The aim of this study was to determine microcrustacean secondary production (P/B) and a herbivory ratio (ZB:PB) in the River Danube and a floodplain lake to reveal models in plankton food web ...functioning. P/B was used to assess population variation under different environmental conditions, while ZB:PB provided information on the zooplankton grazing intensity on algae. Seasonal changes, displayed by the hydrological regime, i.e., related water level fluctuation, were expected to explain different plankton patterns between the study sites as a result of unlike community composition and food quality. The structural equation modelling we used identified specific pathways of measured indexes at the individual localities. Although the direct impact of water level fluctuation on the studied communities was low, the following difference in abiotic components might have caused shifts in zooplankton assemblages that changed P/B and ZB:PB ratios. In the floodplain lake, P/B was primarily influenced by biotic components, and herbivory alteration was expressed through top-down control. On the contrary, P/B in the riverine system was controlled by an environmental element and herbivory was driven by the bottom-up resources. The results show the usefulness of the studied indexes in determining variations of zooplankton functional processes in the hydrologically dynamic environments.
Rotifers display r‐strategy life‐histories and are adaptable to environmental disturbances. Although rotifers constitute a large proportion of zooplankton in river‐floodplain systems, the influence ...of hydrology on their assemblage has been poorly studied. We postulated that rotifer assemblage and grazing activities were controlled by mechanisms associated with hydrological conditions. We conducted a 5‐year study (Kopački Rit Nature Park, NE Croatia) to assess the influence of hydrology on (a) rotifer assemblage during different hydrological phases, (b) the vertical distribution of rotifer abundance, functional feeding guilds, and grazing intensity, and (c) the main drivers affecting rotifer assemblage in the floodplain lake. The results indicated that (a) during isolation, longer residence time and high phytoplankton biomass microfilter‐feeders (mIff) and macrofilter‐feeders (mAff) grazing rates were similar whereas predators (Pr) were the most efficient consumers, (b) during high flow pulses, high conductivity and variable water level governed rotifer grazing rates of mIff and mAff at a retion of 1:2 and a decline of Pr grazing activity, and (c) during the flood pulse, reduced phytoplankton biomasss still resulted in mAff and Pr domination of the community whereas mIff grazing activity remained at the same level. Under stable hydrological conditions algivorous species codominated with bacterivores and predators, suggesting an increased biodiversity and food web interactions. In contrast, throughout the inundation period, algivorous species predominated. However, differences in rotifer assemblage between normal flow and flood pulses indicated the importance of hydrology in shaping rotifer trophic structure through modifying lower trophic levels and the availability of food sources.
Dissimilar life features of Rotifera, Cladocera and Copepoda enable these organisms to respond differently to changes in the hydrological regime which influence alterations in environmental ...characteristics. We investigated the effect of habitat heterogeneity (e.g. eupotamal, parapotamal, palaeopotamal) on individual zooplankton group assemblages and biodiversity indices (α, β and γ diversity) during hydro regime change in floodplain waterbodies. Dissolved oxygen and organic nitrogen concentrations changed significantly among hydrological states while water depth was affected by both site and hydro regime replacement. Each studied site supported different zooplankton assemblage that highly depended on species-specific responses to hydro regime change. Also, individual zooplankton groups exhibited different correlations with specific environmental parameters regarding site change. Throughout the study, rotifers′ local (α) and among-community (β) diversities were susceptible to the site and inundation change while the microcrustacean biodiversity pattern diverged. Copepods highly discriminated different habitat types and hydrological phases at the regional scale (γ diversity), while we found a complete lack of biodiversity dependence on both site and hydrology for Cladocera. Our results show that heterogeneous environments support the development of different zooplankton assemblages that express the within-group dissimilarities. They also point to the importance of identifying processes in hydrologically variable ecosystems that influence biodiversity patterns at an individual zooplankton group level. Our results suggest the use of appropriate zooplankton groups as biological markers in natural habitats and stress the importance of proper management in preserving biodiversity in floodplain areas.
Lake Jošava (Croatia) is a shallow reservoir surrounded by agricultural land. In the present study, the trophic cascade was tested by examining the effects of stocking with common carp on plankton ...and periphytic microphytes. Before stocking, the phytoplankton community was dominated by the chrysophyte
Synura uvella
. In the epilithon and epiphyton, the predominant diatoms were prostrate, stalk-forming, and motile taxa representing an important food source for adult copepods. After stocking, phytoplankton biomass declined and the community shifted towards small centric diatoms, allowing the small-bodied zooplankton to exploit them. The lower biomass of adult copepods allowed rotifers to proliferate and exploit phytoplankton, while small cladocerans and nauplii fed primarily on epilithon. One month after stocking, phytoplankton was dominated by cryptophytes, small centric diatoms and chlorophytes, which were an important food for rotifers, while none of the zooplankton groups showed a significant relationship with the epilithic and epiphytic communities. By the end of the experiment, food was scarce due to reduced biomass of autotrophs, and zooplankton possibly began to feed on other sources. Our results add to the knowledge about the trophic cascade hypothesis in small shallow reservoirs.
