Alanine δ15N trophic fractionation in heterotrophic protists
Abstract
We evaluated differences in the15N isotopic enrichment factors of trophic amino acids (AA) for protistan (microzooplankton) and metazoan (mesozooplankton) consumers, testing the hypothesis that δ15N of alanine (ala) increases in both consumer types, while glutamic acid (glu) enriches mainly in mesozooplankton. AA δ15N values were measured for dinoflagellate and ciliate grazers and their respective algal prey (Oxyrrhis marina/Dunaliella tertiolectaandFavellasp./Heterocapsa triquetra) in four two‐stage chemostat experiments, including treatments with different nitrogen : phosphorous nutrient ratios and light/dark recycling conditions. Propagation of AA15N enrichment to a metazoan consumer was also assessed in two‐ and three‐stage chemostat experiments simulating simple “classical” (Calanus pacificusand the diatomThalassiosira weissflogii) and “multivorous” (C. pacificus,O. marina, andD. tertiolecta) food chains. We found small or negligible15N‐enrichment of glu for both protistan grazers, while ala enrichment was consistently greater and similar to that in metazoan consumers. Ala and glu δ15N values were both highly elevated inC. pacificusrelative to prey, and enrichment was higher with autotrophic diets. These laboratory results suggest that ala may be used as an alternate, accurate isotopic proxy for quantifying protistan contributions to trophic structure in aquatic systems.
Faculty Members
- Moira Décima - National Institute of Water and Atmosphere Research (NIWA) Wellington New Zealand
- Michael R. Landry - Scripps Institution of Oceanography, University of California at San Diego La Jolla California
- Marilyn L. Fogel - Department of Earth Science/Environmental Science University of California Riverside Riverside California
- Christina J. Bradley - Department of Biological Sciences Salisbury University Salisbury Maryland
Themes
- Isotopic enrichment of amino acids
- Differences in nutrient assimilation between consumer groups
- Use of isotopic proxies in ecological research
- Role of protists in food webs
- Trophic dynamics in aquatic ecosystems
Categories
- Ecology
- Ecology and evolutionary biology
- Marine sciences
- Geosciences, atmospheric, and ocean sciences
- Biological and biomedical sciences
- Biochemistry and molecular biology
- Biochemistry, biophysics, and molecular biology
- Ocean marine sciences and atmospheric science
- Biochemistry
- Oceanography, chemical and physical
- Marine biology and biological oceanography
- Epidemiology and biostatistics
- Ecology, evolutionary biology, and epidemiology
- Molecular biology