomass, and abundance of zooplankton as- power plant (Klinda & Lieskovská 1998). Furthermore, semblages of the Rusovecké rameno arm. The objective there are some waterworks on the right side of the main of the study was to obtain new information regarding channel, situated between the Danube, and Rusovce zooplankton quality and quantity in this area, seasonal and Čunovo villages (Rodák & Banský 1995). Secondly, dynamics of the community, and the factors affecting its character, i.e., all-year cold water and poorly devel- the afore mentioned. oped macrovegetation in particular, remains gravel pits or dams (Horecká et al. 1994; Hudec & Hucko 2000). For these reasons, the Rusovecké rameno arm differs from the other Danube arms, which are situated lower Study sites than the Rusovecké and are in the inland delta area. The investigated waterbody is horseshoe-shaped, with a Many zooplankton studies have been conducted in length of 2000 m, width of 100–200 m, and depth of 2–3 m. the Danube River floodplain. Heiler et al. (1994) in- Bottom material consists of alluvial gravel covered by sand. vestigated the arms of the right-bank side of the main Macrovegetation cover is poor; communities consist of Cera- river channel in an Austrian study. Long-term studies tophyllum demersum and Myriophyllum spicatum species. of crustacean assemblages have been conducted on the The branch bank is covered with Typha angustifolia and T. right side arm of this area in the Szigetköz floodplain latifolia.

c 2008 Institute of Zoology, Slovak Academy of Sciences Zooplankton in a Danube River Arm 567

1200

1000

800

600

400 Water stages (cm)

200

0 IV V VI VII VIII IX X IV V VI VII VIII XI X 2002 2003

Fig. 1. The water stages measures at the proﬁle of Bratislava (by SHMU) in 2002 and 2003.

The arm is situated 15 km from Bratislava and is body lengths and from the body length/biomass ratio using named for the nearby village of Rusovce – (GPS coordinates: tables compiled from several bibliographic sources by Mor- 48◦0333 N, 17◦0955 E, 136 m a s. l.) The examined area ducha˘ı-Boltovsko˘ı (1954), Ulomski˘ı (1951, 1961), Nauwerck belongs to the orographic area of the Danubian lowland. (1963), Düssart (1966). Water level in the arm is influenced by seepage water and The Pearson correlation coefficient was used to de- local surface inflow. Connectivity with the Danube occurs termine relationships among water temperature, oxygen, when there is a water level above 400 cm, as measured in chlorophyll-a concentration, and zooplankton density. When Bratislava (Fig. 1), i.e., over 400 cm the arm has flowing necessary variables were logarithmically transformed to nor- water during a flood. The system of waterworks located be- malize the data (e.g., oxygen concentration, and rotifer, tween the Rusovce and Čunovo villages, consists of 23 wells cladoceran and copepod densities). situated at a distance of about 120 m from the seepage canal (Rodák & Banský 1995). At present the groundwater flows from the Danube towards the system of wells and the Water- Results works Rusovce-Ostrovné lúčky-Mokraď, and further inland. The research of zooplankton of the Rusovecké rameno arm Temperature, oxygen was conducted in two hydrologically different years (Fig. 1); In the both years low water temperatures, less than during a great flood in August 2002 (Fig. 1), the side arms ◦ were flushed out and their water levels increased, and in 10 C, were maintained for a long time into the spring 2003 when there was a low water level (less than 400–300 season. Seepage water from the main channel and cm) for almost the whole season. groundwater were the main reasons for these low mean water temperatures in the arm (Table 1). There was no significant increase in temperatures before July of Methods ◦ ◦ either year (15 Cand18C, respectively); the highest ◦ Samples were collected during the growing season, from temperature (20 C) occurred in September (Fig. 2). March to February and December to November, in 2002 and Seasonal presence of oxygen had balanced values 2003. No samples were collected in August 2002 because of during the two years, but the average annual values −1 −1 flooding. Water for physico-chemical analyses, chlorophyll- were not similar: 7.71 mg L (2002) and 9.34 µgL a, and quantitative zooplankton samples were collected from (2003). The highest value (12.48 mg L−1) was recorded the surface layer of open water; samples were integrated in September 2003. This value correlates with the in- from the whole water column. Qualitative zooplankton sam- crease of chlorophyll-a maxima in September. The oxy- ples were collected from open water and littoral vegeta- gen correlated negatively with water temperature (r = tion. In situ water temperature ( ◦C) was recorded and oxy- −1 −0.478, P = 0.038). gen concentration (mg L ) was measured according to the Winkler method. Chlorophyll-a (chl-a) was measured by ISO Standard method (ISO 10260:1992). Phytoplankton Seasonal dynamics of zooplankton density identification and enumeration were not analysed in detail. Qualitative zooplankton samples were obtained using Rotatoria vertical tows from the bottom to top of water column using In both years rotifers dominated abundance values plankton net (60–70 µm mesh size). Quantitative samples (78% and 67%) and the average annual value of rotifer were acquired with a Patalas-type plankton sampler by col- quantity was similar in both years (Table 1). Typical lecting 10 L from a water column. Zooplankton was concen- spring development of rotifers (Devetter 1998) was in- trated using a phosphor-bronze sieve (40–50 µm mesh size) −1 significant in both years. In pelagial areas the species and preserved in formalin. Zooplankton abundance (N L ) was assessed in a 1-ml Sedgewick-Rafter chamber. Occur- Synchaeta pectinata (84%), Polyarthra dolichoptera rence was evaluated on a percentage basis (number of sam- (74%), and Keratella cochlearis (61%) had the highest ples where the species was present). Biomass (g m−3)was occurrences. The density of rotifers correlated signifi- established as wet weight calculated from the mean recorded cantly with water temperature (r = 0.486, P = 0.035) 568 M. Illyová et al.

