Finalized fieldwork campaigns for improved knowledge on Latvian and Estonian lake food webs


Researchers and Estonian post-doctorate Katrit Karus from Institute for Environmental Solutions (IES) finalized fieldwork campaigns that will improve knowledge on function of food webs in Latvian and Estonian lakes.

Researchers carried out studies in 8 lakes (4 in Latvia and 4 in Estonia). It included 3 fieldwork campaigns with the intention to determine how whole planktonic community structure and aquatic plants in lakes influence the development of natural fish resources – stock development, survival and their eating habits. Planktonic community organisms in lakes are studied as potential food items for fish larvae. Ability to encounter and intercept food items is critical for their survival of fish larvae. Aquatic plants are studied as the living environment and shelter for planktonic communities and fish communities.

Fieldworks lasted altogether 20 days during spring, summer and autumn in 2019. The study lakes were selected to be located in different areas of Latvia and Estonia, as well as highly variable in lake types macrophyte and fish community indices.

Lake name

National lake type (EE/LV)

Surface area (ha)


depth (m)


depth (m)

Kaiavere järv

Type 2 (EE): shallow lake with medium water hardness




Riebinu ezers

Type 5 (LV): shallow clearwater lake with high water hardness




Nohipalo Valgejärv

Type 5 (EE): softwater light coloured lake





Type 5 (LV): shallow clearwater lake with high water hardness




Prossa järv

Type 2 (EE): shallow lake with medium water hardness




Auciema ezers

Type 2 (LV): very shallow brown-water lake with high water hardness




Akste järv

Type 4 (EE): softwater brown coloured lake



Vārzgūnes ezers

Type 4 (LV): very shallow brown water lake with low water hardness




Characteristic features of 8 study lakes throughout Latvia and Estonia.


To implement a holistic approach of lake research, the researchers conducted sampling of the following indicators:

Macrophyte community(as living places and shelter). Researchers decided to implement macrophyte community  studies 3 times this year instead of 2 times (spring, summer) as initially planned, because of quite big seasonal changes in their community structure. For macrophyte community studies researchers used a transect method in a combination of sampling quadrates (1x1m, 2x2m) that makes possible to understand how macrophytes are structuring the relationships between planktonic communities and fish. Altogether, 49 transects were studied per each season in selected lakes. Moreover, during all 3 sampling seasons 1072 sampling quadrates were studied in selected lakes.

Fish communities. Researchers used Nordic gillnets for fish community studies. Samples were collected from costal and open-water areas of the Estonian lakes in summer 2019. Altogether, researchers caught and analysed 1961 fish individuals from all the lakes. Each fish were identified, measured (total length) and weighed and all the data were compiled. In 2019 only fish communities in Estonian lakes were studied, in case of Latvian lakes it is planned to use the data collected in summer 2018.

Larval fish. Larval fish samples were collected using bongonets and scoopnets from costal and pelagial areas of the lakes. During collected individual analysis their diet will be assesed. To study and collect young fish (0+ fish) communities beach-seine method was used successfully in all the 8 study lakes both in summer and autumn. Altogether, 1842 fish were collected in summer from all the study lakes. All the young fish individuals are identified, measured (total length) and weighed.

Plankton samples. Alltogether, 240 plankton (including bacteria, phytoplankton, ciliates, heterotrophic nanoflagellates, metazooplankton, 48 samples per planktonic group) samples were collected during fieldworks from costal (120 samples) and open-water areas (120 samples) of the lakes to analyse their community structure, abundance and biomass.

Physico-chemical parameters. In addition to the collection of planktonic samples, some physico-chemical parameters (transparency, colour, temperature, conductivity, pH, dissolved oxygen content, oxygen saturation, total phosphorus, total nitrogen) were also measured during the fieldworks, both from costal and open-water areas of the lakes. All the analyses (e.g. total phosphorus, total nitrogen) are already completed also in the laboratory. A dataset with physico-chemical data was compiled.

All the gathared samples and collected individuals will be analysed at the beginning of 2020 to continue research on fish feeding conditions in lakes with different planktonic food web structure and macrovegetation.

Post-doctorate Karus also took part from a seminar with oral presentation to introduce her post-doctoral project to doctoral students and their supervisors from Estonian University of Life Sciences. The action was organized by collaboration of Institute for Environmental Solutions and Estonian University of Life Sciences. It was supported by the European Union, European Regional Development Fund (Estonian University of Life Sciences ASTRA project „Value-chain based bio-economy“).

The research is part of the project „Fish feeding conditions in lakes with different planktonic food web structure and microvegetation “(MICROFISH), No. Agreement with State Education Development Agency of the Republic of Latvia No. Programme number 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”.

Find out more about the project here.