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Change in metazooplankton abundance in response to flood dynamics and trophic relations in Danubian floodplain lake (Kopački Rit, Croatia)

Palijan G., Galir A.

Polish Journal of Ecology

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2012

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Vol. 60, nr 4

777--787

EN

This study investigated relationships of hydrological variability and potential food resources for metazooplankton groups: rotifers, cladocerans, copepods and nauplii. Samples were collected monthly during ice-free season from March until November in 2006. Two sampling stations were chosen, the one located in Lake Sakadaš, as a segment of Kopački Rit floodplain (Croatia), and the other in the River Danube. Due to hydrological conditions we divided our samples into two hydrological groups which corresponded to: 1/ increased water level i.e. disturbed phase and 2/ decreased water level representing a more stable phase. Abundance of metazooplankton was not significantly different between hydrological groups in the River Danube. However, it was significantly different between hydrological groups in Lake Sakadaš (one-way ANOSIM R = 0.688, P = 0.024), where during a decreased water level higher abundance of metazooplankton was recorded. Rotifers were the most abundant metazooplankton group during the whole investigated period at both stations and between both hydrological groups comprising almost 99% of total metazooplankton abundance. Rotifers were significantly positively correlated with the total number of bacteria, as well as with ammonium and total phosphorous concentrations. The metazooplankton community in Lake Sakadas was negatively influenced by flooding, but not in the River Danube. Compared to the River Danube the investigated floodplain lake showed potential as a storage zone for metazooplankton development during more stable hydrological periods. During that time abundance of rotifers was related to the heterotrophic component of microbial food web. Hence, this investigation adds to the understanding of the metazooplankton dynamics in river-floodplain systems as well as of their relations with trophic levels under variable hydrological conditions.

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Relationship between nematode community and biomass and composition of periphyton developing on artificial substrates in floodplain lake

Vidakovic J., Palijan G., Cerba D.

Polish Journal of Ecology

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2011

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Vol. 59, nr 3

577-588

EN

Periphyton colonisation on artificial substrate (microscopic glass slides) was investigated from July to November 2007, in Lake Sakadas (Danube River floodplain Kopacki rit, Croatia). Two different stations were chosen due to different post - flood conditions. The aim of the study was to follow temporal changes of nematode community composition and trophic structure in relation to periphyton biomass and bacterial abundance. In bryozoan - dominated periphyton (Plumatella emarginata Allman, 1844) nematodes were represented by 86 and 87% of total associated invertebrate fauna at S1 and S2 respectively. Total nematode abundance (up to 600 ind. 10 cm[^-2] at one station and up to 1130 ind. 10 cm[^-2] at another station) correlated significantly with the abundance (meaured as CFUs - colony forming units) of copiotrophic and oligotrophic bacteria at one station (r = 0.963, 0.998, P <0.05) and with organic and inorganic content of periphyton at another station (r = 0.891, 0.899, P <0.05). Nematode trophic groups (epistrate feeders, chewers, detritus feeders and suction feeders) were equally developed at both stations except detritus feeders whose species richness and abundance were significantly higher at the S1. Epistrate feeders were the most abundant trophic group in nematode assemblages at both stations with Chromadorina bioculata being the dominant species. Change in dominance of epistrate feeders by chewers (Brevitobrilus stefanskii) and suction feeders (Crocodorylaimus sp.) coincided with the occurrence of flood pulse. Effect of flood pulse on nematode community structure was probably indirect, alterating concentration of dissolved oxygen which chromadorids are sensitive to. The structure of nematode community developed through time differs between investigated stations indicating high sensitivity to bacterial abundance, periphyton biomass and P. emarginata mats which made the habitat more diverse and patchy.

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Different impact of flood dynamics on the development of culturable planktonic and biofilm bacteria in floodplain lake

Palijan G.

Polish Journal of Ecology

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2010

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Vol. 58, nr 3

439-448

EN

Floodplains are lateral river extensions in which lotic, semi-lotic and lentic habitats are formed resulting in high habitat heterogeniety. Consequently biota development is highely influenced by its location within the floodplain and by the hydrological cycle. In the present paper the development of planktonic and biofilm bacteria associated with artificial substrates were investigated in the floodplain lake of the Danube River (Lake Sakadas, Croatia) during different hydrological situations. The aim of the study was to investigate if there was any difference in the bacterial development between two compartments - plankton and biofilm, and how the floods influence these communities. The samples were taken monthly (July.November 2007) from surface and bottom water layer (plankton) and exposed glass slides (biofilm) at two sampling stations. For these purposes bacterial abundance was estimated by the determination of number of colony forming units (CFUs). The development of bacterioplankton was equal between the sites and had its maximum at the time of falling water after the flood pulse. Bacterioplankton abundance correlated significantly with water properties, and it had predictable dynamics comparable with the previous results established in the same floodplain area (Kopacki Rit). The development of biofilm bacteria differed between the sites, and had its maximum prior to the flood pulse, or during the flood. The abundance of attached bacteria correlated with biofilm biomass while it was not significantly correlated with the water properties. Such results describe different development of planktonic and biofilm bacteria. Biofilm bacteria are more independent, compared to bacterioplankton, from the floodplain hydrology.