Järvedes valitsevad tingimused veetaimestiku kujundajatena

Macrophytes play an important role in lake ecosystems, which provisionally can be divided into an active role consisting of modifying in-lake processes and creating habitat for other groups of biota, and a passive role where macrophytes themselves are subjected to forcing factors within lake environments. The active role of macrofytes as providers of food, shelter and habitat is predominant in small and shallow lakes where the littoral area colonized by plants constitutes a large part of the lake’s total area. With increasing lake area and depth, the active role is gradually declining and replaced by a more passive role in large lakes in which macrophyte distribution and composition are strongly controlled by lake morphometry and meteorological factors. As small and shallow lakes form the majority in the world’s lake population, research has paid more attention to studying the active role of macrophytes. The present thesis, however, has put the emphasis on the opposite aspects – the questions how the in-lake conditions affect the distribution of species, plant architecture and community composition, and how these parameters can be used in lake status assessment. The materials for the present thesis have been collected during 14 years from 9 Estonian lakes, but the bulk of the data originates from Võrtsjärv and two smaller lakes, Prossa and Kaiavere, located in the Vooremaa drumlin area. The spectrum of macrophyte related topics analysed and discussed in the original publications is wide ranging from eco-physiological aspects and aspects of autecology to population ecology and synecology. Given the broad thematic spread of the underlying papers, the synthesis part of the thesis follows the format of a review paper in which the original papers are integraded by references. This format was selected to avoid unnecessary repetition of what was already written in the papers and to enable a more complete overview of the various aspects of the topic, including those not directly covered by the original papers. The complex of factors in lakes can be divided into three major groups – physical, chemical and biological, which have, correspondingly, limnological, metabolic and biotic effects on macrophytes. Limnological effects on macrophytes are expressed through physical parameters of water and sediments, water movements, and conditions of light and temperature, metabolic effects are related to nutrient cycles and production of organic matter, whereas biotic effects are the result of mutual relationships within the plant community or between plants and other groups of biota. These groups of factors form a complex structure which influences on aquatic macrophytes are reviewed in the synthesis part of the thesis in both spatial and temporal scales. The sensitivity of macrophytes to environmental conditions is the basis for their indicator power enabling to use plant community metrics for assessing the ecological status and its trends in water bodies. One of the major results of the studies was the finding out of the complex of factors determining the structure and distribution of macrophytes in Lake Võrtsjärv. Nutrient availability and the effect of prevailing winds play the leading roles in this lake, which owing to the shape of the lake create a distinctive polarization of the littoral vegetation both in a north-south and a west-east gradient. A comparison with historical data from the beginning of the 20th century showed the change in the community composition of macrophytes being the largest among all biotic groups of the lake. Eutrophication resulting from riverine nutrient loadings was proved as the major cause of these changes. A retrospective analysis of satellite images for the last 20 years showed that the changes continue as evidenced by the rapid expansion of the reed belt with an average annual rate of 2.2 m and especially pronounced around the mouths of inflowing rivers. The contribution of macrophyte production to the total primary production over the vegetation period reached 35.5% in Lake Võrtsjärv but was only 10% in the deeper Lake