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Free keywords:
δ¹³C; δ¹⁵N; stable isotope analysis; food web; lake size; pelagic; benthic-littoral
Abstract:
Analysis of carbon and nitrogen stable isotopes has allowed freshwater ecologists to examine lake food webs in increasing detail. Many such studies have highlighted the existence of separate within-lake pelagic and benthic-littoral food webs but are typically conducted on large (> 10km²) lakes, whereas the majority of lakes are actually relatively small. We used stable isotope analysis (δ¹³C & δ¹⁵N) to examine trophic interactions between fish and their prey in Plußsee, as an example of a small, stratifying lake, and to determine whether separate pelagic/benthic-littoral food webs could be distinguished in such systems. Our results indicate that the Plußsee food web was complicated, and due to extensive intra-annual isotopic variation in zooplankton (e. g. cladoceran δ¹³C annual range = 25.6%), it may be impossible to definitively assign consumers from small, eutrophic stratified lakes to pelagic or benthic-littoral food webs. We present evidence that some components of the Plußsee food web (large bream) may be subsidised by carbon of methanogenic origin.
