Comparing Trophic Level Position of Invertebrates in Fish and Fishless Lakes in Arctic Alaska

Arctic lakes are likely very sensitive to the effects of climate change. Thus it is important to understand the current food web dynamics and energy flow within these lakes, to better understand how they will change in the future due to the effects of a rapidly changing climate. In order to contribute to this understanding, my project consists of an analysis of stable isotopes of carbon (delta 13 C) and nitrogen (delta 15 N) from invertebrates among fish and fishless lakes in arctic Alaska, to compare their trophic level positions and primary energetic sources. I collected pelagic invertebrates from 5 different lakes, 2 of which have resident fish populations and 3 of which are fishless. I analyzed and compared the stable isotope results with isotopic data collected from other related projects and one additional fish-inhabited lake. With this analysis, I created food webs to: 1) assign trophic positions to each species in each lake and compare those positions across lakes; and 2) assess the potential effect fish predation has on pelagic invertebrate community structure. I hypothesized that fish predation will determine zooplankton community structure and alter trophic linkages. This was proven to be true in the case of one fishless lake, whose predacious zooplankton\u27s trophic position was the same as the fish in the other lakes. However, for the two other fishless lakes, the trophic position of the predacious and herbivorous zooplankton decreased. The decrease was possibly due to much smaller sizes of the fishless lake, or the unexamined presence of another predatory invertebrate .