title: Terrestrial carbohydrates support freshwater zooplankton during phytoplankton deficiency.
abstract: Freshwater food webs can be partly supported by terrestrial primary production, often deriving from plant litter of surrounding catchment vegetation. Although consisting mainly of poorly bioavailable lignin, with low protein and lipid content, the carbohydrates from fallen tree leaves and shoreline vegetation may be utilized by aquatic consumers. Here we show that during phytoplankton deficiency, zooplankton (Daphnia magna) can benefit from terrestrial particulate organic matter by using terrestrial-origin carbohydrates for energy and sparing essential fatty acids and amino acids for somatic growth and reproduction. Assimilated terrestrial-origin fatty acids from shoreline reed particles exceeded available diet, indicating that Daphnia may convert a part of their dietary carbohydrates to saturated fatty acids. This conversion was not observed with birch leaf diets, which had lower carbohydrate content. Subsequent analysis of 21 boreal and subarctic lakes showed that diet of herbivorous zooplankton is mainly based on high-quality phytoplankton rich in essential polyunsaturated fatty acids. The proportion of low-quality diets (bacteria and terrestrial particulate organic matter) was <28% of the assimilated carbon. Taken collectively, the incorporation of terrestrial carbon into zooplankton was not directly related to the concentration of terrestrial organic matter in experiments or lakes, but rather to the low availability of phytoplankton.
authors: Lammi Biological Station, University of Helsinki, Pääjärventie 320, FIN-16900 Lammi, Finland.|Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland.
authors: Sami J
authors: SJ
authors: Taipale
authors: Oregon Institute of Marine Biology, University of Oregon, P.O. Box 5389, Charleston, Oregon, USA.
authors: Aaron W E
authors: AW
authors: Galloway
authors: Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35 (YA), 40014 Jyväskylä, Finland.
authors: Sanni L
authors: SL
authors: Aalto
authors: Kilpisjärvi Biological Station, University of Helsinki, Käsivarrentie 14622, FIN-99490 Kilpisjärvi, Finland.|Department of Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 University of Helsinki, Finland.
authors: Kimmo K
authors: KK
authors: Kahilainen
authors: Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland.
authors: Ursula
authors: U
authors: Strandberg
authors: Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland.
authors: Paula
authors: P
authors: Kankaala
mesh_terms: D000818:Animals; D050260:Carbohydrate Metabolism; D002241:Carbohydrates; D003621:Daphnia / Q000502:physiology*; D005227:Fatty Acids / Q000032:analysis; D020387:Food Chain; D005618:Fresh Water / Q000737:chemistry*; D060106:Lakes / Q000737:chemistry; D015048:Zooplankton / Q000502:physiology*
chemical_list: D002241:Carbohydrates; D005227:Fatty Acids