This content will become publicly available on July 1, 2024
- Award ID(s):
- 2115154
- NSF-PAR ID:
- 10479860
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Geochimica et Cosmochimica Acta
- Volume:
- 352
- Issue:
- C
- ISSN:
- 0016-7037
- Page Range / eLocation ID:
- 36 to 50
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Winemiller, KO. (Ed.)The widespread importance of variable types of primary production, or energy channels, to consumer communities has become increasingly apparent. However, the mechanisms underlying this “multichannel” feeding remain poorly understood, especially for aquatic ecosystems that pose unique logistical constraints given the diversity of potential energy channels. Here, we use bulk tissue isotopic analysis along with carbon isotope (δ13C) analysis of individual amino acids to characterize the relative contribution of pelagic and benthic energy sources to a kelp forest consumer community in northern Chile. We measured bulk tissue δ13C and δ15N for >120 samples; of these we analyzed δ13C values of six essential amino acids (EAA) from nine primary producer groups (n = 41) and 11 representative nearshore consumer taxa (n = 56). Using EAA δ13C data, we employed linear discriminant analysis (LDA) to assess how distinct EAA δ13C values were between local pelagic (phytoplankton/particulate organic matter), and benthic (kelps, red algae, and green algae) endmembers. With this model, we were able to correctly classify nearly 90% of producer samples to their original groupings, a significant improvement on traditional bulk isotopic analysis. With this EAA isotopic library, we then generated probability distributions for the most important sources of production for each individual consumer and species using a bootstrap‐resampling LDA approach. We found evidence for multichannel feeding within the community at the species level. Invertebrates tended to focus on either pelagic or benthic energy, deriving 13–67% of their EAA from pelagic sources. In contrast, mobile (fish) taxa at higher trophic levels used more equal proportions of each channel, ranging from 19% to 47% pelagically derived energy. Within a taxon, multichannel feeding was a result of specialization among individuals in energy channel usage, with 37 of 56 individual consumers estimated to derive >80% of their EAA from a single channel. Our study reveals how a cutting‐edge isotopic technique can characterize the dynamics of energy flow in coastal food webs, a topic that has historically been difficult to address. More broadly, our work provides a mechanism as to how multichannel feeding may occur in nearshore communities, and we suggest this pattern be investigated in additional ecosystems.more » « less
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Rationale Nitrogen isotopic compositions (δ15N) of source and trophic amino acids (AAs) are crucial tracers of N sources and trophic enrichments in diverse fields, including archeology, astrobiochemistry, ecology, oceanography, and paleo‐sciences. The current analytical technique using gas chromatography‐combustion‐isotope ratio mass spectrometry (GC/C/IRMS) requires derivatization, which is not compatible with some key AAs. Another approach using high‐performance liquid chromatography‐elemental analyzer‐IRMS (HPLC/EA/IRMS) may experience coelution issues with other compounds in certain types of samples, and the highly sensitive nano‐EA/IRMS instrumentations are not widely available.
Methods We present a method for high‐precision δ15N measurements of AAs (δ15N‐AA) optimized for canonical source AA‐phenylalanine (Phe) and trophic AA‐glutamic acid (Glu). This offline approach entails purification and separation via high‐pressure ion‐exchange chromatography (IC) with automated fraction collection, the sequential chemical conversion of AA to nitrite and then to nitrous oxide (N2O), and the final determination of δ15N of the produced N2O via purge‐and‐trap continuous‐flow isotope ratio mass spectrometry (PT/CF/IRMS).
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