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Increasing Temperature Increases Algal, Fish Biomass in Northern Finland Lakes

Subarctic regions are experiencing quick changes not just in climate but also in land-use intensity. Recently, an international research group completed a study to observe how these changes are influencing the food webs and fish communities of lakes situated in northern Finland.

In northern lakes, algal and fish biomass are increasing with temperature and productivity. At the same time, fish communities are changing from whitefish towards roach dominance. Image Credit: Kimmo Kahilainen and Brian Hayden.

Biomasses and omega-3 fatty acids, EPA and DHA, were identified from the algal producers at the base of the food web to huge carnivorous fish from 20 lakes over a marked climatic and productivity gradient. Rising temperature and nutrient load shift food webs towards communities adapted to murky water.

The researchers quantified the amount of fish and invertebrates from 20 subarctic lakes with respect to climate and productivity gradient. They also determined the nutritional quality of organisms in every lake by quantifying useful omega-3 fatty acids, EPA, and DHA, from primary producer algae communities to top predators.

Scientists identified significant differences in the clear and murky water communities. With the increase in temperature and productivity, the biomass of algal and cyprinid fish communities was also found to increase.

Professor Kimmo Kahilainen from the Lammi Biological Station at the University of Helsinki organized this lake research program.

What we find in these food webs was community shift from clear water to murky lakes. We get a lot of fish from blue-green algal covered lakes, but there were no salmonid fishes anymore and the fish catch consisted almost exclusively of roach.

Kimmo Kahilainen, Professor, University of Helsinki

Changes in Fatty Acid Producing Algal Communities

Biomass present in lake food webs is mostly made of lipids, proteins, carbohydrates, and water. A portion of lipids is nutritionally very significant and includes essential omega-3 fatty acids, like EPA and DHA, which are effectively produced by a few algae, like diatoms in subarctic regions.

Invertebrates use up these algal basal producers and their EPA and DHA are shifted via the food web. Scientists quantified EPA and DHA content from the entire food web from algae to carnivorous fish in every lake.

Algal community changed from diatoms to blue-green algae and their quality decreased from clear to murky lakes, similar decreasing quality was also observed in invertebrates.

Mr Ossi Keva, Study Lead Author and PhD Student, University of Jyväskylä

Although there was a decrease in prey item quality, the proposed cascading impacts on fish were not noticed. Rather, an increase in the fish biomass in murky lakes resulted in increased total fatty acids.

Food webs in warmer and more productive environment do contain more fish and fatty acids, while the fish species itself shift from highly valued salmonids towards cyprinid dominated communities. Northern Finnish pristine subarctic lakes are not getting clearer in future, the change is more likely towards warmer and murky lakes modifying food web communities as well.

Mr Ossi Keva, Study Lead Author and PhD Student, University of Jyväskylä

Scientists from Finland, Canada, and Switzerland collaborated on the subarctic lake food web study.

Journal Reference:

Keva, O., et al. (2020) Increasing temperature and productivity change biomass, trophic pyramids and community-level omega-3 fatty acid content in subarctic lake food webs. Global Change Biology.


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