Table 1. Mean annual values of some physicochemical and biological parameters in Rusovecké rameno arm in the production period of 2002 and 2003.

2002 2003 Unit Maximum water temperature 19.0 ( ◦C) 20.5 ( ◦C)

Mean SD Mean SD

Water temperature ( ◦C) 12.1 4.5 12.8 6.6 Oxygen (mg L−1) 7.7 0.7 9.3 2.0 Chlorophyll-a (µgL−1) 19.6 11.7 21.5 9.2 Rotifera (N L−1) 73.6 44.1 73.4 84.1 Asplanchna priodonta (N L−1) 18.1 21.4 8.2 10.7 Keratella cochlearis (N L−1) 7.2 6.4 10.0 6.9 Polyarthra dolichoptera (N L−1) 10.6 13.4 5.9 7.1 Synchaeta pectinata (N L−1) 25.8 27.4 38.4 46.4 Cladocera density (N L−1) 3.5 3.9 16.6 30.5 Bosmina longirostris (N L−1) 2.7 4.2 2.4 3.4 Chydorus sphaericus (N L−1) 0.4 0.7 10.0 25.7 Copepoda density (N L−1) 16.3 8.3 20.3 13.4

Total density (N L−1) 93.4 50.3 110.2 92.4 Total wet biomass (g m−3) 0.35 0.41 1.28 2.14