Peipsi. Studies of the two lakes in Vooremaa revealed that the lake size dependent wind impact supports the shift of the balance from the macrophyte dominance to phytoplankton dominance and showed how the resulting differences in light climate change the architecture of submerged plants. Järve ökosüsteemis on veetaimestikul väga oluline roll, mida võib tinglikult jagada aktiivseks, kus veetaimed mõjutavad järves toimuvaid protsesse ja kujundavad elutingimusi teistele järve asukatele ning passiivseks, kus veetaimed on ise mõjutatud järves toimuvatest protsessidest. Väikestes ja madalates järvedes, kus taimedega asustatud litoraal moodustab suure osa järve kogupindalast, on ülekaalus taimede aktiivne funktsioon nii toidu tootja, varje pakkuja kui elupaiga loojana, kuid enamasti see ülekaal kahaneb nii järve pindala ja sügavuse kasvades ning suurtes järvedes on taimestik enam allutatud ilmastikust ja järvenõo kujust sõltuvatele teguritele. Kuna suurem osa järvi maailmas on väikese pindalaga ning madalad, on suurem rõhuasetus veekogude taimestiku uuringutes langenud veetaimestiku aktiivse rolli selgitamisele veekogus. Käesolev töö keskendub vastupidisele aspektile – küsimustele, kuidas mõjutavad järves valitsevad tingimused taimeliikide levikut, nende morfomeetrilisi näitajaid ja taimekoosluste struktuuri ja kuidas neid näitajaid saab kasutada järves valitsevate tingimuste hindamisel. Käesoleva töö materjal on kogutud 14 aasta jooksul kokku üheksast Eesti järvest, kuid peamine andmestik pärineb Võrtsjärvest ja kahest Vooremaa järvest, Prossast ja Kaiaverest. Töös kirjeldatud teemade ring on lai, hõlmates öko-füsioloogilisi, autökoloogilisi, dem-ökoloogilisi ja sün-ökoloogilisi aspekte. Tööde laia temaatilist ulatust arvestades on dissertatsiooni sünteesiv osa koostatud erinevaid uurimusi ühendava ülevaateartikli vormis, millesse üksikartiklite tulemused on lõimitud viidete abil. Töö selline ülesehitus vähendab artiklites esitatu asjatut kordamist ning võimaldab käsitletavast teemast anda oluliselt laiema ja terviklikuma ülevaate, kattes ka neid aspekte, mida töö aluseks olevad artiklid otseselt ei käsitle. Järves valitsevaid tingimusi võib tinglikult jagada kolme suurte rühma – füüsikalised, keemilised ja bioloogilised, mis mõjutavad veetaimestikku limnoloogiliselt, metaboolselt ning biootiliselt. Järve limnoloogiline mõju avaldub läbi vee ja setete füüsikaliste parameetrite, vee liikumise, valgustingimuste ja temperatuuri. Metaboolne mõju on seotud toiteainete ringetega ja orgaanilise aine produktsiooniga ning biootiline mõju on seotud mitmesuguste veekogu organismirühmade ja veetaimestiku vaheliste suhete ning koosluste struktuuriga. Nimetatud tegurite rühmad moodustavad keeruka kompleksi, mille mõju avaldumist veetaimestikule on ülevaates käsitletud nii ajalises kui ruumilises skaalas. Veetaimede tundlikkusel veekogudes valitsevate tingimuste suhtes põhineb nende indikaatorväärtus, mis annab veetaimestiku uuringutele olulise rakendusliku aspekti, võimaldades taimekoosluste järgi hinnata veekogu seisundit ja selles toimuvaid muutusi. Tehtud uuringute ühe peamise tulemustena selgitati välja Võrtsjärve taimekoosluste jaotumist ja struktuuri mõjutav tegurite kompleks, milles juhtival kohal on toiteainete kättesaadavus ja valitsevate tuulte mõju, mis Võrtsjärve spetsiifilise kuju tõttu tekitavad taimestiku omapärase polariseerumise nii põhja-lõuna kui ida-lääne suunas. Võrdlus 20. sajandi algusest pärinevate ajalooliste andmetega näitas, et Võrtsjärve veetaimestiku liigiline koosseis on kõigist elustikurühmadest kõige enam muutunud. Muutuste peamiseks põhjuseks on eutrofeerumine jõgede kaudu järve jõudvate toiteainete mõjul. Viimase 20 aasta satelliidifotodelt nähtub, et muutused jätkuvad, mille üheks ilminguks on roostike kiire laienemine keskmise kiirusega 2.2 m aastas, mis on eriti markantne jõesuudmete ümbruses. Suurtaimede produktsioon moodustas Võrtsjärves 35,5% järve suvisest koguproduktsioonist, sügavamas Peipsis, kus litoraali osakaal järve kogupindalas on väiksem, oli see näitaja 10%. Kahe Vooremaa järve uuringud selgitasid, kuidas järve suurusega kasvav tuule mõju aitab kaasa tasakaalu nihkumisele