Zooplanktoni toitumise mõju madalate eutroofsete järvede ökosüsteemile

Käesoleva töö eesmärgiks oli uurida zooplanktoni toitumise mõju füto- ja bakterplanktoni kooslustele erinevas tasakaaluseisundis olevate madalate eutroofsete järvede toiduahelas. Sesoonselt hinnati zooplanktoni toitumise mõju fütoplanktoni üldhulgale ja primaarproduktsioonile. Süvendatult uuriti ja võrreldi erinevate zooplanktoni suurus- ja taksonoomiliste rühmade (heterotroofsed viburloomad, ripsloomad, keriloomad ja vesikirbulised) toitumise mõju bakterplanktonile ja väikesemõõtmelisele fütoplanktonile. Töö üheks eesmärgiks oli täiendada suhteliselt puudulikku informatsiooni peamiste füto- ja bakterplanktonit tarbivate metazooplanktoni liikide kohta madalates eutroofsetes parasvöötmejärvedes. Põhiline osa uurimustest teostati Võrtsjärvel, tulemusi võrreldi kahe teise madala järvega (Prossa ja Kaiavere). Töö tulemusena leiti järgmist: 1. Madalates makrofüüdienamusega järvedes võib zooplanktoni toitumine oluliselt mõjutada fütoplanktoni sesoonset dünaamikat ning põhjustada selgevee perioodi tekkimist (näiteks Prossa järves). Seevastu fütoplanktonienamusega madalates järvedes, kus fütoplanktoni koosluse moodustavad valdavalt suured zooplanktonile söödamatud vetikad, suudab zooplankton süüa vaid väikese osa kogu fütoplanktoni biomassist (Võrtsjärves vähem kui 5%). Tugevamat ärasöömismõju avaldab zooplankton nano-suurusega fütoplanktonile, millest suurusvahemik 5-15 μm tundub olevat tähtsaim vetikatoit peamistele fütoplanktonit söövatele zooplankteritele madalates eutroofsetes järvedes (ripsloomad, Polyarthra spp., Bosmina longirostris, Chydorus sphaericus ja Daphnia cucullata; I, II). 2. Madalates eutroofsetes järvedes avaldab zooplankton tugevamat ärasöömismõju fütoplanktonile enamasti kevadel kui vetikate biomass on veel madal ning sisaldab suhteliselt rohkem väikeseid zooplanktonile söödava suurusega rakke. Esimesteks fütoplanktoni sööjateks sel ajal on arvukalt planktonis esinevad ripsloomad ja keriloomad (I, II). 3. Madatalate eutroofsete järvede zooplanktonis domineeriv ripsloomade ja keriloomade kooslus võib olla peamine fütoplanktoni sööja kogu vegetatsiooniperioodi vältel ning nende rühmade osakaal fütoplanktoni biomassi vähendamisel võib moodustada üle 60% kogu zooplanktoni mõjust (II).4. Madatalates eutroofsetes järvedes esinev arvukas keriloomade kooslus, mis sisaldab kõrge toitumiskiirusega liike (nagu Filinia longiseta, Pompolyx complanata, Conochilus unicornis) võib olla tähtsaimaks bakterite sööjaks metazooplanktoni rühmade hulgas. Vesikirbuliste koosluses sageli domineeriv väikesekehaline C. sphaericus võib olla tähtsaimaks fütoplanktonit ja baktereid söövaks metazooplankteriks liigi tasandil (III). 5. Madalates eutroofsetes järvedes võivad ripsloomad olla oluliseks toiduahela komponendiks, olles peamised bakterite ja väikeste vetikate sööjad ning tarbides märgatava osa bakteriproduktsioonist, samas kui metazooplanktoni osa vetikate ja bakterit söömisel võib jääda tagasihoidlikuks (IV). 6. Madal metazooplanktoni toitumise mõju ning kõrge ripsloomade osakaal zooplanktonis ja toiduallikate tarbimisel näitab mikroobse toiduahela suurt tähtsust madalate eutroofsete järvede ökosüsteemi funktsioneerimisel (III, IV).Funding for this research was provided by a target-financed project (0362480s03) of the Estonian Ministry of Education and Research, by grants 4080 and 5738 from the Estonian Science Foundation, and by the European Commission’s Environment and Sustainable Development Program under contracts EVK1-CT-1999-39 (ECOFRAME) and EVK1-CT-2002-00121 (CLIME)

