Effects of emergent vegetation on zooplankton and epiphyton communities in oxbow lakes of river Krapina

U istraživanju zooplanktona i epifitona, provedenog tijekom ljetnog razdoblja 2008. godine u dva rukavca rijeke Krapine, bile su obuhvaćene skupine kolnjaka (Rotifera), veslonožaca (Copepoda) i rašljoticalaca (Cladocera). Uzorci zooplanktona su uzimani u svakom jezeru u zoni slobodne vode i litorala. Epifiton je strugan s makrofita (Iris pseudacorus i Mentha aquatica) uzetih na postajama litorala. Osnovne hipoteze ovog rada bile su: (i) širina litoralne zone i prozirnost vode utječu na horizontalnu raspodjelu zooplanktona u plitkim jezerima; (ii) širina zone makrofita te struktura stabljike utječu na sastav epifitona. Ciljevi istraživanja bili su: 1) analizirati razlike kvalitativnog i kvantitativnog sastava zooplanktona slobodne vode i litorala u rukavcima s različitom prozirnošću vode; 2) analizirati utjecaj abiotičkih i biotičkih čimbenika na sastav zooplanktona u zoni slobodne vode i u litoralnoj zoni; 3) utvrditi utjecaj abiotičkih i biotičkih čimbenika na kvalitativni i kvantitativni sastav epifitona. Fizičko-kemijski čimbenici te izvori hrane nisu se značajno razlikovali unutar rukavaca. Između rukavaca zabilježena je značajna razlika u prozirnosti vode i koncentraciji klorofila a koja je utjecala na sastav zajednica. Manja prozirnost vode u RK1 uvjetovana je užom zonom makrofita i većom koncentracijom suspendiranih organskih tvari, dok je veća prozirnost u RK2 uvjetovana širom zonom makrofita i sastavom zooplanktona. U sastavu zooplanktona obaju rukavaca dominirale su od Rotifera vrste roda Polyarthra te vrsta Keratella cohlearis, od Copepoda ličinački stadiji. Cladocera su u RK1 bili zastupljeni manjim, a u RK2 većim vrstama. Algivorni Rotifera i Copepoda dominirali su u slobodnoj vodi, za što je bila ključna raspoloživost hrane. Predacijski pritisak riba (vizualnih predatora) bio je ublažen manjom prozirnošću vode i višim stupnjem trofije u RK1. Brojnost vrste Bosmina longirostris u slobodnoj zoni određena je kompeticijom s vrstom K. cochlearis i prozirnošću vode, odnosno, predacijskim pritiskom riba, što je pogotovo vidljivo u rukavcu s većom prozirnošću vode i izraženijim predacijskim pritiskom riba - RK2. Veća prozirnost ukazuje na niži stupanj trofije RK2 u odnosu na RK1, što se očitovalo i u manjoj brojnosti zooplanktona. U jezeru sa širom zonom makrofita brojnost svojti epifitona bila je veća. Također, veća brojnost epifitona zabilježena je na strukturno složenijim stabljikama vodene metvice u odnosu na jednostavne stabljike irisa. Raznolikost vrsta makrofita i šira zona makrofita pozitivno utječu na raznolikost i brojnost epifitona.The research of zooplankton and epiphyton was conducted in the summer of 2008 in two oxbow lakes of the river Krapina. The investigation included rotifers (Rotifera), cladocerans (Cladocera) and copepods (Copepoda). Zooplankton samples were collected in free-water zone and littoral of each lake. Epiphyton samples were scraped from plants surfaces (Iris pseudacorus and Mentha aquatica) taken at the littoral stations. The following hypotheses were set: (i) width of littoral zone and water clarity affect horizontal distribution of zooplankton in shallow lakes; (ii) width of macrophyte bed and plant stem structure affect epiphyton composition. The research goals were: 1) to analyse qualitative and quantitative differences of zooplankton composition both in free-water and in littoral zone of lakes with different water clarity; 2) to analyse effects of environmental and biotic factors on both free-water and littoral zooplankton composition; 3) to determine effects of environmental and biotic factors on both the qualitative and quantitative epiphyton composition. Environmental factors and food resources did not differ significantly within the lakes. However, between the lakes the significant difference in water clarity and chlorophyl a was determined. RK1 smaller water clarity was induced by a narrower macrophyte bed and a greater concentration of suspended organic matter, while RK2 greater water clarity was induced by a wider macrophyte bed zooplankton composition. In zooplankton composition of both lakes dominant Rotifera were species of genus Polyarthra and species Keratella cochlearis and Copepoda larval stages. Cladocera were represented with smaller species in RK1, while in RK2 larger species were found. Algivoric Rotofera and Copepoda were dominant in free-water zones because of food availability. Fish predatory pressure was reduced by smaller water clarity and higher trophy state in RK1. Abundance of Bosmina longirostris in free-water was determined by food competition with K. Cochlearis and by water clarity, i.e. fish predation which was particurlary visible in RK2 due to a greater water clarity. The higher water clarity indicates lesser trophy level of RK2 in relation to RK1, which was manifested in a smaller zooplankton abundancy. The lake with the wider macrophyte bed had a greater number of epiphyton species. The greater epiphyton abundancy was detected on the morphologicaly more complex stems of Mentha aquatica compared to the simpler ones of Iris pseudacorus. Plant species diversity and wider macrophyte bed intensly affect epiphyton diversity and abundance