Oxygen Temperature

25 14 12

20 ) C) -1 o 10 15 8

10 6 4 Oxygen (mg L

Temperature ( 5 2 0 0 III. IV. V. VI. VII. VIII IX. X. XI. XII. II. III. IV. V. VI. VII. VIII. IX. X. XI. 2002 2003

Fig. 2. Seasonal changes of water temperature and oxygen in Rusovecké rameno arm and the temperature in main channel in 2002 and 2003. and with concentration of chl-a (r = 0.458, P = 0.049). essentially free of Daphnia spp., and other cladocerans Rotifer density was not significantly correlated to oxy- were also rare. During both years, Chydorus sphaericus gen concentration (r = −0.289, P = 0.230). (54%) and Bosmina longirostris (53%) had the highest In 2002, the distribution of rotifer abundance was occurrence. almost identical to the distribution of total zooplankton There was no statistically significant correlation of abundance (Fig. 3). In the first half of a growing sea- cladoceran density with water temperature, chl-a con- son Synchaeta pectinata had the highest density (April, centration, or oxygen concentration (in all cases P > 86 N L−1), in summer Asplanchna priodonta predomi- 0.05). nated (July, 39 N L−1). These big rotifer species were Total Cladocera abundance was excessively low in also dominate from September (A. priodonta,57N both years (Table 1, Fig. 3). In 2002, abundance val- L−1) to October. In 2003, only a moderate increase in ues of individual species varied from > 1NL−1 to abundance of rotifers was recorded in spring. The de- 12.5 N L−1. Most species (Ch. sphaericus and Pleu- crease in abundance that followed in May can be related roxus aduncus), except for B. longirostris (max. 12.5 to the presence of a predator Cyclops vicinus (Devet- NL−1, October), occurred in densities lower than 1 N ter & Seďa 2003). Maximum abundance of rotifers was L−1. The first increase in cladoceran density and max- recorded in summer (July, 315 N L−1). The highest imum of the two seasons (107 N L−1) was recorded density at that time was for S. pectinata (168 N L−1), in May 2003. During that time Ch. sphaericus (87 N which is also the highest individual quantity value of L−1) had the highest abundance. Values of cladoceran rotifers recorded in the two years. abundance were low in the following period; B. longirostris (max. 9.5 N L−1, July) was dominate from Cladocera June to August; filter feeding species, such as Daph- In 2002, cladocerans comprised 4% of total abundance; nia spp. and Diaphanosoma spp., were only found oc- in 2003 they made up 14%. Pelagic zooplankton was casionally in summer samples. In the second half of Zooplankton in a Danube River Arm 569

Rotatoria Copepoda Cladocera Total density 400

300

200

100 Abundance [N.L-1]

0 III. IV. V. VI. VII. VIII IX. X. XI. XII. II. III. IV. V. VI. VII. VIII. IX. X. XI. 2002 2003

Fig. 3. Abundance (N L−1) of zooplankton in the Rusovecké rameno arm during the season in 2002–2003.

Rotatoria Copepoda Cladocera chl-a 2.5 45 7.5 40

2 35

) ) -1 -3 30 L

1.5 (µg 25 ll-a ll-a y

20 h 1 p 15

Zooplankton (g m Zooplankton F Chloro 10 0.5

0 0 III. IV. V. VI. VII. VIII IX. X. XI. XII. II. III. IV. V. VI. VII. VIII. IX. X. XI. 2002 2003

Fig. 4. Development of wet biomass (g m−3) of zooplankton (Rotatoria, Cladocera and Copepoda) with relation to chlorophyll-a (µgL−1) in the Rusovecké rameno arm during the season in 2002–2003.