Prey selection and growth in 0+ Eurasian perch Perca fluviatilis L. in littoral zones of seven temperate lakes

We studied the relationships between the planktonic food base and feeding patterns of juvenile mid-summer/ early autumn Eurasian perch Perca fluviatilis L., a common predatory freshwater fish in large parts of Europe and Asia. The feeding of 0+ perch was studied during summer and autumn in littoral habitats of seven lakes with different environmental conditions –four Latvian (Auciema, Riebinu, Vārzgūnes, Laukezers) and three Estonian (Kaiavere, Prossa and Akste) lakes. Simultaneously, the abundance, biomass and structure of zooplankton communities were examined. We focused on the littoral areas because many studies in lakes suggest that littoral habitats are particularly important for 0+ fish growth and survival. We were interested in the question: can the diet and growth of 0+ perch be explained by zooplankton community structure? We also presumed that if the amount of zooplankton is low, more benthic invertebrates will be consumed by 0+ perch. Opposite to expectations, we found that zooplankton always counted for over 90% of diet biomass in perch. There were also clear correlations between the zooplankton biomass in a given lake, the zooplankton biomass in 0+ perch stomachs, and the fish growth rate. The study also suggested that nutrient enrichment can positively impact the 0+ perch feeding conditions in lakes.The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation “Institute for Environmental Solutions”. Funding for this project was also provided by the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963 (TREICLAKE “Towards Research Excellence and Innovation Capacity in Studying Lake Ecosystems Functional Structures and Climate Change Impact”).The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation “Institute for Environmental Solutions”. Funding for this project was also provided by the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963 (TREICLAKE “Towards Research Excellence and Innovation Capacity in Studying Lake Ecosystems Functional Structures and Climate Change Impact”)

How warming and other stressors affect zooplankton abundance, biomass and community composition in shallow eutrophic lakes

We aimed to investigate the influence of environmental factors and predict zooplankton biomass and abundance in shallow eutrophic lakes. We employed time series of zoo- plankton and environmental parameters that were measured monthly during 38 years in a large, shallow eutrophic lake in Estonia to build estimates of zooplankton community metrics (cladocerans, copepods, rotifers, ciliates). The analysis of historical time series revealed that air temperature was by far the most important variable for explaining zooplankton biomass and abundance, followed, in decreasing order of importance, by pH, phytoplankton biomass and nitrate concentration. Models constructed with the best predicting variables explained up to 71% of zooplankton biomass variance. Most of the predictive variables had opposing or antagonistic interactions, often mitigating the effect of temperature. In the second part of the study, three future climate scenarios were developed following different Intergovernmental Panel on Climate Change (IPCC) tem- perature projections and entered into an empirical model. Simulation results showed that only a scenario in which air temperature stabilizes would curb total metazooplankton biomass and abundance. In other scenarios, metazooplankton biomass and abundance would likely exceed historical ranges whereas ciliates would not expand. Within the metazooplankton community, copepods would increase in biomass and abundance, whereas cladocerans would lose in biomass but not in abundance. These changes in the zooplankton community will have important consequences for lake trophic structure and ecosystem functioning.This research was supported by the Estonian Research Council Grants PSG32, PRG709 and institutional research funding IUT 21-2 of the Estonian Ministry of Education and Research.This research was supported by the Estonian Research Council Grants PSG32, PRG709 and institutional research funding IUT 21-2 of the Estonian Ministry of Education and Research

Changes in nutrient concentration and water level affect the microbial loop: a multi-seasonal mesocosm experiment