Effects of emergent vegetation on zooplankton and epiphyton communities in oxbow lakes of river Krapina

U istraživanju zooplanktona i epifitona, provedenog tijekom ljetnog razdoblja 2008. godine u dva rukavca rijeke Krapine, bile su obuhvaćene skupine kolnjaka (Rotifera), veslonožaca (Copepoda) i rašljoticalaca (Cladocera). Uzorci zooplanktona su uzimani u svakom jezeru u zoni slobodne vode i litorala. Epifiton je strugan s makrofita (Iris pseudacorus i Mentha aquatica) uzetih na postajama litorala. Osnovne hipoteze ovog rada bile su: (i) širina litoralne zone i prozirnost vode utječu na horizontalnu raspodjelu zooplanktona u plitkim jezerima; (ii) širina zone makrofita te struktura stabljike utječu na sastav epifitona. Ciljevi istraživanja bili su: 1) analizirati razlike kvalitativnog i kvantitativnog sastava zooplanktona slobodne vode i litorala u rukavcima s različitom prozirnošću vode; 2) analizirati utjecaj abiotičkih i biotičkih čimbenika na sastav zooplanktona u zoni slobodne vode i u litoralnoj zoni; 3) utvrditi utjecaj abiotičkih i biotičkih čimbenika na kvalitativni i kvantitativni sastav epifitona. Fizičko-kemijski čimbenici te izvori hrane nisu se značajno razlikovali unutar rukavaca. Između rukavaca zabilježena je značajna razlika u prozirnosti vode i koncentraciji klorofila a koja je utjecala na sastav zajednica. Manja prozirnost vode u RK1 uvjetovana je užom zonom makrofita i većom koncentracijom suspendiranih organskih tvari, dok je veća prozirnost u RK2 uvjetovana širom zonom makrofita i sastavom zooplanktona. U sastavu zooplanktona obaju rukavaca dominirale su od Rotifera vrste roda Polyarthra te vrsta Keratella cohlearis, od Copepoda ličinački stadiji. Cladocera su u RK1 bili zastupljeni manjim, a u RK2 većim vrstama. Algivorni Rotifera i Copepoda dominirali su u slobodnoj vodi, za što je bila ključna raspoloživost hrane. Predacijski pritisak riba (vizualnih predatora) bio je ublažen manjom prozirnošću vode i višim stupnjem trofije u RK1. Brojnost vrste Bosmina longirostris u slobodnoj zoni određena je kompeticijom s vrstom K. cochlearis i prozirnošću vode, odnosno, predacijskim pritiskom riba, što je pogotovo vidljivo u rukavcu s većom prozirnošću vode i izraženijim predacijskim pritiskom riba - RK2. Veća prozirnost ukazuje na niži stupanj trofije RK2 u odnosu na RK1, što se očitovalo i u manjoj brojnosti zooplanktona. U jezeru sa širom zonom makrofita brojnost svojti epifitona bila je veća. Također, veća brojnost epifitona zabilježena je na strukturno složenijim stabljikama vodene metvice u odnosu na jednostavne stabljike irisa. Raznolikost vrsta makrofita i šira zona makrofita pozitivno utječu na raznolikost i brojnost epifitona.The research of zooplankton and epiphyton was conducted in the summer of 2008 in two oxbow lakes of the river Krapina. The investigation included rotifers (Rotifera), cladocerans (Cladocera) and copepods (Copepoda). Zooplankton samples were collected in free-water zone and littoral of each lake. Epiphyton samples were scraped from plants surfaces (Iris pseudacorus and Mentha aquatica) taken at the littoral stations. The following hypotheses were set: (i) width of littoral zone and water clarity affect horizontal distribution of zooplankton in shallow lakes; (ii) width of macrophyte bed and plant stem structure affect epiphyton composition. The research goals were: 1) to analyse qualitative and quantitative differences of zooplankton composition both in free-water and in littoral zone of lakes with different water clarity; 2) to analyse effects of environmental and biotic factors on both free-water and littoral zooplankton composition; 3) to determine effects of environmental and biotic factors on both the qualitative and quantitative epiphyton composition. Environmental factors and food resources did not differ significantly within the lakes. However, between the lakes the significant difference in water clarity and chlorophyl a was determined. RK1 smaller water clarity was induced by a narrower macrophyte bed and a greater concentration of suspended organic matter, while RK2 greater water clarity was induced by a wider macrophyte bed zooplankton composition. In zooplankton composition of both lakes dominant Rotifera were species of genus Polyarthra and species Keratella cochlearis and Copepoda larval stages. Cladocera were represented with smaller species in RK1, while in RK2 larger species were found. Algivoric Rotofera and Copepoda were dominant in free-water zones because of food availability. Fish predatory pressure was reduced by smaller water clarity and higher trophy state in RK1. Abundance of Bosmina longirostris in free-water was determined by food competition with K. Cochlearis and by water clarity, i.e. fish predation which was particurlary visible in RK2 due to a greater water clarity. The higher water clarity indicates lesser trophy level of RK2 in relation to RK1, which was manifested in a smaller zooplankton abundancy. The lake with the wider macrophyte bed had a greater number of epiphyton species. The greater epiphyton abundancy was detected on the morphologicaly more complex stems of Mentha aquatica compared to the simpler ones of Iris pseudacorus. Plant species diversity and wider macrophyte bed intensly affect epiphyton diversity and abundance

