Abstract
AbstractLittoral benthic primary production is considered the most important energy source of consumers in subarctic lakes. We analyzed essential fatty acid (EFA) and amino acid (EAA) content of 23 littoral benthic macroinvertebrate taxa as well as cladocerans and copepods from pelagic and littoral habitats of 8–9 subarctic lakes to compare their nutritional quality. Pelagic crustacean zooplankton had significantly higher EFA and total FA content (on average 2.6‐fold and 1.6‐fold, respectively) than littoral macroinvertebrates in all our study lakes. Specifically, docosahexaenoic acid (DHA), one of the most important EFA for juvenile fish, was almost exclusively found in pelagic copepods. In littoral macroinvertebrates, only Lymnaea (Gastropoda), Eurycercus (Cladocera), and Gammarus (Amphipoda) contained a low amount of DHA, whereas most littoral invertebrate taxa contained moderate amounts of eicosapentaenoic acid (EPA). The difference in DHA content may explain why so many generalist fish shift their diet to pelagic zooplankton at their peak abundance in mid/late‐summer. Meanwhile, the differences in EAA content between pelagic zooplankton and littoral invertebrates were much lower than for EFA suggesting a wider availability of EAA in subarctic lakes, except for methionine. In the studied subarctic lakes, EFA and EAA variation in consumers was more related to taxon‐specific than lake‐specific characteristics. This indicates that climate‐induced changes in the abundance and community structure of zooplankton vs. littoral macroinvertebrates will be important parameters in determining the availability of EFA and EAA to juvenile fish, and potentially fish production.
Highlights
IntroductionThe relative importance of the two habitats (pelagic and littoral) for consumers is interesting in northern ecosystems, which are experiencing rapid environmental changes, i.e., rising temperatures and precipitation, increasing terrestrial runoff and potential shifts in primary production toward pelagic dominance (Creed et al 2018; Hayden et al 2019)
Principal findings of the study Our study demonstrates that zooplankton and benthic macroinvertebrates, two major food resources for most fish in the subarctic region, differ more in their essential fatty acid (EFA) than essential amino acids (EAAs) content
Low average content of docosahexaenoic acid (DHA) in littoral macroinvertebrates and low methionine content in both pelagic zooplankton and littoral macroinvertebrates in all lakes was prominent in our data
Summary
The relative importance of the two habitats (pelagic and littoral) for consumers is interesting in northern ecosystems, which are experiencing rapid environmental changes, i.e., rising temperatures and precipitation, increasing terrestrial runoff and potential shifts in primary production toward pelagic dominance (Creed et al 2018; Hayden et al 2019) These may have profound effects on lake food webs, especially on the importance and quality of both pelagic and littoral primary producers as well as bacterial contribution to basal resources, available for invertebrate consumers and fish in the higher trophic levels (Ask et al 2009; Creed et al 2018; Hayden et al 2019; Bergström et al 2020). The current knowledge on FAs in dorsal muscle of whitefish suggest relatively stable annual composition, except lowered concentrations of EFA during physiologically demanding spawning period in winter (Sushchik et al 2007; Keva et al 2019)
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