Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption.
Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mgHUFAg-1) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r=0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r=0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r=0.74) and chrysophytes (r=0.70). Accordingly, the EPA+DHA content of perch muscle decreased with increasing total phosphorus (r2=0.80) and dissolved organic carbon concentration (r2=0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers.
Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland; Lammi Biological Station, University of Helsinki, Pääjärventie 320, 16900 Lammi, Finland; Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35 (YA), 40014 Jyväskylä, Finland. Electronic address: samit@u.washington.edu.
S J
SJ
Taipale
Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35 (YA), 40014 Jyväskylä, Finland; Finnish Environment Institute (SYKE), P.O. Box 140, FI-00251 Helsinki, Finland.
K
K
Vuorio
Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland.
U
U
Strandberg
Kilpisjärvi Biological Station, University of Helsinki, Käsivarrentie 14622, 99490 Kilpisjärvi, Finland; Department of Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 University of Helsinki, Finland.
K K
KK
Kahilainen
Finnish Environment Institute (SYKE), Jyväskylä Office, Survontie 9A, FI-40500, Finland.
M
M
Järvinen
Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland.
M
M
Hiltunen
Lammi Biological Station, University of Helsinki, Pääjärventie 320, 16900 Lammi, Finland; Department of Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 University of Helsinki, Finland.
E
E
Peltomaa
Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland.
P
P
Kankaala
D000818:Animals; D018533:Biomass; D004281:Docosahexaenoic Acids / Q000032:analysis* / Q000378:metabolism; D015118:Eicosapentaenoic Acid / Q000032:analysis* / Q000378:metabolism; D005068:Eutrophication; D005227:Fatty Acids; D005228:Fatty Acids, Essential; D005231:Fatty Acids, Unsaturated; D005399:Fishes; D020387:Food Chain; D006801:Humans; D060106:Lakes; D010471:Perches / Q000378:metabolism*; D010758:Phosphorus; D010839:Phytoplankton / Q000378:metabolism*
D005227:Fatty Acids; D005228:Fatty Acids, Essential; D005231:Fatty Acids, Unsaturated; D004281:Docosahexaenoic Acids; D010758:Phosphorus; D015118:Eicosapentaenoic Acid
Aquatic food webs; DHA; DOC; EPA; Environmental change; Human nutrition; Perch; Phosphorus; Phytoplankton