Poor nutritional quality of primary producers and zooplankton driven by eutrophication is mitigated at upper trophic levels

Abstract

Eutrophication and rising water temperature in freshwaters may increase the total production of a lake while simultaneously reducing the nutritional quality of food web components. We evaluated how cyanobacteria blooms, driven by agricultural eutrophication (in eutrophic Lake Köyliöjärvi) or global warming (in mesotrophic Lake Pyhäjärvi), influence the biomass and structure of phytoplankton, zooplankton, and fish communities. In terms of the nutritional value of food web components, we evaluated changes in the ω‐3 and ω‐6 polyunsaturated fatty acids (PUFA) of phytoplankton and consumers at different trophic levels. Meanwhile, the lakes did not differ in their biomasses of phytoplankton, zooplankton, and fish communities, lake trophic status greatly influenced the community structures. The eutrophic lake, with agricultural eutrophication, had cyanobacteria bloom throughout the summer months whereas cyanobacteria were abundant only occasionally in the mesotrophic lake, mainly in early summer. Phytoplankton community differences at genus level resulted in higher arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) content of seston in the mesotrophic than in the eutrophic lake. This was also reflected in the EPA and DHA content of herbivorous zooplankton (Daphnia and Bosmina) despite more efficient trophic retention of these biomolecules in a eutrophic lake than in the mesotrophic lake zooplankton. Planktivorous juvenile fish (perch and roach) in a eutrophic lake overcame the lower availability of DHA in their prey by more efficient trophic retention and biosynthesis from the precursors. However, the most efficient trophic retention of DHA was found with benthivorous perch which prey contained only a low amount of DHA. Long‐term cyanobacterial blooming decreased the nutritional quality of piscivorous perch; however, the difference was much less than previously anticipated. Our result shows that long‐term cyanobacteria blooming impacts the structure of plankton and fish communities and lowers the nutritional quality of seston and zooplankton, which, however, is mitigated at upper trophic levels.

Autochthonous production sustains food webs in large perialpine lakes, independent of trophic status: Evidence from amino acid stable isotopes

“…While our study focuses on the general pattern of primary production in perialpine lakes, eutrophication could affect the OC cycling in many other ways: food quality (Taipale et al, 2022), energy transfer efficiency (Mehner et al, 2022), biodiversity (Glibert, 2017; Watson et al, 1997) or food web structure and resilience (Kelly & Schallenberg, 2019). The stable isotope analysis of specific compounds, such as AAs, also opens new ways to answer some of these questions.…”

Sustainable lake restoration: From challenges to solutions

“…Increasing catch proportions have ended up in food production, thus providing a link to the transition to a "blue" bioeconomy and implementation of the EU's Farm to Fork Strategy. Although cyprinids are not usually targeted in commercial and recreational fishing, they offer quality protein and fatty acids for human consumption (Taipale et al, 2022). The estimated ecologically sustainable catch potential for roach is around 19 million kg year À1 in Finnish inland waters, and implementation of commercial biomanipulation is now planned for several lakes (Ruokonen et al, 2019).…”

The importance of omega‐3 polyunsaturated fatty acids as high‐quality food in freshwater ecosystems with implications of global change

“…For planktivorous bighead carp ( Hypophthalmichthys nobilis ), EPA content also decreased with the reduction in abundance of high‐quality phytoplankton during eutrophication (Razavi et al ., 2014). By contrast, the cyprinids Rutilus rutilus and Abramis brama , were more adaptable to variations in high‐quality food sources during eutrophication, and their biomass increased significantly, accounting for about 66% of the total fish biomass in the eutrophic lakes (Taipale et al ., 2022 b ).…”

“…Eutrophication (Müller‐Navarra et al ., 2004), rising temperatures (Guschina & Harwood, 2009; Hixson & Arts, 2016; Lau et al ., 2021), removal of riparian vegetation leading to increased light intensity (Guo et al ., 2015, 2016 d ), heavy metal pollution (Chia, Lombardi & Gama Melão, 2013 a ), and increases in salinity (Kopprio et al ., 2018) are reported to reduce the ω3‐PUFA content and thus the nutritional quality of food sources. Declining availability of high‐quality food sources undoubtedly has negative effects on freshwater consumers (Müller‐Navarra et al ., 2004; Brucet et al ., 2013; Taipale et al ., 2019 a , b , 2022 b ), and also causes nutritional phenological mismatches between terrestrial consumers and aquatic insects (Shipley et al ., 2022). However, it remains unclear how global environmental change affects the sources and fate of high‐quality food within and across ecosystems.…”