STRUKTURA ZOOPLANKTONA U MEĐUSOBNO POVEZANIM PLITKIM JEZERIMA

The research of zooplankton diversity, abundance and trophic structure was conducted during the summer period in pelagial zone on the longitudinal profile of the Sutla River Backwater. Investigated site consists of two interconnected basins: transparent Upper Basin with submerged macrophytes and turbid Lower Basin without macrophytes in the littoral zone. In the Upper Basin, abundance and diversity of zooplankton in the pelagial was higher in comparison to the Lower Basin, with prevailing species of genus Keratella as microfilter-feeder, and genera of Polyartha and Trihocerca as macrofilterfeeder rotifers. On the contrary, in the Lower Basin, crustaceans dominated in abundance. Microfilter-feeder cladoceran (Bosmina longirostris) and larval and adult stages of macrofilter-feeder copepod (Macrocyclops albidus) prevailed in the Lower Basin. Fish predation pressure was more pronounced in the pelagial of the Upper Basin, indicated by low cladoceran abundance in the surface layer. Although the studied basins were interconnected, results indicate significant (Mann-Whitney U test, p < 0.05) differences in the zooplankton structure as a potential result of the macrophyte impact on environmental conditions and fish predation pressure.Istraživanje raznolikosti, abundancije i trofičke strukture zooplanktona provedeno je tijekom vegetacijskog razdoblja na pelagičkim postajama longitudinalnog profila rukavca rijeke Sutle koji se sastoji od dva međusobno povezana bazena. Gornji bazen veće je prozirnosti i sa submerznim sastojinama makrofita, Donji bazen veće je mutnoće i bez makrofita. U Gornjem bazenu, brojnost i raznolikost zooplanktona u pelagijalu je bila veća u odnosu na Donji bazen, a prevladavali su kolnjaci, detritivorni-mikrofiltratori roda Keratella i algivorni-makrofiltratori rodova Polyartha i Trihocerca. U Donjem bazenu brojnost planktonskih rakova bila je veća u odnosu na Gornji bazen, a prevladavali su mikrofiltratorski rašljoticalci (Bosmina longirostris) te makrofiltratorski ličinački i adultni stadiji veslonožaca (Macrocyclops albidus). Predacijski pritisak riba bio je izraženiji u pelagijalu Gornjeg bazena, na što ukazuje manja brojnost Cladocera u površinskom sloju. Iako su istraživani bazeni međusobno povezani, rezultati rada ukazuju na značajne razlike (Mann-Whitney U test, p < 0.05) u strukturi zooplanktona kao rezultat utjecaja makrofita i predacije riba na promjenu uvjeta okoliša

