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Free keywords:
benthic macroinvertebrates; C:N ratio; Coregonus lavaretus; d13C; d15N, diet; multiple tissues; subarctic; trophic subsidies; zooplankton
Abstract:
1. 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.
2. We undertook a year-long study of benthic (macroinvertebrate) and pelagic (zooplankton)
resource availability, along with short (day/days: stomach content)-, medium (month: liver
d13C and d15N isotopes)- and long-term (season: muscle d13C and d15N 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.
3. 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.
4. 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.