suurtaimede valitsemiselt fütoplanktoni valitsemisele ja kuidas sel moel kujunevad erinevad valgustingimused muudavad taimede arhitektuuri.Järve ökosüsteemis on veetaimestikul väga oluline roll, mida võib tinglikult jagada aktiivseks, kus veetaimed mõjutavad järves toimuvaid protsesse ja kujundavad elutingimusi teistele järve asukatele ning passiivseks, kus veetaimed on ise mõjutatud järves toimuvatest protsessidest. Väikestes ja madalates järvedes, kus taimedega asustatud litoraal moodustab suure osa järve kogupindalast, on ülekaalus taimede aktiivne funktsioon nii toidu tootja, varje pakkuja kui elupaiga loojana, kuid enamasti see ülekaal kahaneb nii järve pindala ja sügavuse kasvades ning suurtes järvedes on taimestik enam allutatud ilmastikust ja järvenõo kujust sõltuvatele teguritele. Kuna suurem osa järvi maailmas on väikese pindalaga ning madalad, on suurem rõhuasetus veekogude taimestiku uuringutes langenud veetaimestiku aktiivse rolli selgitamisele veekogus. Käesolev töö keskendub vastupidisele aspektile – küsimustele, kuidas mõjutavad järves valitsevad tingimused taimeliikide levikut, nende morfomeetrilisi näitajaid ja taimekoosluste struktuuri ja kuidas neid näitajaid saab kasutada järves valitsevate tingimuste hindamisel. Käesoleva töö materjal on kogutud 14 aasta jooksul kokku üheksast Eesti järvest, kuid peamine andmestik pärineb Võrtsjärvest ja kahest Vooremaa järvest, Prossast ja Kaiaverest. Töös kirjeldatud teemade ring on lai, hõlmates öko-füsioloogilisi, autökoloogilisi, dem-ökoloogilisi ja sün-ökoloogilisi aspekte. Tööde laia temaatilist ulatust arvestades on dissertatsiooni sünteesiv osa koostatud erinevaid uurimusi ühendava ülevaateartikli vormis, millesse üksikartiklite tulemused on lõimitud viidete abil. Töö selline ülesehitus vähendab artiklites esitatu asjatut kordamist ning võimaldab käsitletavast teemast anda oluliselt laiema ja terviklikuma ülevaate, kattes ka neid aspekte, mida töö aluseks olevad artiklid otseselt ei käsitle. Järves valitsevaid tingimusi võib tinglikult jagada kolme suurte rühma – füüsikalised, keemilised ja bioloogilised, mis mõjutavad veetaimestikku limnoloogiliselt, metaboolselt ning biootiliselt. Järve limnoloogiline mõju avaldub läbi vee ja setete füüsikaliste parameetrite, vee liikumise, valgustingimuste ja temperatuuri. Metaboolne mõju on seotud toiteainete ringetega ja orgaanilise aine produktsiooniga ning biootiline mõju on seotud mitmesuguste veekogu organismirühmade ja veetaimestiku vaheliste suhete ning koosluste struktuuriga. Nimetatud tegurite rühmad moodustavad keeruka kompleksi, mille mõju avaldumist veetaimestikule on ülevaates käsitletud nii ajalises kui ruumilises skaalas. Veetaimede tundlikkusel veekogudes valitsevate tingimuste suhtes põhineb nende indikaatorväärtus, mis annab veetaimestiku uuringutele olulise rakendusliku aspekti, võimaldades taimekoosluste järgi hinnata veekogu seisundit ja selles toimuvaid muutusi. Tehtud uuringute ühe peamise tulemustena selgitati välja Võrtsjärve taimekoosluste jaotumist ja struktuuri mõjutav tegurite kompleks, milles juhtival kohal on toiteainete kättesaadavus ja valitsevate tuulte mõju, mis Võrtsjärve spetsiifilise kuju tõttu tekitavad taimestiku omapärase polariseerumise nii põhja-lõuna kui ida-lääne suunas. Võrdlus 20. sajandi algusest pärinevate ajalooliste andmetega näitas, et Võrtsjärve veetaimestiku liigiline koosseis on kõigist elustikurühmadest kõige enam muutunud. Muutuste peamiseks põhjuseks on eutrofeerumine jõgede kaudu järve jõudvate toiteainete mõjul. Viimase 20 aasta satelliidifotodelt nähtub, et muutused jätkuvad, mille üheks ilminguks on roostike kiire laienemine keskmise kiirusega 2.2 m aastas, mis on eriti markantne jõesuudmete ümbruses. Suurtaimede produktsioon moodustas Võrtsjärves 35,5% järve suvisest koguproduktsioonist, sügavamas Peipsis, kus litoraali osakaal järve kogupindalas on väiksem, oli see näitaja 10%. Kahe Vooremaa järve uuringud selgitasid, kuidas järve suurusega kasvav tuule mõju aitab kaasa tasakaalu nihkumisele suurtaimede valitsemiselt fütoplanktoni valitsemisele ja kuidas sel moel kujunevad erinevad valgustingimused muudavad taimede arhitektuuri