“Raspetljavanje” hranidbenih mreža u litoralu plitkih jezera umjerene zone

Elucidation of food web interactions provides a better understanding of ecosystem functioning, indicates anthropogenic impacts which often cause alterations in environmental conditions and deterioration in feeding networks in terrestrial and aquatic ecosystems. The importance of microfauna and macroinvertebrates in the littoral zones of shallow waters has been poorly studied regarding their trophic interactions. This study compares invertebrate assemblage and food web interactions among epiphyton, zooplankton and benthic macroinvertebrates across structural heterogeneity in the littoral zone of three temperate shallow water bodies. Submerged and structurally-complex stands of Ceratophyllum demersum inhabited a higher abundance of cladocerans and supported a higher diversity and biomass of epiphytic protozoans and invertebrates than floating-leaved Nuphar lutea stands. Analysis of the ecosystem functioning illustrated the increased biomass of macroinvertebrate predators and a preference of predation over planktonic crustaceans in more complex macrophyte stands. Food webs displayed higher complexity and size with habitat heterogeneity, while epiphyton and zooplankton shared an important fraction in food resources among the invertebrate trophic network. Results of food web modelling indicated zooplankton and epiphyton as more vulnerable to invertebrate predation in the complex submerged macrophytes than in the floating-leaved macrophyte stands. Integrated approaches to community, ecosystem and food webs in explanation of complex trophic interactions in the littoral zones confirmed an increase in diversity and food-web functional complexity with structural heterogeneity of microhabitats.Razjašnjenje interakcija u hranidbenoj mreži omogućuje bolje razumijevanje funkcioniranja ekosustava te indikaciju antropogenih učinaka koji često uzrokuju promjene uvjeta okoliša i narušavanje hranidbene mreže kopnenih i vodenih ekosustava. Trofičke interakcije mikrofaune i makrozoobentosa slabo su proučavane u priobalnim (litoralnim) zonama plitkih vodenih tijela. Cilj ovog rada je usporediti interakcije beskralježnjaka i izvora hrane, uključujući epifiton, zooplankton i makrozoobentos u strukturno heterogenim litoralnim zonama triju plikih jezera umjerenog pojasa. U submerznim i strukturno složenim makrofitskim sastojinama vrste Ceratophyllum demersum rašljoticalci su razvili populacije velike brojnosti, a također je u njima zbilježena veća raznolikost i biomasa epifitskih protozoa i beskralježnjaka u usporedbi sa sastojinama plutajuće vrste Nuphar lutea. Analiza funkcioniranja ekosustava ukazivala je na to da je u heterogenim makrofitskim sastojinama povećana biomasa makrozoobentoskih predatora i izraženija je njihova predacija nad planktonskim rakovima. Hranidbene mreže bile su složenije u heterogenima staništima, a epifiton i zooplankton imali su važan udio u hranidbenim resursima unutar hranidbene mreže beskralježnjaka. Modeliranje hranidbenih mreža inidicira veću ranjivost zooplanktona i epifitona na predaciju beskralježnjaka u kompleksnijim, submerznim, makrofitskim sastojinama u odnosu na sastojine plutajućih makrofita. Integrirani pristup s aspekta ekologije biocenoza, ekosustava i hranidbenih mreža u objašnjenju složenih trofičkih interakcija u litoralnoj zoni potvrđuje povećanje raznolikosti i kompleksnosti hranidbenih mreža sa strukturalnom heterogenošću mikrostaništa

