The northern landscapes are warming twice as fast as the Earth’s average because of climate change. This impacts lake ecosystem functions. Researchers have noticed changes in lake food webs.
In many northern lakes, higher temperatures is associated with increases in water color (“browning”) and nutrients (“eutrophication”) which, altogether, have potential negative impacts on lake ecosystem functions. One of the functions most likely affected is the provisioning of essential, polyunsaturated fatty acids (PUFA) that are key for fish growth and considered an indicator of food quality. As an important link between phytoplankton and fish, zooplankton play a main role in making these PUFA available to fish on the top of lake food webs, and ultimately to human consumption.
In a recent article published in Limnology and Oceanography, researchers from the Swedish University of Agricultural Sciences (SLU) and from the Institut National de la Recherche Scientifique (INRS) found that the effects of climate change on PUFA supplies differed drastically between two widespread groups of crustacean zooplankton. Cladocerans, commonly known as “water fleas”, reduced 10 times their PUFA levels with increasing temperature, water color and nutrients, whereas the shrimp-like copepods maintained high levels of PUFAs under the same changes associated with climate change.
The main environmental driver for changes in zooplankton fatty acid composition also differed between the two groups, with cladocerans mainly responding to temperature and copepods to water color.
Changes in zooplankton quality combined with zooplankton community shifts toward dominance by cladocerans in warmer, browner, and more nutrient-rich conditions would mean an overall reduction in PUFA supply from zooplankton for fish, thus having a strong potential to affect fish production and well-being, says researcher Fernando Chaguaceda.
Another novel finding of this study was that lake size moderated the negative effects of climate change on zooplankton PUFA, as larger lakes had higher abundances of PUFA-rich phytoplankton groups that are suitable food for zooplankton. These results suggests the important role of large lakes in alleviating the negative effects of climate change on zooplankton quality, while the impact of climate change in smaller lakes is likely to be strongest.
The authors call for future efforts in understanding and mitigating the effects of climate change on zooplankton quality focusing on smaller lakes, which appear to be most susceptible to climate change. This is particularly important as small lakes (smaller than 1km2) are the most abundant, and represent more than 40% of the lake surface in the world.
Zooplankton sampling in Guoledisjávrre in August 2021. Gillaume and Liesbeth are casting funnel-shaped plankton nets, which they will retrieve to capture and concentrate the zooplankton suspended in the lake water column. Photo by Fernando Chaguaceda.
1/1
Chaguaceda, F., D. C. P. Lau, W. Goedkoop, M. Fadhlaoui, I. Lavoie, and T. Vrede. 2024. Zooplankton in northern lakes show taxon-specific responses in fatty acids across climate-productivity and ecosystem size gradients. Limnology and Oceanography n/a. doi:10.1002/lno.12539