Eudiaptomus graciloides (Lilljeborg, 1888)

Brakovska, Aija, Paidere, Jana & Škute, Artūrs, 2016, Number And Dynamics Of Zooplankton Taxa In The Daugava River And Pļaviņas Reservoir, Acta Biologica Universitatis Daugavpiliensis 16 (1), pp. 15-29 : 23-26

Eudiaptomus graciloides , Cyclops sp. and a dominates in river plankton both qualitatively and large number subadult specimens - Nauplii and quantitatively (Gbemisola 2003, Deksne 2011, Copepodite were identified in Copepoda group. Deksne et al. 2010, Lair 2006, Pace et al. 1992, The highest percentage of Rotifera taxa were Thorp et al. 2006, Thorp & Mantovani 2005,

Synchaeta sp. - 17%, Keratella cochlearis- 28.1%, Pourriot et al. 1997, Шкуте 1973, Шкуте 1976).

Polyarthra vulgaris- 7%, Polyarthra major- 11%, The results of our research show that the greatest

Asplanchna priodonta- 4.9% and Keratella diversity of zooplankton taxa is in Rotifera group quadrata- 15.6%. The highest percentage both in the Daugava River and at the Pļaviņas of Cladocera taxa were Bosmina coregoni- Reservoir. The greatest diversity of zooplankton 0.9%, Chydorus ovalis- 1.5%, Diaphanosoma taxa was also established among Rotifera species brachyurum- 0.9%, Bosmina longispina- 0.3% that were found in the Daugava near Daugavpils and in some places also Daphnia cucullata - 1.2%, (Deksne 2011, Deksne et al. 2010, Шкуте 1973,

Acroperus harpae - 2.6% and Ceriodaphnia Шкуте 1976 ). However, these authors in their quadrangula- 4.6%. When compared the studies mentioned that sometimes during the composition of taxa differences both in July and summer and autumn Cladocera group is also in September, the Rotifera group did not differ widely represented. In our case, taxa of Rotifera substantially e.g. common number of taxa were group were observed at the Pļaviņas Reservoir 16. Cladocera taxa in the samples in September in July, however in September the number of were more diverse, where 5 taxa were similar to taxa rapidly decreased, while many of Cladocera the samples identified in July and 12 taxa were group taxa- Acroperus harpae , Diaphanosoma only found in the samples in September. Water brachyurum un Ceriodaphnia quadrangula taxa temperature in the upper layer of the Pļaviņas appeared in September ( Table 4). However, Reservoir in July 2015 was 21 0 C, the dissolved taking into account that the weight of the majority oxygen content was 12 mg /l and chlorophyll α of Cladocera and Copepoda representatives concentration was 5 μg/l. On the other hand, exceeds the weight of representatives of Rotifera water temperature in the upper layer in September group, it can be concluded in terms of biomass 2015 was 19 0 C, the dissolved oxygen content that all zooplankton groups in the Daugava are was 6 mg /l and chlorophyll α concentration was equally well represented. It should be noted 1.3 μg/l. that throughout all the stages of rivers and reservoir under research, the variation among Big zooplankton biodiversity in the

Daugava River and in the Pļaviņas

Reservoir is due to the Daugava large catchment area - 87,900 km 2

(Kavacs 1994), which includes tributaries and the water system.

When water level in the river changes the exchange of plankton fauna takes place between these water bodies. In the 60-ies of

20 th century, Škute (1971) carried out a research of 28 Daugava

River tributaries and noted that the upper reaches of the Daugava

River tributaries have a significant effect on the Daugava zooplankton cenosis, zooplankton quantity even doubled in some of the tributaries Fig. 2. Zooplankton groups distribution in water bodies pelagic, of the river. Rotifera usually littoral / gulf area.

zooplankton quantity is similar, but the right bank quantitative and qualitative parameters of taxa are and the left bank are different. Such variation compared (by Shannon-Wiener diversity) both in is also determined by the influence of water the Daugava before the Pļaviņas Reservoir, at the body hydrological, hidrometreological factors, place where the Aiviekste River flows into the where the thermal water regime and water level Daugava and in the Pļaviņas Reservoir ( Fig. 4 ), it fluctuations are of particular importance, as is evident that the greater diversity of taxa can be well as overgrowth of the water body and the observed directly in the river. By contrast, there pollution degree. When compared prevalence of is no such a big diversity of taxa in the reservoir, zooplankton groups in pelagic and littoral area, but the dominance of certain taxa appears there, the largest number of species can be observed in which is not typical of the river plankton. The littoral and bays of reservoir (Fig. 2), in particular number of the species does not only depend on it could be observed in the samples which where the sampling time, habitat diversity, but also on collected in July. It could be explained that the the sampling frequency during the season and stream is slower here, as well as the vegetation on the size of the water body (ЛаЗарева 2010). is richer, which is a very important factor for the Several authors in their researches (Czerniawski development of certain zooplankton. & Domagała 2010 a, b, Chang et al. 2008, Lair 2006, Крылов 2005) noted the influence of fish In particular, there are far more organisms on the on zooplankton cenosis, but the influence of left bank (Table 5, 6), which can be explained fish is significant only in small rivers. The main by the fact that the left bank was generally more overgrown with macrophytes. Zooplankton taxa in all groups, i.e. Rotifera,

Cladocera and Copepoda, were found in macrophytes, compared to the pelagic and littoral waters without macrophytes (Fig. 3),

while in the middle of the rivers and the reservoirs, where there was a faster flow and there was no macrophyte diversity, their number significantly decreased.

The sections of the river where there are a lot of macrophyte in the coastal zone, macrophytes become the decisive factor for the formation of the river zooplankton

Fig. 3. Zooplankton groups distribution in different habitats. (Lair 2006, Viroux 2002). When

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identified both in the Daugava River and in the Pļaviņas Reservoir. The identified differences could be due to the fact that zooplankton species are very sensitive to various changes in environmental factors, such as weather conditions, change in each specific place vegetation, overgrow, depth and physico-chemical parameters of the properties as well as with biological characteristics of each species, such as seasonality.

Figures

Fig. 4. Species abundance after Shannon-Wiener index. Research was supported by the national research programme “The influencing factors in large rivers that determine value and dynamic of Latvia’s ecosystems under the number of zooplankton, in particular changing climate – EVIDEnT” Sub-project 4.6. crustaceans, is the river hydrology and predators Freshwater ecosystem services and biological (Baranyi et al. 2002, Basu & Pick 1996, Chang diversity. et al. 2001, Lair 2006, Saunders & Lewis 1988, Thorp & Casper 2003, Thorp & Mantovani 2005, Viroux 2002). REFERENCES