MICROFISH project started on January 8th 2019 and will end on January 7th 2022. The project was carried out by 3 involved parties – the post-doctorate, the applicant organisation (Institute for Environmental Solutions, IES) and partner organisation (Estonian University of Life Sciences, EULS). The overall aim of the research project was to study how macrophytes as habitats and whole plankton communities (including microbial loop - microbial food web) act as a food source influencing fish feeding in different lakes.
Objectives of the project with planned results:
1. Overall aim of the research: to study how macrophytes as habitats and plankton communities (including microbial loop) as food sources influence fish feeding in different lakes.
Answer: Aim fulfilled. Our studies showed that studied eight lakes categorized into three different macrophyte ecological groups and all these groups had a strong influence on plankton communities. The zooplankton was dominant part of juvenile perch diet in all studied lakes. In our study lakes there was evident connection between the abundance of zooplankton and the amount of zooplankton consumed by juvenile fish. We found clear correlation between zooplankton biomass consumption in summer and the fish growth rate. In the other hand, the lowest growth rate was detected in L. Laukezers, where zooplankton consumption was also lowest.
Our main scientific questions (Q1-Q3) to clarify and hypotheses (H1-H3) to control were:
Question 1: How is fish year-class strength affected by the planktonic food web structure, especially by microbial loop?
Hypothesis 1: Balance between microbial loop and classical food chain determines the fish year-class strength.
Answer 1: Hypothesis accepted. Our results showed that the high spring proportion of protozoa in zooplankton has a favourable effect on 0+ fish growth. For example, we found in summer the largest perch fry in the lake with the highest proportion of ciliates in spring. However, if we look at the overall growth of 0+ fish, the highest growth rates were found in the lakes, where the proportion of ciliates in summer was the lowest. We detected negative correlation between the share of protozoans in the zooplankton in the summer and 0+ fish growth rates. Perfect balance between microbial loop and classical food chain, considering 0+ fish growth, seems to be high (>30%) amount of ciliates in zooplankton biomass in the spring, followed by their decline in (<20%) summer. The results are formulated as deliverables D.4.4.1 and D.4.4.3., and as scientific manuscripts MS1 and MS3.
Question 2: How do fish affect the structure of microbial loop?
Hypothesis 2: Fish feeding pressure determines microbial loop structure.
Answer 2: Hypothesis accepted. We found that the number of metazooplankters consumed by 0+ fish was in positive correlation with the biomass of heterotropic nanoflagellates (both in summer and autumn). The amount of metazooplankton biomass consumed was in positive correlation with ciliates biomass in summer. The number of metazooplankters consumed by 0+ perch had a positive impact in bacterivorous ciliates cell size in summer and negative impact in autumn. This indicates that metazooplankton exert a strong grazing pressure on large bacterivorous ciliates in summer and small bacterivores in autumn. This is most likely the effect of juvenile planktivorous fish, whose diet has reduced the size of the grazing metazooplankters. This assumption is also supported by the fact that the biomass of metazooplankton consumed by juvenile fish was negatively correlated with the biomass of bacterivorous ciliates in summer and positively in autumn. These results are formulated as deliverables D.4.4.1. and D.4.4.3, and as scientific manuscripts MS1 and MS3.
Question 3: How are macrophytes structuring the relationships between microbial loop and planktivorous fish?
Hypothesis 3: Macrophytes have a highly important role balancing the relationships between microbial loop and classical food chain.
Answer 3: Hypothesis accepted. Macrophytes had strong influence on planktonic food web components, but their influence did not cascade down to the level of heterotrophic bacteria and heterotrophic nanoflagellates. Our studies showed that studied eight lakes categorized into three different macrophyte ecological groups (lakes dominated by emergent, floating+floating-leaved or submerged vegetation) and all these groups had a strong influence on plankton communities (except heterotrophic bacterioplankton and nanoflagellates), 0+ fish and large fish. Different dominating macrophyte growth forms had different structural effects on food web components, which in turn create different top-down effects and modify the relationships between microbial loop and classical food chain. The results of macrophyte structuring abilities are formulated as a deliverable D2.6. and by a scientific manuscript D.4.4.2.
Achieved project outputs include:
Participation on three international scientific conferences, which all took place only in a virtual format due to the COVID-19 restrictions:
Submission of scientific manuscripts to a high-quality peer-reviewed scientific journals:
The Latvian and Estonian lake food web research is a part of the project „Fish feeding conditions in lakes with different planktonic food web structure and microvegetation “(MICROFISH), No.126.96.36.199/VIAA/1/18/301. Agreement with State Education Development Agency of the Republic of Latvia No. 188.8.131.52/16/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.