Nutritional quality of littoral macroinvertebrates and pelagic zooplankton in subarctic lakes

Abstract

Littoral 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.

Increasing temperature and productivity change biomass, trophic pyramids and community‐level omega‐3 fatty acid content in subarctic lake food webs

“…Since, benthic macroinvertebrates included only a minor amount of DHA as reported also previously, zooplankton is clearly the most likely dietary source of DHA for fish (e.g. Makhutova et al, 2016;Vesterinen et al, 2020). The EPA + DHA content of fish muscle did not differ among feeding habitats (zooplanktivore, benthivore, piscivore), possibly providing evidence for selective transfer or utilization of FAs in fish (Strandberg et al, 2015).…”

“…We combined a small subset of fatty acid data from previous studies having a different focus (Taipale et al., 2016; Vesterinen et al., 2020). Total dataset consisted of 868 samples (Table S2: phytoplankton = 32, zooplankton = 26, littoral benthos = 209, profundal benthos = 34, invertivorous fish = 377, piscivorous fish = 190).…”

“…We combined a small subset of fatty acid data from previous studies having a different focus (Taipale et al, 2016;Vesterinen et al, 2020).…”

Depth-specific benthic specialization of Arctic char in an oligotrophic subarctic lake

“…Due to the limited competition for prey from other species in Lake Nerka, it is likely that such resource polymorphism would result from intra-specific competition for limited prey. It is still surprising, however, that a subset of Arctic char specializes on snails considering the greater nutritional value of pelagic-derived prey (i.e., sockeye salmon smolts or threespine sticklebacks) in comparison to benthic macroinvertebrates (Vesterinen et al 2020). Future work analyzing the resource polymorphism of Arctic char in Lake Nerka could help explain our observed feeding specialization and add to the body of literature documenting phenotypic plasticity in Arctic char worldwide.…”

Selective Fatty Acid Retention and Turnover in the Freshwater Amphipod Pallaseopsis quadrispinosa

“…The EPA in juvenile P. quadrispinosa was also higher than previously observed in zooplankton (8–18% of all FA) in a large boreal lake [ 22 ], and the cumulative contribution of EPA and DHA is equivalent to previous findings reported for calanoid zooplankton (26–45% of all FA). However, even though the total FA content of P. quadrispinosa and other gammarid amphipods [ 57 ] is much higher than in benthic invertebrates [ 61 ], the total FA content as well as EPA and DHA is usually highest in freshwater calanoids [ 62 ]. The observation that P. quadrispinosa has similar EPA and DHA levels to calanoids highlights that P. quadrispinosa may have relatively high nutritional value for fish.…”