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Abstract A quantitative understanding of the mesopelagic zooplankton food web is key to development of accurate carbon budgets and geochemical models in marine systems. Here we use compound specific nitrogen stable isotope analysis of amino acids to quantify the trophic structure of the microzooplankton and mesozooplankton community during summer in the subarctic northeast Pacific Ocean during the EXport Processes in the Ocean from Remote Sensing (EXPORTS) field campaign. Source amino acid values in particles and zooplankton provide strong evidence that basal resources for the mesopelagic zooplankton food web were primarily small (), suspended or slow‐sinking particles, but that surface organic matter delivered by vertically migrating zooplankton may have also been important. Comparisons of values of source and trophic amino acids provide estimates of food web length, which decrease significantly with depth and suggest that protistan microzooplankton are key components of the food web from the surface to at least 500. These results emphasize the importance of small particles as a source of carbon and nitrogen to mesopelagic communities in this region, support observations of an inverse relationship between zooplankton vertical migration and small particles as sources of carbon to deep‐sea food webs in low productivity environments, and document the role of heterotrophic protists as key trophic intermediaries in the mesopelagic zone at this location.
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Decadal-scale changes in the Georges Bank ecosystem: evidence from bulk and compound-specific stable isotope analyses of fish scales
The impacts of climate change are increasingly apparent in the physical oceanographic environment of the global ocean, with cascading effects through individual species to entire food webs. Despite their importance, these ecosystem effects can be challenging to quantify and track. One angle from which to analyse ecosystem linkages is via compound-specific stable isotope analysis of carbon and nitrogen focused on individual amino acids. These analyses can provide individual-level information (e.g., dietary sources, trophic position) as well as ecosystem-level information (e.g., variability in biogeochemical cycling at the base of the food web, nutrient regimes, food web structure). In this study, we analyzed C and N stable isotopes in archived scales of haddock (Melanogrammus aeglefinus) collected over almost a century from Georges Bank (northeast US) to investigate changes in the diet and trophic status of the haddock population driven by climate change. Specifically, we used nitrogen isotopes to identify secular changes in the input of warm slope waters to the Gulf of Maine over the time series. In contrast, carbon isotopes in essential amino acids suggest that there have been relatively small changes in the source of carbon fueling haddock biomass over the past 100 years and nitrogen isotopes indicate negligible changes in haddock trophic position despite major oceanographic and climatic changes over this time period. Overall, we demonstrate the application of cutting edge molecular isotope tools to a historical archive to examine food web architecture over time in a changing oceanographic environment.
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- Award ID(s):
- 2049307
- PAR ID:
- 10501398
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Ocean Sciences Meeting
- Format(s):
- Medium: X
- Location:
- New Orleans, LA
- Sponsoring Org:
- National Science Foundation
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