Eutrophication and lake depth are of key importance in structuring lake ecosystems. To elucidate the effect of contrasting nutrient concentrations and water levels on the microbial community, we manipulated water depth and nutrients in a mesocosm experiment in north temperate Estonia and followed the microbial community dynamics during a 6-month period. We used two nutrient levels crossed with two water depths, each represented by four replicates. We found treatment effects on the microbial food web structure, with nutrients having a positive and water depth a negative effect on bacterial biomass, heterotrophic nanoflagellates (HNF) and metazooplankton biomass. Nutrients and water depth had both positive impacts on phytoplankton biomass. Bacterivorous ciliates had lowest biomass in shallow and nutrient rich mesocosms, whilst predaceous ciliates had highest biomass here, influencing trophic interactions in the microbial loop. Overall, increased nutrient concentrations and decreased water level resulted in an enhanced bacterial biomass and a decrease in their main grazers. These differences appeared to reflect distinctive regulation mechanisms inside the protozoan community and in the trophic interactions in the microbial loop community.This work was supported by EU 7FP Theme 6 projects MARS (Managing Aquatic ecosystems and water Resources under multiple Stress, Contract No. 603378), Estonian Ministry of Education and Research (IUT 21-02), Estonian Research Council grant PRG709, Estonian University of Life Sciences (P190258PKKH) and Swiss Grant for Programme "Enhancing public environmental monitoring capacities". This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Erik Jeppesen was also supported by the TÜBITAK program BIDEB2232 (project 118C250).This work was supported by EU 7FP Theme 6 projects MARS (Managing Aquatic ecosystems and water Resources under multiple Stress, Contract No. 603378), Estonian Ministry of Education and Research (IUT 21-02), Estonian Research Council grant PRG709, Estonian University of Life Sciences (P190258PKKH) and Swiss Grant for Programme "Enhancing public environmental monitoring capacities". This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Erik Jeppesen was also supported by the TÜBITAK program BIDEB2232 (project 118C250)

Keystone species Chydorus sphaericus in shallow eutrophic Lake Võrtsjärv (Estonia) – 56 years of continuous zooplankton monitoring and research

Presentation at the 11th International Shallow Lakes Conference, Estonia 11.-16.06.2023.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963, by Estonian Ministry of the Environment through the state monitoring programme, and also from the Estonian Research Council grant PRG1167.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963, by Estonian Ministry of the Environment through the state monitoring programme, and also from the Estonian Research Council grant PRG1167

Larval and juvenile perch feeding in some Estonian and Latvian study lakes : [poster]

The presentation took place at the Lahti Lakes 2021 Symposium.The research is a part of the project „Fish feeding conditions in lakes with different planktonic food web structure and macrovegetation “(MICROFISH), No.1.1.1.2/VIAA/1/18/301. Agreement with State Education Development Agency of the Republic of Latvia No. Programme number 1.1.1.2/16/I/001. The project has received funding from the European Regional Development Fund, from the State budget of the Republic of Latvia, from the foundation „Institute for Environmental Solutions” and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Greatest thanks to PhD Priit Zingel.The research is a part of the project „Fish feeding conditions in lakes with different planktonic food web structure and macrovegetation “(MICROFISH), No.1.1.1.2/VIAA/1/18/301. Agreement with State Education Development Agency of the Republic of Latvia No. Programme number 1.1.1.2/16/I/001. The project has received funding from the European Regional Development Fund, from the State budget of the Republic of Latvia, from the foundation „Institute for Environmental Solutions” and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Greatest thanks to PhD Priit Zingel

The influence of macrophyte ecological groups on food web components of temperate freshwater lakes