a growing season (in 2003) the occurrence of phy- Seasonal dynamics of zooplankton biomass and tophilous species (P. aduncus, Simocephalus vetulus, chlorophyll-a and others) was recorded in pelagial; and Sida crys- In 2002, the percentage of individual zooplankton tallina (6 N L−1, September) was of the highest abun- groups in total biomass was: Rotifers 78, Cladocera dance. 20, and Copepoda 2. The mean value of wet zooplankton biomass was 0.35 g m−3, and average concentra- Copepoda tion of chl-a was 19.6 µgL−1 (Table 1). Values of zoo- The proportion of copepods in total abundance of zooplankton biomass were significantly below average in plankton was low in both years: 17% (2002) and 18% spring (> 0.30 g m−3), while the highest chl-a val- (2003). Copepods density did not correlate significantly ues were recorded at that same time (April, 39.07 µg with oxygen (r = −0.018, P = 0.942). However, the L−1) (Fig. 4). However, after the spring increase in the correlation of copepods density and water temperature algal population there was no subsequent, typical in- (r = 0.542, P = 0.017), as well as with chl-a concen- crease in zooplankton biomass, as expected. Zooplank- tration (r = 0.615, P = 0.005) was statistically signifi- ton biomass was poor throughout the whole summer cant. period (Fig. 4). In September 2002, the second increase Developmental nauplia and copepodites were com- of chl-a (31.9 µgL−1) was recorded in conjunction with monly present during both years. Actually, no adult a very low zooplankton biomass (1.38 g m−3). A con- Copepoda were recorded in quantitative samples in siderable portion of the biomass was represented by ro- 2002. In 2003, there were 4 adult species present. Cyc- tifers (0.25 g m−3), with Asplanchna priodonta (92%) lops vicinus (3.5 N L−1) was recorded only in May, predominating. A relatively higher amount of biomass Thermocyclops crassus (1 N L−1) was found in Septem- was maintained in October and November (Fig. 4), ber and the species Eurytemora velox and Eudiapto- when there was a significant increase in Cladocera, par- mus gracilis occurred (0.5 N L−1 both) in October and ticularly of Bosmina longirostris. November. In 2003, the percentage of individual zooplankton 570 M. Illyová et al. groups in total biomass was: Rotifers 20%, Cladocera sented. Thus, there was no decrease in phytoplank- 70%, and Copepoda 10%. Average zooplankton biomass ton as a consequence of herbivore grazing in a sense was1.28gm−3, and average chl-a concentration was of PEG model (Sommer et al. 1986). Poor develop- 21.5 µgL−1. The first significant increase in chl-a values ment of macrovegetation was probably affected by high was recorded in May (27.2 µgL−1), with a maximum groundwater level. Amoros & Bornette (1999) detected increase (35.5 µgL−1) occurring in August. These chl-a that connectivity of the arm and groundwater could values classify the arm as highly eutrophic (Straškraba indirectly affect diversity of water plants, and pres- et al. 1993). There were three peaks of increase in sea- ence or absence of submerged and natant vegetation. sonal dynamics of zooplankton biomass; the first in- The increase in chl-a values in September 2002 could crease in biomass was recorded in May (1.98 g m−3), be related to flooding in August. Heiler et al. (1994) with phytoplankton development peaking at the same stated that the increase in chl-a after flooding is linked time. Planktonic crustaceans Ch. sphaericus (43%) and with the increase in phosphorus concentration. How- C. vicinus (44%) predominated. The second peak of ever, we did not record expected increase of zooplank- zooplankton growth was recorded in July (1.43 g m−3), ton biomass after increasing of phytoplankton biomass. which was affected by rotifers (Synchaeta spp.). Lastly, According to Terek (1990), there should be a significant the maximum of zooplankton biomass was recorded in increase in zooplankton biomass within two weeks of a September (7.5 g m−3), when Sida crystallina (97%) flood receding, and there should be an increase in pro- predominated. portion of planktonic crustaceans as well. This was not the