Fieldwork campaigns to improve knowledge on function of Latvian and Estonian lake food webs


Institute for Environmental Solutions (IES) in cooperation with Estonian post-doctorate Katrit Karus has implemented the first three fieldwork campaigns on Latvian and Estonian lakes. Complex study of lake food webs will emphasize the importance of larval fish community studies.


Researchers carried out studies in 8 lakes with the intention to determine how whole planktonic community structure (all planktonic organisms as potential food items for fish larvae) and aquatic plants in lakes (as the living environment for fish) influence the development of natural fish resources – fish stock development, fish survival and their eating habits. Post-doctorate K.Karus chose 8 study lakes – 4 in Latvia (Riebinu, Auciema, Laukezers, Varzgune) and 4 in Estonia (Akste, Nohipalo Valgjärv, Kaiavere, Prossa) locating throughout both countries. From 4 field works that were planned this year – preliminary fieldwork and 3 real fieldwork campaigns in spring, summer and autumn post-doctorate has already finished first 3 parts. Preliminary fieldworks were done in spring to check the potential study lakes and to decide which ones are most suitable. During this process researchers carried out fish community studies in Lake Akste and Meelva to get an initial information about fish community structure in the lakes.

Spring fieldwork campaign in Latvian lakes took place in beginning of May and beginning of June on Estonian lakes. For characterization purpose researchers carried out physico-chemical measurements in all the studied lakes. In result data about water transparency, temperature, dissolved oxygen content, oxygen saturation, conductivity, pH, and content of total phosphorus and total nitrogen (together 16 total phosphorus and 16 total nitrogen samples per sampling season) were achieved from these measurements.

For biological parameters, bacterio-, phyto-, protozoo- (ciliate and heterotrophic nanoflagellate samples) and metazooplankton samples were collected from littoral and open-water areas of the lakes. Altogether 10 planktonic samples (2 samples per planktonic group) were collected from one lake per season. Macrophyte community studies were carried out in all the lakes using a transect method in a combination of sampling quadrates to study how macrophytes (as living places and shelter) are structuring the relationships between planktonic communities and fish. Young fish community (0+ fish) was studied by standard (bongonets) and novel (flying camera drone) fieldwork methodology and equipment for checking the possibility to use bongonets and flying camera drones to study larval fish communities and assess their abundances and fianlly to compare these two methods for assessing larval fish abundances. At least 20 larvae from each lake were collected to assess their diet via novel gut segmentation analysis to test if there is enough food for newly hatched fish larvae.

Summer fieldwork campaign took place in the beginning of July on Latvian lakes and in the end of July on Estonian lakes. Physico-chemical measurements and planktonic sampling was carried out similarly with spring field work campaign. Alltogehter 10 planktonic (bacterio-, phyto-, protozoo- (ciliates, heterotrophic nanoflagellates), metazooplankton) samples, 2 samples per planktonic group, were collected from a lake. Fish community studies were carried out using several floating and bottomset Nordic gillnets (number of gillnets was lake specific) to characterize lakes fish community structure. Young fish community was studied by beach-seines in all the study lakes. Young fish (0+ fish) were not able to study via Nordic gillnetting, no small fish were present in the gillnets. Macrophyte studies were carried out similarly as during spring campaign.

So far, autumn fieldwork campaign took place only in Estonian lakes in the middle of September. Fieldworks on Latvian lakes will take place in the end of September. Physico-chemical measurements, planktonic sampling and macrophyte studies were carried out similarly with spring and summer field work campaign. Young fish community studies were carried out again by using beach-seines from all the study lakes.

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.