Aquatic macrophyte taxonomic composition, species abundance and cover determine the physical structure, complexity and heterogeneity of aquatic habitats – the structuring role of macrophytes. These traits influence richness, distribution, feeding and strength of the relationships between food web communities in lakes. The aim of this study was to determine how lakes with different dominating macrophyte ecological groups affect planktonic food web components, emphasising the influence on young of year (YOY) fish and large (≥1 +) fish community. We hypothesised that different dominating macrophyte ecological groups have different structural effects on food web components and YOY fish growth, abundance and feeding. Studied lakes categorised into three different macrophyte ecological groups – lakes dominated by emergent, floating+floating-leaved or submerged vegetation. We found that all dominating ecological groups had a strong influence on plankton communities (except heterotrophic bacterioplankton and nanoflagellates), YOY fish and large fish. Floating-leaved plant dominance was positively related to planktonic food web structure and YOY fish weight, length, abundance and the consumption of zooplankton as a prey of all major species of YOY fishes. Larger fish tended to favour the presence of emergent vegetation. This conclusion has important implications for local managers and conservationists in respect to the maintenance and protection of littoral habitats and fish resources.The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation “Institute for Environmental Solutions”. Also, this project has received funding from the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963.The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation “Institute for Environmental Solutions”. Also, this project has received funding from the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963

Macroecological patterns of resilience inferred from a multinational, synchronized experiment

The likelihood of an ecological system to undergo undesired regime shifts is expected to increase as climate change effects unfold. To understand how regional climate settings can affect resilience; i.e., the ability of an ecosystem to tolerate disturbances without changing its original structure and processes, we used a synchronized mesocosm experiment (representative of shallow lakes) along a latitudinal gradient. We manipulated nutrient concentrations and water levels in a synchronized mesocosm experiment in different climate zones across Europe involving Sweden, Estonia, Germany, the Czech Republic, Turkey and Greece. We assessed attributes of zooplankton communities that might contribute to resilience under different ecological configurations. We assessed four indicator of relative ecological resilience (cross-scale, within-scale structures, aggregation length and gap size) of zooplankton communities, inferred from discontinuity analysis. Similar resilience attributes were found across experimental treatments and countries, except Greece, which experienced severe drought conditions during the experiment. These conditions apparently led to a lower relative resilience in the Greek mesocosms. Our results indicate that zooplankton community resilience in shallow lakes is marginally affected by water level and the studied nutrient range unless extreme drought occurs. In practice, this means that drought mitigation could be especially challenging in semi-arid countries in the future

Causal networks of phytoplankton diversity and biomass are modulated by environmental context

Untangling causal links and feedbacks among biodiversity, ecosystem functioning, and environmental factors is challenging due to their complex and context-dependent interactions (e.g., a nutrient-dependent relationship between diversity and biomass). Consequently, studies that only consider separable, unidirectional effects can produce divergent conclusions and equivocal ecological implications. To address this complexity, we use empirical dynamic modeling to assemble causal networks for 19 natural aquatic ecosystems (N24◦~N58◦) and quantified strengths of feedbacks among phytoplankton diversity, phytoplankton biomass, and environmental factors. Through a cross-system comparison, we identify macroecological patterns; in more diverse, oligotrophic ecosystems, biodiversity effects are more important than environmental effects (nutrients and temperature) as drivers of biomass. Furthermore, feedback strengths vary with productivity. In warm, productive systems, strong nitrate-mediated feedbacks usually prevail, whereas there are strong, phosphate-mediated feedbacks in cold, less productive systems. Our findings, based on recovered feedbacks, highlight the importance of a network view in future ecosystem management

Causal networks of phytoplankton diversity and biomass are modulated by environmental context

Untangling causal links and feedbacks among biodiversity, ecosystem functioning, and environmental factors is challenging due to their complex and context-dependent interactions (e.g., a nutrient-dependent relationship between diversity and biomass). Consequently, studies that only consider separable, unidirectional effects can produce divergent conclusions and equivocal ecological implications. To address this complexity, we use empirical dynamic modeling to assemble causal networks for 19 natural aquatic ecosystems (N24◦~N58◦) and quantified strengths of feedbacks among phytoplankton diversity, phytoplankton biomass, and environmental factors. Through a cross-system comparison, we identify macroecological patterns; in more diverse, oligotrophic ecosystems, biodiversity effects are more important than environmental effects (nutrients and temperature) as drivers of biomass. Furthermore, feedback strengths vary with productivity. In warm, productive systems, strong nitrate-mediated feedbacks usually prevail, whereas there are strong, phosphate-mediated feedbacks in cold, less productive systems. Our findings, based on recovered feedbacks, highlight the importance of a network view in future ecosystem management