Food Sources

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Cody Johnson and Chris Luecke weigh and measure recaptured arctic char for estimation of growth rates.

Arctic Alaska contains hundreds of thousands of lakes, almost all quite shallow. Research at the Arctic LTER on shallow lakes demonstrates that the food webs leading to fish are based mostly on primary production by bottom-dwelling algae rather than on plankton food webs. Yet, arctic fishery biologists continue to emphasize planktonic food webs and recent reviews of climate change in arctic freshwaters pay little attention to the benthic food web.

Comparisons of benthic and pelagic (i.e., excluding the lake bottom) primary production in lakes of various depths indicated that benthic production accounted for almost three quarters of total primary production in shallow lakes, and almost half of the primary production in deeper lakes (Whalen et al. 2008). Additions of 15N to the upper waters of lakes demonstrated that almost all of the production of fish was derived from the benthic food web (Hershey et al. 2006). Benthic invertebrates--mostly insects and snails living on the lake bottom--also impact nutrient cycling regimes in arctic lakes through grazing activities on benthic algae (Gettel et al. 2007). Snail enclosure experiments demonstrated that rates of nitrogen fixation increased with the density of snails. Results of these whole-lake and enclosure experiments represent some of the best examples of how animals influence nutrient cycling regimes in lake ecosystems.

Stomach contents of arctic grayling from 6 lakes showing the reliance of this fish on benthic prey
For further reading: 
Hershey, A.E., S. Beaty, K. Fortino, S. Kelly, M. Keyse, C. Luecke, W.J. O'Brien, and S.C. Whalen. 2006. Stable isotope signatures of benthic invertebrates in arctic lakes demostrate limited coupling to pelagic production. Limno. Ocenogr. 51:177-188.
Gettel, G.M., A.E. Giblin, and R.W. Howarth. 2007. The effects of grazing by the snail Lymnaea elodes on benthic N2 fixation and primary production oligotrophic, arctic lakes. Limnol. Oceanogr. 52:2398-2409.
Whalen, S.C., B. A. Chalfant, and E.N. Fischer. 2008. Epipelic and pelagic primary porduction in Alaskan Arctic lakes of varying depth. Hydrobiologia 614:243-257.
For further information: 
Chris Luecke
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