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 Szigetk¨oz 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), D¨ussart (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.