case, and was probably due to low water tempera- Rotatoria, Cladocera and Copepoda tures in the arm as previously mentioned. Nineteen Rotatoria, 34 Cladocera and 16 Copepoda Low water temperature was the major factor af- species were found in 2002–2003 (Appendix 1). fecting zooplankton development in the Rusovecké rameno arm, as was manifested in low abundance and Discussion also low biomass values. Considering all year-round low water temperature and low value of zooplankton Very low average temperatures of water were recorded biomass the Rusovecké arm met the characteristics of (12 ◦C) in both of the years, while summer maxima did gravel-pits (Horecká et al. 1994) or reservoirs (Hudec not exceed 21 ◦C. The high long-term air temperatures & Hucko 2000; Hudcovicová & Vranovský 2000), rather in summer of 2003 did not increase the water tempera- than meeting the biomass values of Danubian arms (Ta- ture in the arm. It is because the arm is enriched with ble 2). All year-round low zooplankton biomass was in groundwater and seepage water. Cold water is rather a gravel-pit Senec, with the maximum of 0.845 g m−3 typical for the Danube and its side arms. However, sum- in October (Horecká et al. 1994). Low biomass val- mer temperatures in the arms are usually higher than ues were also typical for a middle-sized dimictic valley those of the main river channel that can reach 28 ◦C reservoir Dubnik II (1.9 and 1.7 mg L−1), as a conse- (Vranovský 1985). quence of high fish stocking (Hudcovicová & Vranovský Average annual values in chl-a in the arm were 2000). In Zemplínska Šírava reservoir, there were low relatively high and maximum values of chl-a corre- zooplankton biomass values (4.3 mg L−1 and 1.7 mg sponded with high eutrophication (Straškraba et al. L−1) despite biotopic eutrophication (Hudec & Hucko 1993) of a biotope. Considering low water tempera- 2000) (Table 2). ture in the arm one would expect also low biomass of However, neither Danubian arms can be described phytoplankton, resembling that of oligosaprobic gravel as significantly high in zooplankton biomass (Table 2). pits (from 2.1 µgL−1 to 4.8 µgL−1)(Horeckáetal. To data, the average annual biomass in the Žofin arm 1994) or waterworks reservoirs (from 8.80 µgL−1 to 21 ranged from 16 to 8.4 and 7 g m−3 (Vranovský 1975). µgL−1) (Hudec & Hucko 2000). However, the values Similarly, in a plesiopotamal-type arm, near Trstená obtained from the Rusovecké arm corresponded more village, the biomass of the medial zooplankton reached with the values recorded in other Danubian arms. Štef- the average of 10.4 g m−3 (Vranovský 1991) during the ková (1998) recorded chl-a values in the Danube arms warm part of the year. In the two side arms of the of 11.7 µgL−1 to 36.9 µgL−1, depending on their hy- Danube at Baka (1,820.5–1,825.5 river km) the author drologic regime and presence of macrovegetation. Sim- found average biomass values of 6.0 g m−3 and 7.5 g ilar average annual values of chl-a (32.8 µgL−1 or m−3, in the following years the values were lower: 2.0 g 27.8 µgL−1) were recorded by Vranovský (1974) in m−3 a3.0gm−3 (Vranovský 1974, 1985). According to the two side arms of the Danube at Baka (1,820.5– Vranovský (1995), the water temperature and current 1,825.5 river km). Relatively high values of chl-a in the velocity are considered to be the most important factors Rusovecké rameno arm from April to September can influencing the zooplankton biomass in the arm system. be explained by (i) the structure of zooplankton, i.e., We have learned that the open water zone was predomination of rotifer and small cladoceran species, dominated by rotifers, particularly Brachionus spp. In and (ii) minimal macrovegetation in littoral zone. Dur- a similar way, rotifers dominated zooplankton in the ing both years rotifers were dominated plankton abun- arm system on the right bank of the Danube (Aus- dance, while filtrate-feeding crustaceans (genera Daph- tria), in both number of species and their density (80%) nia, Diaphanosoma, Eudiaptomus) were poorly repre- (Heiler et al. 1994). Unlike our results, the species Bra- Zooplankton in a Danube River Arm 571