Impact of submersed macrophytes and fish predation on the structure of zooplankton in shallow eutrophic lakes

Eutrofikacija i klimatske promjene mijenjaju funkcioniranje plitkih jezera te zahtijevaju provođenje restauracije, posebno ekološki prihvatljivim biološkim metodama promjene hranidbene mreže jezera ili održavanja submerznih makrofita. Cilj ovoga rada bio je utvrditi utjecaj submerznih makrofita, predacijskog pritiska riba, abiotičkih čimbenika i raspoloživosti hrane na strukturu zooplanktona, uključujući prehrambene skupine, veličinsku strukturu i fekunditet. Istraživanje je provedeno u dva jezera – prozirnom sa submerznim makrofitima i mutnom bez makrofita u kojem je i postavljen in situ mezokozmos. Rezultatima rada se utvrdio značaj utjecaja submerznih makrofita i predacije riba na promjene uvjeta okoliša i strukturu zooplanktona u jezerima sličnog stupnja trofije. Rezultati mezokozmosa ukazuju na sposobnost submerznih makrofita da, u relativno kratkom razdoblju, doprinesu poboljšanju kvalitete vode i održanju ravnoteže ekosustava plitkih jezera. Submerzni makrofiti su pružili sklonište od vizualnih predatora većim algivornim rašljoticalcima, koji hranjenjem smanjuju abundanciju alga, čime je potvrđena opravdanost primjene ove biološke metode u restauraciji plitkih eutrofnih jezera.Eutrophication and climate change alter functioning of shallow lake ecosystems and demand for lake restoration, particularly by environmentally acceptable biological methods such as food web biomanipulation or maintaining submerged macrophyte stands. The aim of this thesis was to determine the impact of submerged macrophytes, fish predation, abiotic parameters and food availability on zooplankton structure, including zooplankton functional feeding guilds, size structure and fecundity. The research was conducted in two oxbow lakes – transparent lake with, and turbid lake without submerged macrophytes, in which an in situ mesocosm was set up. Results demonstrated the importance of submerged macrophytes and fish predation impacts on dissimilarities and alteration of environmental conditions zooplankton structure in lakes of similar trophic status. Mesocosm results demonstrated the ability of submerged macrophytes to improve water quality and contribute to maintaining the balance of shallow lake ecosystem. Submerged macrophytes provided refuge from visual predators to large algivorous Cladocera that can reduce phytoplankton abundance though grazing, thus confirming applicability of this biological method in shallow eutrophic lake restauration

Impact of submersed macrophytes and fish predation on the structure of zooplankton in shallow eutrophic lakes

Eutrofikacija i klimatske promjene mijenjaju funkcioniranje plitkih jezera te zahtijevaju provođenje restauracije, posebno ekološki prihvatljivim biološkim metodama promjene hranidbene mreže jezera ili održavanja submerznih makrofita. Cilj ovoga rada bio je utvrditi utjecaj submerznih makrofita, predacijskog pritiska riba, abiotičkih čimbenika i raspoloživosti hrane na strukturu zooplanktona, uključujući prehrambene skupine, veličinsku strukturu i fekunditet. Istraživanje je provedeno u dva jezera – prozirnom sa submerznim makrofitima i mutnom bez makrofita u kojem je i postavljen in situ mezokozmos. Rezultatima rada se utvrdio značaj utjecaja submerznih makrofita i predacije riba na promjene uvjeta okoliša i strukturu zooplanktona u jezerima sličnog stupnja trofije. Rezultati mezokozmosa ukazuju na sposobnost submerznih makrofita da, u relativno kratkom razdoblju, doprinesu poboljšanju kvalitete vode i održanju ravnoteže ekosustava plitkih jezera. Submerzni makrofiti su pružili sklonište od vizualnih predatora većim algivornim rašljoticalcima, koji hranjenjem smanjuju abundanciju alga, čime je potvrđena opravdanost primjene ove biološke metode u restauraciji plitkih eutrofnih jezera.Eutrophication and climate change alter functioning of shallow lake ecosystems and demand for lake restoration, particularly by environmentally acceptable biological methods such as food web biomanipulation or maintaining submerged macrophyte stands. The aim of this thesis was to determine the impact of submerged macrophytes, fish predation, abiotic parameters and food availability on zooplankton structure, including zooplankton functional feeding guilds, size structure and fecundity. The research was conducted in two oxbow lakes – transparent lake with, and turbid lake without submerged macrophytes, in which an in situ mesocosm was set up. Results demonstrated the importance of submerged macrophytes and fish predation impacts on dissimilarities and alteration of environmental conditions zooplankton structure in lakes of similar trophic status. Mesocosm results demonstrated the ability of submerged macrophytes to improve water quality and contribute to maintaining the balance of shallow lake ecosystem. Submerged macrophytes provided refuge from visual predators to large algivorous Cladocera that can reduce phytoplankton abundance though grazing, thus confirming applicability of this biological method in shallow eutrophic lake restauration

