| Food webs of benthic boundary layer zooplankton and the biogeochemistry of near-bottom water on the Beaufort Sea shelf were studied during fall 2003 and summer 2004. The influence of the Mackenzie River on the source, quantity, and quality of organic matter in near-bottom waters across the Beaufort Sea shelf was investigated by integrating chlorophyll, fatty acid, C, N, and P concentration and ratio, and delta13C data of particulate organic matter (POM). The Mackenzie River had a strong influence on the composition of POM in near-bottom waters across the entire Beaufort Sea shelf, including the Amundsen Gulf, with terrestrial markers, such as POM concentrations, fatty acid signatures and delta13C values, strongest near the river. An enhanced microbial fingerprint on near-bottom waters near the river was also observed based on C:N ratios and bacterial fatty acid signatures. Fatty acids allowed detection of a phytoplankton sinking event during summer that would not have been apparent using only C:N ratios and chlorophyll a. In addition, elemental composition (C, N, and P content and stoichiometry), lipid classes, fatty acids, and stable isotope ratios (delta13C and delta15N) were used to study the diets and energy storage of 26 taxa of benthic boundary layer zooplankton. This is the first report of the biochemical composition and trophic ecology of many of the amphipods and mysids presented here. Almost all taxa had high levels of wax esters or triacylglycerol, suggesting that benthic boundary layer zooplankton on the Beaufort Sea shelf are directly linked to intense seasonal pulses of primary production characteristic of high latitude seas. delta15N and fatty acid signatures indicate that there were diverse feeding modes among the taxa with trophic levels ranging from 2--4. Fatty acid profiles not only reflected diet but also phylogeny, with taxa of malacostracan crustaceans having similar fatty acid profiles. Phytoplankton fatty acid markers in copepods and chaetognaths indicate that the conventional, phytoplankton-copepod-chaetognath food web was also present in the benthic boundary layer. Using multiple biomarkers and tracers allowed for increased understanding of zooplankton feeding ecology and the sources of organic matter in near-bottom waters. |