Table 2. Comparison of mean zooplankton biomass in Danube arms and reservoirs.

Year Mean biomass (g m−3) Reference

Danube Rusovce arm 2002 0.35 this study Danube Rusovce arm 2003 1.28 this study

Danube arms Žofín arm 1971 16 Vranovský (1975) Žofín arm 1972 8.4 Vranovský (1975) Žofín arm 1973 7 Vranovský (1975) Trstená n.Ostrove 1989 10.4 Vranovský (1991) Baka arm 1971 7.5 Vranovský (1974) Baka arm 1972 6 Vranovský (1974) Baka arm A 1976–1977 5.2 Vranovský (1985) Baka arm A 1977–1978 3 Vranovský (1985) Baka arm B 1977–1978 2 Vranovský (1985)

Reservoirs Senec gravel-pit 1989 0.15 Horecká et al. (1994) Senec gravel-pit 1990 0.16 Horecká et al. (1994) Dubník II 1996 1.9 Hudcovicová & Vranovský (2000) Dubník II 1997 1.7 Hudcovicová & Vranovský (2000) Zemlínska Šírava 1998 4.3 Hudec & Hucko (2000) Zemlínska Šírava 1999 1.78 Hudec & Hucko (2000)

chionus calyciflorus, B. angularis, Polyarthra vulgaris, evaluation of species spectrum only from an open wa- and Keratella cochlearis dominated, and these are in- ter zone wherein littoral was not included. These make dicators of eutrophic conditions. Naidenow (1998) also only 27% out of 70 rotifer species recorded in the late reported a high dominance of these species, up to 97%, 1990’s in the Danubian arms (Naidenow 1998). in the main river channel of the Danube and its side arms. Species Polyarthra dolichoptera and Keratella cho- Acknowledgements chlearis predominated, often occurring in mass in spring (Devetter 1998) together with Synchaeta pecti- This study was partially supported by grant No. 1/4353/07 nata. All three dominant rotifer species are typical for from Slovak Grant Agency for Science VEGA. The manu- script preparation was supported by the Ministry of Edu- large Slovakian reservoirs (Hudec 2000). Some differ- cation, Youth and Sports of the Czech Republic (grant No. ences were recorded in biomass peaks (mainly clado- 0021622412). ceran) between the two years. In 2003, there was an increase in biomass of Cladocera. This year was different from the previous one because of a more stabile hydro- References logic regime, development of submerged plants (Cerato- phyllum demersum, Myriophyllum sp.), and planktonic Amoros C. & Bornette G. 1999. Antagonistic and cumulative crustacean increases. effects of connectivity: A predictive model based on aquatic 115: The number of cladoceran (34) and copepod (16) vegetation in riverine wetlands. Arch. Hydrobiol. Suppl. 311–327. species is relatively high and corresponds with other Bothár A. & Ráth B. 1994. Abundance dynamic of crustacean in Danubian arms (Gulyás 1994; Bothár & Ráth 1994; Il- different littoral biotopes of the “Szigetköz” side arm system, lyová & Némethová 2005). The number of cladoceran River Danube, Hungary. Verh. Int. Verein. Limnol. 25: 1684– species found in the Rusovecké rameno arm represents 1687. as much as a half (54%) of all the species recorded in Devetter M. 1998. Influence of environmental factors on the rotifer assemblage in an artificial lake. Hydrobiologia 378/388: a (15 years) long-term monitoring of cladoceran as- 171–178. semblages in the Danube floodplain area (Illyová & Devetter M. & Seďa J. 2003. Společenstvo vířníkú přehradní ná- Némethová 2005). Similarly, the number of copepod drže pod vlivem predace C. vicinus, pp. 87–89. In: Bitušík P. species in the arm is a half of the number of species & Novikmec M. (eds), Acta Facultatis Ecologiae 10, Suppl. 1, Proc. 13th Conference of Slovak Limnol. Soc. & Czech Lim- (30) recorded in monitoring of the Danube river-basin nol. Soc., Banská Štiavnica. waters by Vranovský (1997). Considering the number Düssart B. 1966. Limnologie. L’étude des eaux continentales. of species – according to classification of biotope ori- Guathier-Villars, Paris, 677 pp. gin (Hudec 1999) – the Rusovecké rameno arm can be Gulyás P. 1987. Tägliche Zooplankton-Untersuchungen im Do- classified into an original biotope category. Although nau-Nebenarm bei Ásványráró in Sommer 1985. Arbeitsta- gung der IAD, Passau/Deutchland, Szigetköz. Limnologie rotifer species were the most prevalent zooplankter in Aktuell 2: 63–78. this study, their low numbers in comparison to other Gulyás P. 1994. Studies on Rotatoria and Crustacea in the vari- studies is most likely due to sampling methodology; our ous water-bodies of Szigetköz. Limnologie Aktuell 2: 63–78. 572 M. Illyová et al.

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Received June 12, 2007 Accepted March 5, 2008

Appendix 1. Presence of zooplankton species in the Rusovecké rameno arm in 2002 (1) and 2003 (2).