Effects of emergent vegetation on zooplankton and epiphyton communities in oxbow lakes of river Krapina

U istraživanju zooplanktona i epifitona, provedenog tijekom ljetnog razdoblja 2008. godine u dva rukavca rijeke Krapine, bile su obuhvaćene skupine kolnjaka (Rotifera), veslonožaca (Copepoda) i rašljoticalaca (Cladocera). Uzorci zooplanktona su uzimani u svakom jezeru u zoni slobodne vode i litorala. Epifiton je strugan s makrofita (Iris pseudacorus i Mentha aquatica) uzetih na postajama litorala. Osnovne hipoteze ovog rada bile su: (i) širina litoralne zone i prozirnost vode utječu na horizontalnu raspodjelu zooplanktona u plitkim jezerima; (ii) širina zone makrofita te struktura stabljike utječu na sastav epifitona. Ciljevi istraživanja bili su: 1) analizirati razlike kvalitativnog i kvantitativnog sastava zooplanktona slobodne vode i litorala u rukavcima s različitom prozirnošću vode; 2) analizirati utjecaj abiotičkih i biotičkih čimbenika na sastav zooplanktona u zoni slobodne vode i u litoralnoj zoni; 3) utvrditi utjecaj abiotičkih i biotičkih čimbenika na kvalitativni i kvantitativni sastav epifitona. Fizičko-kemijski čimbenici te izvori hrane nisu se značajno razlikovali unutar rukavaca. Između rukavaca zabilježena je značajna razlika u prozirnosti vode i koncentraciji klorofila a koja je utjecala na sastav zajednica. Manja prozirnost vode u RK1 uvjetovana je užom zonom makrofita i većom koncentracijom suspendiranih organskih tvari, dok je veća prozirnost u RK2 uvjetovana širom zonom makrofita i sastavom zooplanktona. U sastavu zooplanktona obaju rukavaca dominirale su od Rotifera vrste roda Polyarthra te vrsta Keratella cohlearis, od Copepoda ličinački stadiji. Cladocera su u RK1 bili zastupljeni manjim, a u RK2 većim vrstama. Algivorni Rotifera i Copepoda dominirali su u slobodnoj vodi, za što je bila ključna raspoloživost hrane. Predacijski pritisak riba (vizualnih predatora) bio je ublažen manjom prozirnošću vode i višim stupnjem trofije u RK1. Brojnost vrste Bosmina longirostris u slobodnoj zoni određena je kompeticijom s vrstom K. cochlearis i prozirnošću vode, odnosno, predacijskim pritiskom riba, što je pogotovo vidljivo u rukavcu s većom prozirnošću vode i izraženijim predacijskim pritiskom riba - RK2. Veća prozirnost ukazuje na niži stupanj trofije RK2 u odnosu na RK1, što se očitovalo i u manjoj brojnosti zooplanktona. U jezeru sa širom zonom makrofita brojnost svojti epifitona bila je veća. Također, veća brojnost epifitona zabilježena je na strukturno složenijim stabljikama vodene metvice u odnosu na jednostavne stabljike irisa. Raznolikost vrsta makrofita i šira zona makrofita pozitivno utječu na raznolikost i brojnost epifitona.The research of zooplankton and epiphyton was conducted in the summer of 2008 in two oxbow lakes of the river Krapina. The investigation included rotifers (Rotifera), cladocerans (Cladocera) and copepods (Copepoda). Zooplankton samples were collected in free-water zone and littoral of each lake. Epiphyton samples were scraped from plants surfaces (Iris pseudacorus and Mentha aquatica) taken at the littoral stations. The following hypotheses were set: (i) width of littoral zone and water clarity affect horizontal distribution of zooplankton in shallow lakes; (ii) width of macrophyte bed and plant stem structure affect epiphyton composition. The research goals were: 1) to analyse qualitative and quantitative differences of zooplankton composition both in free-water and in littoral zone of lakes with different water clarity; 2) to analyse effects of environmental and biotic factors on both free-water and littoral zooplankton composition; 3) to determine effects of environmental and biotic factors on both the qualitative and quantitative epiphyton composition. Environmental factors and food resources did not differ significantly within the lakes. However, between the lakes the significant difference in water clarity and chlorophyl a was determined. RK1 smaller water clarity was induced by a narrower macrophyte bed and a greater concentration of suspended organic matter, while RK2 greater water clarity was induced by a wider macrophyte bed zooplankton composition. In zooplankton composition of both lakes dominant Rotifera were species of genus Polyarthra and species Keratella cochlearis and Copepoda larval stages. Cladocera were represented with smaller species in RK1, while in RK2 larger species were found. Algivoric Rotofera and Copepoda were dominant in free-water zones because of food availability. Fish predatory pressure was reduced by smaller water clarity and higher trophy state in RK1. Abundance of Bosmina longirostris in free-water was determined by food competition with K. Cochlearis and by water clarity, i.e. fish predation which was particurlary visible in RK2 due to a greater water clarity. The higher water clarity indicates lesser trophy level of RK2 in relation to RK1, which was manifested in a smaller zooplankton abundancy. The lake with the wider macrophyte bed had a greater number of epiphyton species. The greater epiphyton abundancy was detected on the morphologicaly more complex stems of Mentha aquatica compared to the simpler ones of Iris pseudacorus. Plant species diversity and wider macrophyte bed intensly affect epiphyton diversity and abundance

