title: Dual fuels: intra-annual variation in the relative importance of benthic and pelagic resources to maintenance, growth and reproduction in a generalist salmonid fish.
abstract: Ecological systems are often characterized as stable entities. However, basal productivity in most ecosystems varies between seasons, particularly in subarctic and polar areas. How this variability affects higher trophic levels or entire food webs remains largely unknown, especially in these high-latitude regions. We undertook a year-long study of benthic (macroinvertebrate) and pelagic (zooplankton) resource availability, along with short (day/days: stomach content)-, medium (month: liver δ(13)C and δ(15)N isotopes)- and long-term (season: muscle δ(13)C and δ(15)N isotopes) assessments of resource use by a generalist fish, the European whitefish, in a deep, oligotrophic, subarctic lake in northern Europe. Due to the long ice-covered winter period, we expected to find general benthic reliance throughout the year, but also a seasonal importance of zooplankton to the diet, somatic growth and gonadal development of whitefish. Benthic and pelagic resource availability varied between seasons: peak littoral benthic macroinvertebrate density occurred in mid-winter, whereas maximum zooplankton density was observed in summer. Whitefish stomach content revealed a reliance on benthic prey items during winter and pelagic prey in summer. A seasonal shift from benthic to pelagic prey was evident in liver isotope ratios, but muscle isotope ratios indicated a year-round reliance on benthic macroinvertebrates. Whitefish activity levels as well as somatic and gonadal growth all peaked during the summer, coinciding with the zooplankton peak and the warmest water temperature. Stable isotopes of muscle consistently depicted the most important resource, benthic macroinvertebrates, whereas short-term indicators, that is, diet and stable isotopes of liver, revealed the seasonal significance of pelagic zooplankton for somatic growth and gonad development. Seasonal variability in resource availability strongly influences consumer growth and reproduction and may also be important in other ecosystems facing pronounced annual weather fluctuations.
authors.affiliation: Kilpisjärvi Biological Station, University of Helsinki, Käsivarrentie 14622, FI-99490, Kilpisjärvi, Finland.|Department of Environmental Sciences, University of Helsinki, PO Box 65, FI-00014, Helsinki, Finland.
authors.forename: Brian
authors.initials: B
authors.lastname: Hayden
authors.affiliation: Department of Ecological Genetics, Max Planck Institute for Limnology, D-24302, Plön, Germany.|School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.|Instituto de Ciencias Naturales Alexander Von Humboldt, Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile.
authors.forename: Chris
authors.initials: C
authors.lastname: Harrod
authors.affiliation: Kilpisjärvi Biological Station, University of Helsinki, Käsivarrentie 14622, FI-99490, Kilpisjärvi, Finland.|Department of Environmental Sciences, University of Helsinki, PO Box 65, FI-00014, Helsinki, Finland.
authors.forename: Kimmo K
authors.initials: KK
authors.lastname: Kahilainen
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis; D004032:Diet; D005247:Feeding Behavior; D005260:Female; D005387:Finland; D005766:Gastrointestinal Contents / Q000737:chemistry; D060106:Lakes; D008099:Liver / Q000737:chemistry; D008297:Male; D009132:Muscles / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000032:analysis; D012098:Reproduction; D012487:Salmonidae / Q000254:growth & development / Q000502:physiology*; D012621:Seasons
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes
keywords: C:N ratio; Coregonus lavaretus; benthic macroinvertebrates; diet; multiple tissues; subarctic; trophic subsidies; zooplankton; δ13C; δ15N