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”)

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

A Future Tale of Two Winters? Sediment-water interface nitrogen dynamics in Lake Võrtsjärv (Estonia) during the ice-free winter 2019/2020 : [presentation]

The presentation took place at the Lahti Lakes 2021 Symposium.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 95196. Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 95196. Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”

Puntos de inflexión en los gradientes de composición de las comunidades de plantas acuáticas de diferentes continentes

Unravelling patterns and mechanisms of biogeographical transitions is crucial if we are to understand compositional gradients at large spatial extents, but no studies have thus far examined breakpoints in community composition of freshwater plants across continents. Using a dataset of almost 500 observations of lake plant community composition from six continents, we examined, for the first time, if such breakpoints in geographical space exist for freshwater plants and how well a suite of ecological factors (including climatic and local environmental variables) can explain transitions in community composition from the subtropics to the poles. Our combination of multivariate regression tree (MRT) analysis and k-means partitioning suggests that the most abrupt breakpoint exists between temperate to boreal regions on the one hand and freshwater plant communities harbouring mainly subtropical or Mediterranean assemblages on the other. The spatially structured variation in current climatic conditions is the most likely candidate for controlling these latitudinal patterns, although one cannot rule out joint effects of eco-evolutionary constraints in the harsher high-latitude environments and post-glacial migration lags after Pleistocene Ice Ages. Overall, our study supports the foundations of global regionalisation for freshwater plants and anticipates further biogeographical research on freshwater plant communities once datasets have been harmonised for conducting large-scale spatial analyses.publishedVersio

Puntos de inflexión en los gradientes de composición de las comunidades de plantas acuáticas de diferentes continentes

Sección: SIBECOL-AIL Meeting in Aveiro-2022[EN] Unravelling patterns and mechanisms of biogeographical transitions is crucial if we are to understand compositional gradients at large spatial extents, but no studies have thus far examined breakpoints in community composition of freshwater plants across continents. Using a dataset of almost 500 observations of lake plant community composition from six continents, we examined, for the first time, if such breakpoints in geographical space exist for freshwater plants and how well a suite of ecological factors (including climatic and local environmental variables) can explain transitions in community composition from the subtropics to the poles. Our combination of multivariate regression tree (MRT) analysis and k-means partitioning suggests that the most abrupt breakpoint exists between temperate to boreal regions on the one hand and freshwater plant communities harbouring mainly subtropical or Mediterranean assemblages on the other. The spatially structured variation in current climatic conditions is the most likely candidate for controlling these latitudinal patterns, although one cannot rule out joint effects of eco-evolutionary constraints in the harsher high-latitude environments and post-glacial migration lags after Pleistocene Ice Ages. Overall, our study supports the foundations of global regionalisation for freshwater plants and anticipates further biogeographical research on freshwater plant communities once datasets have been harmonised for conducting large-scale spatial analyses[ES] Desentrañar los patrones y mecanismos que subyacen a las transiciones biogeográficas es un requisito fundamental a la hora de comprender los gradientes de composición de las comunidades ecológicas a grandes extensiones espaciales, si bien ningún estudio ha examinado explícitamente estos puntos de inflexión para comunidades de plantas acuáticas de diferentes continentes. Utilizando una completa base de datos que condensa un total de casi 500 observaciones individuales sobre las comunidades florísticas lacustres de seis continentes, este trabajo pretende delinear las transiciones biogeográficas en plantas acuáticas a escala global, así como valorar el papel que desempeñan diversos mecanismos ecológicos (a saber, las condiciones climáticas y las características locales del hábitat) sobre estos puntos de inflexión en el espacio geográfico comprendido entre las latitudes subtropicales y los polos. Nuestros resultados obtenidos mediante la ejecución simultánea de árboles de regresión multivariante (MRT) y algoritmos de agrupación por k-medias demuestran la existencia de un punto de inflexión entre las regiones templadas y boreales y los lagos localizados en las bandas subtropicales y en las inmediaciones del Mediterráneo. La estructura espacial que subyace a la distribución de los condicionantes climáticos en nuestro planeta parece ser el principal mecanismo de control de dichas transiciones biogeográficas, si bien estos patrones latitudinales también podrían explicarse en base a constricciones eco-evolutivas en las regiones más septentrionales y a la colonización diferencial de los territorios norteños antaño cubiertos por el hielo durante el Último Máximo Glacial. En síntesis, nuestro estudio proporciona una base teórica preliminar para futuras investigaciones encaminadas a delimitar las unidades geográficas de los principales componentes de la flora acuática contemporánea y también anticipa un creciente interés por los estudios de carácter fitogeográfico en las aguas continentales, si bien los análisis venideros deberán prestar especial atención a la armonización de datos biológicos potencialmente heterogéneos en naturaleza y con orígenes disparesSIJGG was funded by the European Union Next Generation EU/PRTR (grant no. AG325). Academy of Finland supported JH, JGG (grant no. 331957), and JA (grant no. 322652). CFL appreciates financial support from the Spanish Ministry of Science and Technology (grant no. CL2017- 84176R). BAL was supported by National Research, Development, and Innovation Office (grant no. NKFIH, OTKA FK127939) and by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences. SK was supportedby NWO Vidi (grant no. 203098). LR was funded by MESRSI (Ministry of Higher Education, Scientific Research and Innovation of Morocco) as part of the BiodivRestore Program (RESPOND Project) and by the Tour du Valat Foundation. Sampling of the Brazilian coastal lakes was financed by NWO (grant no. W84-549), the National Geographic Society (grant no. 7864-5), and CNPq (grants no. 480122, 490409, 311427