Impact of submersed macrophytes and fish predation on the structure of zooplankton in shallow eutrophic lakes

Eutrofikacija i klimatske promjene mijenjaju funkcioniranje plitkih jezera te zahtijevaju provođenje restauracije, posebno ekološki prihvatljivim biološkim metodama promjene hranidbene mreže jezera ili održavanja submerznih makrofita. Cilj ovoga rada bio je utvrditi utjecaj submerznih makrofita, predacijskog pritiska riba, abiotičkih čimbenika i raspoloživosti hrane na strukturu zooplanktona, uključujući prehrambene skupine, veličinsku strukturu i fekunditet. Istraživanje je provedeno u dva jezera – prozirnom sa submerznim makrofitima i mutnom bez makrofita u kojem je i postavljen in situ mezokozmos. Rezultatima rada se utvrdio značaj utjecaja submerznih makrofita i predacije riba na promjene uvjeta okoliša i strukturu zooplanktona u jezerima sličnog stupnja trofije. Rezultati mezokozmosa ukazuju na sposobnost submerznih makrofita da, u relativno kratkom razdoblju, doprinesu poboljšanju kvalitete vode i održanju ravnoteže ekosustava plitkih jezera. Submerzni makrofiti su pružili sklonište od vizualnih predatora većim algivornim rašljoticalcima, koji hranjenjem smanjuju abundanciju alga, čime je potvrđena opravdanost primjene ove biološke metode u restauraciji plitkih eutrofnih jezera.Eutrophication and climate change alter functioning of shallow lake ecosystems and demand for lake restoration, particularly by environmentally acceptable biological methods such as food web biomanipulation or maintaining submerged macrophyte stands. The aim of this thesis was to determine the impact of submerged macrophytes, fish predation, abiotic parameters and food availability on zooplankton structure, including zooplankton functional feeding guilds, size structure and fecundity. The research was conducted in two oxbow lakes – transparent lake with, and turbid lake without submerged macrophytes, in which an in situ mesocosm was set up. Results demonstrated the importance of submerged macrophytes and fish predation impacts on dissimilarities and alteration of environmental conditions zooplankton structure in lakes of similar trophic status. Mesocosm results demonstrated the ability of submerged macrophytes to improve water quality and contribute to maintaining the balance of shallow lake ecosystem. Submerged macrophytes provided refuge from visual predators to large algivorous Cladocera that can reduce phytoplankton abundance though grazing, thus confirming applicability of this biological method in shallow eutrophic lake restauration

