Improving the knowledge on food webs in Latvian and Estonian lakes

During the winter and spring seasons of 2020 Katrit Karus, the post-doctorate of the Institute for Environmental Solutions (IES) continues a comprehensive research on food webs in Latvian and Estonian lakes.

In this interview leading researcher Katrit Karus highlights the importance of this research and ongoing activities.

IES: Why is it important to research the whole food webs in lakes?

K.K.: Research studies that include whole food web components from bacteria to phytoplankton-zooplankton (as potential food items of fish larvae), macrophytes (aquatic plants as the living environment) and fish are rare. If we do not know how the whole food web function in lakes, we cannot predict the changes in lake (for example, caused by climate change) which will impact overall ecosystem and development of fish stock.

“I think that we are among the few researchers who are trying to study food webs in comprehensive manner.”

This will allow us to understand how food webs function, so we can describe the mechanisms that determine the mortality of larval fish in water bodies which is crucial for fish stock management (fish farming, aquaculture).

IES: How did you select the lakes to research?

K.K.: Till now food web studies are mostly carried out only in eutrophic (nutrient rich) lakes but how food webs will function in other types of the lakes is almost unknown. Therefore, we tried to choose and study very different lakes to cover the gaps. Moreover, we tried to represent diverse living environments that will show how species cope with different conditions. In ideal conditions, most of the species cope with their living environment very well but it is rarely common for lakes in Latvia and Estonia. In reality, species in lakes must survive in extreme living conditions.

IES: In which stage is the research now?

All the samples gathered during the fieldworks in 2019 are being analysed during the winter and spring season of 2020. We have analysed 48 bacterioplankton samples assessing their abundance and biomass. We carried out analyses of 48 heterotrophic nanoflaggellate samples under epifluorescence microscope to determine their abundance and biomass. We also analysed larval fish gut content, so we have information on what they have been eating during their very first life stages in spring. Fish community calculations are also finalized for each of the researched lakes. We have also compiled dataset and final calculations on Macrophyte community (frequency, abundance, percentage volume infested). But we still have a lot of analysis to continue.

IES: What are your conclusions about the research so far – how the food webs function in different lakes?

K.K. It was planned to finish all the sample analyses by the end of March 2020. However, because of the Emergency State in Latvia and Estonia this process will be extended. We are all quite curious about the results, but conclusions will be available when researchers will finish microscopic analyses and final dataset compilation. But just based on fieldworks done in 2019 we can say that when the environment in lake is extremely oligotrophic (with very low amount of nutrients) we cannot expect rich fish communities. For example, lake Nohipalo Valgjärv in Estonia – number of fish species were extremely low compared to the same species in more eutrophic lakes such as Lake Riebiņu in Latvia.

It’s also important to mention that food object presence in water is extremely vital for the time of fish larvae hatching. They just float in the water (cannot swim, sight is poor, and they are vulnerable against predators). If there are no suitable food objects, we cannot expect development of successful fish communities.

IES: Based on the results, in which stage of quality are the researched lakes in Latvia and Estonia?

K.K.: Lake Laukezers in Latvia and lake Nohipalo Valgjärv in Estonia are in very good condition.

“During the fieldwork campaigns in lake Laukezers the locals were very interested what we are doing and if we have a permission to study their national treasure. It was good to see that people still care.”

In my opinion, more eutrophic lakes (but still good eutrophic lakes) were lake Kaiavere, lake Riebinu, lake Auciema. However, lake Varzgune and lake Prossa were very different from other lakes. These lakes are totally over-grown by macrophytes, the shores of the lakes are swampy which makes it difficult to reach it. These and other signs (for example, filamentous algae or epiphytic algae attached to the plants) show poor condition of these lakes. But these conclusions are based only on macrophyte community evaluations other results will be available after conclusion of all the sample analyses.

IES: How is the overall situation of availability of data and information about lakes in Latvia and Estonia?

K.K.: Both countries has quite good background data about lakes and their main biotic groups. This information is available because of habitat inventories (“Inventory of the Protected Biotopes of European Union Importance”) done in Latvia and Estonia. But this research on lake food web function requires more specific information, for example, zooplankton hydrobiological monitoring that abovementioned general monitoring does not include.

IES: What are the next steps for this research?

K.K.: The next step after finishing all the sample analyses is to think about collected data and results in order to understand how food webs function in different lake types and how it impacts fish stock. The main objective of the research is to improve knowledge on how lake food webs function, thereby enabling the development of scientific and data-based plans for the management of lakes that combine economic and ecological criteria.

The research is part of the project „Fish feeding conditions in lakes with different planktonic food web structure and microvegetation “(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 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.