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.Peer reviewe

Black and white, day and night – fish diurnal movements in two different Amazonian lakes : [presentation] 

The presentation took place at the 10th International Conference on Shallow Lakes in 2021.This work was supported by the Estonian Research Council grant PRG705 and EMU P190258. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963.This work was supported by the Estonian Research Council grant PRG705 and EMU P190258. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963

The comparison of the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of northern temperate lakes

We studied the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of four different lakes – one Latvian (Auciema) and three Estonian (Akste, Kaiavere, and Prossa). Altogether, 162 perch larvae (81 from both habitats) were collected to estimate the diet composition of gathered larval specimens in spring (2019) using gut content analysis via epifluorescence microscopy. Attention was paid particularly to the question how does the larval perch food composition differ in pelagic and littoral habitats. We hypothesized that the consumption of zooplankton is higher and the larval condition is better in littoral habitats. We assessed the feeding on both protozoo- (ciliates) and metazooplankton and applied multiple indices (Hurlbert’s standardized niche breadth, Ivlev’s selectivity and relative importance index) to evaluate, respectively, the larval fish prey importance, feeding homogeneity and strategies. The results showed that larval length and weight were slightly higher and body condition was slightly better in the lakes’ littoral habitats. The feeding niche of perch larvae was narrower in the littoral, which can indicate more favourable feeding conditions in littoral than lake pelagic habitats. While the small cladocerans (Bosmina longirostris Müller) were generally the preferred and important food objects, ciliates were avoided and consumed only when their share in the total zooplankton biomass was >40%. However, in shortage of cladocerans, ciliates could be vitally important food objects for perch larvae.This project has received funding from the European Union’s Horizon 2020 research and innovation pro- gramme under grant agreement No. 951963. The research is part of the project “Fish feeding conditions in lakes with different planktonic food web structure and mac- rovegetation” (MICROFISH), No. 1.1.1.2/VIAA/1/18/301, in agreement with State Education Development Agency of the Republic of Latvia Programme No. 1.1.1.2/16/I/001. 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. We would like to thank Jukka Ruuhijärvi and an anonymous reviewer for their helpful comments on the earlier version of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences.This project has received funding from the European Union’s Horizon 2020 research and innovation pro- gramme under grant agreement No. 951963. The research is part of the project “Fish feeding conditions in lakes with different planktonic food web structure and mac- rovegetation” (MICROFISH), No. 1.1.1.2/VIAA/1/18/301, in agreement with State Education Development Agency of the Republic of Latvia Programme No. 1.1.1.2/16/I/001. 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. We would like to thank Jukka Ruuhijärvi and an anonymous reviewer for their helpful comments on the earlier version of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences