Nitrogen sources and net growth efficiency of zooplankton in three Amazon River plume food webs

Authors

Natalie Loick-Wilde
Sarah C. Weber
Brandon J. Condon, Virginia Institute of Marine Science
Douglas G. CaponeFollow
Victoria J. Coles
Patricia M. Medeiros
Deborah K. Steinberg, Virginia Institute of Marine ScienceFollow
Joseph P. Montoya

Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

3-2016

Journal

Limnology and Oceanography

Volume

61

Issue

2

First Page

460

Last Page

481

Abstract

The plasticity of nitrogen specific net growth efficiency (NGE) in marine mesozooplankton is currently unresolved, with discordant lines of evidence suggesting that NGE is constant, or that it varies with nitrogen source, food availability, and food quality in marine ecosystems. Specifically, the fate of nitrogen from nitrogen fixation is poorly known. We use ¹⁵N : ¹⁴N ratios in plankton in combination with hydrological data, nutrient profiles, and nitrogen fixation rate measurements to investigate the relationship between new nitrogen sources and the nitrogen specific NGE in three plankton communities along the outer Amazon River plume. The NGE of small (200–500 μm) mesozooplankton was estimated from the δ ¹⁵N differences between particulate nitrogen and zooplankton using an open system Rayleigh fractionation model. The transfer efficiency of nitrogen among larger (> 500 μm) mesozooplankton was estimated from the change in δ ¹⁵N as a function of zooplankton size. The Amazon River was not a significant source of bioavailable nitrogen anywhere in our study region, and subsurface nitrate was the primary new nitrogen source for the outer shelf community, which was dominated by diatoms. N₂ fixation was the principal new nitrogen source at sites of high diatom diazotroph association abundance and at oceanic sites dominated by Trichodesmium spp. and Synechococcus spp. Although we found clear spatial differences in food quantity, food quality, and diazotroph inputs into mesozooplankton, our data show no significant differences in mesozooplankton nitrogen transfer efficiency and NGE (for latter, mean ± SD: 59 ± 10%) among sites.

DOI

doi: 10.1002/lno.10227

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.

Recommended Citation

Loick-Wilde, Natalie; Weber, Sarah C.; Condon, Brandon J.; Capone, Douglas G.; Coles, Victoria J.; Medeiros, Patricia M.; Steinberg, Deborah K.; and Montoya, Joseph P., Nitrogen sources and net growth efficiency of zooplankton in three Amazon River plume food webs (2016). Limnology and Oceanography, 61(2), 460-481.

doi: 10.1002/lno.10227