Month F M A M J J A S O N D

1212121212121212121212 Rotatoria Asplanchna brightwelli Gosse, 1850 + A. priodonta Gosse, 1850 + + + + + + + + + + Bipalpus hudsoni Wierzejski et Zacharias, 1893 + + + Brachionus angularis Gosse, 1851 + + B. calyciflorus Pallas, 1766 +++++ + ++++++++ Colurella uncinata O.F.Müller, 1773 + + + + + + + + + Euchlanis dilatata Ehrenberg, 1832 + + + + + + + Filinia longiseta Ehrenberg, 1834 + + + + + + Keratella cochlearis Gosse, 1851 + +++++++ +++++ + Keratella quadrata (O.F.Müller, 1786) + Lecane luna O.F.Müller, 1776 + + Lepadella triptera Ehrenberg, 1832 + + + Notholca acuminata Ehrenberg, 1832 + + + N. squamula O.F.Müller, 1786 + + + Polyarthra dolichoptera Idelson, 1925 + + + +++++++ ++++++ + Zooplankton in a Danube River Arm 573

Appendix 1. (continued)

Month F M A M J J A S O N D

1212121212121212121212

P. euryptera Wierzejski, 1891 ++ + P. remata Slorikov, 1896 + Synchaeta oblonga Ehrenberg, 1832 + ++++++++++ ++ + ++ S. pectinata Ehrenberg, 1832 + ++++++++++ ++++++++ Cladocera Acroperus harpae (Baird, 1834) + + + + + + + + + + + Alona affinis (Leydig, 1960) + + + + + + + + + A. costata Sars, 1862 + A. guttata Sars, 1862 + A. quadrangularis (O.F.Müller, 1785) + + + A. rectangula Sars, 1862 + Alonella nana (Baird, 1850) + + + + Bosmina coregoni Baird, 1857 + + + B. longirostris (O.F.Müller, 1785) + + + + + + + +++++ Camptocercus rectirostris Schoedler, 1862 + Ceriodaphnia pulchella Sars, 1862 + + + Daphnia ambigua Scourfield, 1948 + D. cucullata Sars, 1862 + + + + D. longispina O.F.Müller, 1785 + D. parvula Fordyce, 1901 + Diaphanosoma mongolianum Ueno, 1939 + D. orghidani Negrea, 1982 + + Disparalona rostrata (Koch, 1841) + + Eurycercus lamellatus O.F.Müller, 1875 + + Chydorus sphaericus (O.F.Müller, 1785) + + ++++++ +++ Ilyocryptus agilis Kurz, 1878 + Leydigia leydigii Schoedler, 1863 + + + Macrothrix laticornis (Jurine, 1820) + Moina micrura Kurz, 1874 + + Pleuroxus aduncus (Jurine, 1820) + + + + + + + + ++++ P. denticulatus Birge, 1875 +++ P. laevis Sars, 1862 ++++ P. truncatus (O.F.Müller, 1785) + + + + + + ++++ P. uncinatus Baird, 1850 + + + + + Polyphemus pediculus (L., 1761) + + + + Scapholeberis mucronata (O.F.Müller, 1785) + + + + + + + Sida crystallina (Koch, 1776) +++++ Simocephalus serrulatus (Koch, 1841) + S. vetulus (O.F.Müller, 1776) + + + + + + + ++++ Copepoda Acanthocyclops robustus (Sars, 1863) + Cyclops strenuus Fischer, 1851 + C. vicinus Uljanin, 1875 + + + + + Diacyclops bicuspidatus (Claus, 1857) + Ectocyclops phaleratus Koch, 1838 + Eucyclops serrulatus (Fischer, 1851) + ++++++ + ++ + E. macruroides (Lilljeborg, 1901) + + E. speratus Lilljeborg, 1901 + Eudiaptomus gracilis (Sars, 1863) + + Eurytemora velox (Lilljeborg, 1853) ++ Macrocyclops albidus (Jurine, 1820) + + + + + M. fuscus (Jurine, 1820) + + Mesocyclops leuckarti (Claus, 1857) + + Nitocra hibernica (Brady, 1880) + + Thermocyclops crassus (Fischer, 1853) + T. oithonoides (Sars, 1863) ++ +