To study the early colonization processes, polyethylene terephthalate (PET) microfragments were immersed in Lake Sakadaš and the Drava River and sampled weekly together with the surrounding biotic ...communities - phytoplankton, zooplankton, epixylon in the lake and epilithon in the river. At the end of the study, a rise in water level occurred in the river, which altered the environmental conditions and plankton communities. In studied environments, all of the sampled biotic communities were diverse and abundant. Plastispheres formed in both waters by the seventh day of incubation and developed rapidly, reaching a peak in abundance on the last day of the study. Initial colonization was supported equally by planktonic and periphytic taxa in both environments, but after initial settlement, plastisphere assemblages were affected differently in the river and lake. This study suggests that PET microfragments are a suitable substrate for microphyte settlement and may provide an important pathway for their transport in dynamic freshwater floodplains and river systems.
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•The PET fragments support the rapid development of three-dimensional plastispheres.•Initial colonization is supported by planktonic and periphytic taxa equally.•Following succession, the plastispheres in the lake resemble an epixylic community.•Progression of plastispheres in the river favours the settlement of planktonic taxa.
Changes in the functional groups of zooplankton were studied in autumn in a temperate floodplain lake (Lake Sakadaš, Kopački Rit Nature Park, Croatia) and in the Drava River (in the Croatian part of ...the river). Various abiotic parameters as well as available food sources (phytoplankton and microphytes (algae and cyanobacteria) developing on epixylon, epilithon and artificially introduced microplastics called “plastisphere”) were also studied. The lake was hydrologically isolated from the main river during the study, while the water level of the Drava River fluctuated, resulting in larger variations in limnological parameters. Due to stable conditions in the lake, zooplankton abundance, biomass, and species richness were higher than in the Drava River. In both environments, zooplankton species feeding on bacteria, detrital suspensions, and small algae were most abundant, with predators and microfilter-feeders being more abundant in the lake. Microphytes were diverse and mostly small and medium-sized in phytoplankton and all substrate types. Stable lake conditions promoted higher abundance of the zooplankton group, which effectively uses larger algae as a food source. The lower abundance of zooplankton feeding on larger algae and predatory species in the river suggests that the epilithon and plastisphere community was a less mature community compared to the lake, and the heterotrophic component with ciliates and/or other small heterotrophs was not well developed. The importance of plastispheres was particularly evident under the turbid hydrologic conditions that prevailed in the river at the end of the study, when phytoplankton biomass decreased and zooplankton abundance steadily increased, suggesting that microphytes colonised on microplastics were an additional food source for higher trophic levels.
This paper presents the results of the research on the overall distribution of selenium (Se) in various aquatic compartments (water, sediment, plankton and macrophytes) at six selected sites of the ...Croatian part of the Drava and Danube rivers, the connected floodplain lake and the melioration channel system carried out in two sampling periods (flooding in June and the drought period in September). In addition, the physicochemical water properties, plankton composition and biomass were analysed. Our study revealed low mean Se contents in sediments and water, indicating Se deficiency in the studied freshwater systems. The physicochemical environment, including Se distribution, was primarily influenced by hydrology rather than site-specific biogeochemical and morphological characteristics. The flooding period was characterised by higher Se content in water and higher transparency, nitrate and total nitrogen concentrations than drought conditions. At the river sites, sediment Se content was the highest during the flood period, while at all other sites, higher concentrations were found during the drought, reaching the maximum in the lake. Although Se concentrations were below the threshold for aquatic ecotoxicity, they increased in the following order: water (0.021–0.187 μg Se L−1) < sediments (0.005–0.352 mg Se kg−1) < macrophytes (0.010–0.413 mg Se kg−1) < plankton (0.044–0.518 mg Se kg−1) indicating its possible biomagnification at the bottom of the food chain. Species known for high Se accumulation potential dominated the biomass of the main plankton groups and the composition of the macrophyte community, which may provide a more sensitive and accurate steady-state compartment monitor for Se assessment in freshwater biotopes.
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•Low Se content in sediments and water indicates Se deficiency in the studied area.•Se concentration increased in the order: water < sediments < macrophytes < plankton.•Hydrology influences the Se distribution in aquatic compartments.•Se potentially accumulates at the bottom of the food web.
Istraživački pristup u prirodoslovnim predmetima omogućuje razvoj istraživačkih vještina učenika, potiče njihovu želju za učenjem, ali i pobuđuje interes za znanost. Učenici samostalno pristupaju ...rješavanju problema i stvaraju nove ideje i rješenja. Aktivno sudjeluju u svim istraživačkim procesima od postavljanja ciljeva rada, formuliranja istraživačkog pitanja, prikupljanja rezultata i izvođenja zaključaka. Ovakav način učenja, često u obliku izvanučioničke nastave, pridonosi i lakšem usvajanju nastavnog sadržaja i složenih tematskih cjelina te učenik upoznaje prirodni okoliš, razvija ekološku svijest i vježba snalaženje u prirodi. Primjenom aktivnog poučavanja nastavniku je olakšana korelacija nastavnog sadržaja Biologije sa sadržajem ostalih prirodoslovnih predmeta što pridonosi boljem razumijevanju naučenog. U ovom radu predloženo je istraživanje anatomije, morfologije i ekologije virnjaka s naglaskom na njihovu sposobnost regeneracije kako bi učenici shvatili proces regeneracije oštećenih dijelova tijela kao i uporabu virnjaka kao modela u različitim istraživanjima. Sadržaj ovog rada poslužit će nastavnicima osnovnih i srednjih škola. Samostalnim iskustvenim i istraživačkim učenjem, primjenom metoda suradničkog učenja ili odabirom projektnog učenja, na kreativan se način mogu ostvariti ishodi unutar makrokoncepta prirodoznanstveni pristup u integraciji s ostalim ishodima učenja.