Zooplankton structure in two interconnected ponds: similarities and differences

The research of zooplankton diversity, abundance and trophic structure was conducted during the summer period in pelagial zone on the longitudinal profile of the Sutla River Backwater. Investigated site consists of two interconnected basins: transparent Upper Basin with submerged macrophytes and turbid Lower Basin without macrophytes in the littoral zone. In the Upper Basin, abundance and diversity of zooplankton in the pelagial was higher in comparison to the Lower Basin, with prevailing species of genus Keratella as microfilter-feeder, and genera of Polyartha and Trihocerca as macrofilter-feeder rotifers. On the contrary, in the Lower Basin, crustaceans dominated in abundance. Microfilter-feeder cladoceran (Bosmina longirostris) and larval and adult stages of macrofilter-feeder copepod (Macrocyclops albidus) prevailed in the Lower Basin. Fish predation pressure was more pronounced in the pelagial of the Upper Basin, indicated by low cladoceran abundance in the surface layer. Although the studied basins were interconnected, results indicate significant (Mann-Whitney U test, p < 0.05) differences in the zooplankton structure as a potential result of the macrophyte impact on environmental conditions and fish predation pressure

Zooplankton structure in two interconnected ponds: similarities and differences

The research of zooplankton diversity, abundance and trophic structure was conducted during the summer period in pelagial zone on the longitudinal profile of the Sutla River Backwater. Investigated site consists of two interconnected basins: transparent Upper Basin with submerged macrophytes and turbid Lower Basin without macrophytes in the littoral zone. In the Upper Basin, abundance and diversity of zooplankton in the pelagial was higher in comparison to the Lower Basin, with prevailing species of genus Keratella as microfilter-feeder, and genera of Polyartha and Trihocerca as macrofilterfeeder rotifers. On the contrary, in the Lower Basin, crustaceans dominated in abundance. Microfilter-feeder cladoceran (Bosmina longirostris) and larval and adult stages of macrofilter-feeder copepod (Macrocyclops albidus) prevailed in the Lower Basin. Fish predation pressure was more pronounced in the pelagial of the Upper Basin, indicated by low cladoceran abundance in the surface layer. Although the studied basins were interconnected, results indicate significant (Mann-Whitney U test, p < 0.05) differences in the zooplankton structure as a potential result of the macrophyte impact on environmental conditions and fish predation pressure.Istraživanje raznolikosti, abundancije i trofičke strukture zooplanktona provedeno je tijekom vegetacijskog razdoblja na pelagičkim postajama longitudinalnog profila rukavca rijeke Sutle koji se sastoji od dva međusobno povezana bazena. Gornji bazen veće je prozirnosti i sa submerznim sastojinama makrofita, Donji bazen veće je mutnoće i bez makrofita. U Gornjem bazenu, brojnost i raznolikost zooplanktona u pelagijalu je bila veća u odnosu na Donji bazen, a prevladavali su kolnjaci, detritivorni-mikrofiltratori roda Keratella i algivorni-makrofiltratori rodova Polyartha i Trihocerca. U Donjem bazenu brojnost planktonskih rakova bila je veća u odnosu na Gornji bazen, a prevladavali su mikrofiltratorski rašljoticalci (Bosmina longirostris) te makrofiltratorski ličinački i adultni stadiji veslonožaca (Macrocyclops albidus). Predacijski pritisak riba bio je izraženiji u pelagijalu Gornjeg bazena, na što ukazuje manja brojnost Cladocera u površinskom sloju. Iako su istraživani bazeni međusobno povezani, rezultati rada ukazuju na značajne razlike (Mann-Whitney U test, p < 0.05) u strukturi zooplanktona kao rezultat utjecaja makrofita i predacije riba na promjenu uvjeta okoliša