Stable isotopes reveal complex changes in trophic relationships following nutrient addition in a coastal marine ecosystem

Authors

Anna R. Armitage, Department of Biological Sciences and Southeast Environmental Research Center, Florida International UniversityFollow
James W. Fourqurean, Department of Biological Sciences and Southeast Environmental Research Center, Florida International UniversityFollow

Abstract

Complex links between the top-down and bottomup forces that structure communities can be disrupted by anthropogenic alterations of natural habitats.We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass (Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility. At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships, and, ultimately, the productivity values of the ecosystem.

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Post Print Version.

Copyright © 2009 Springer.

The definitive publisher-authenticated version is available online at http://dx.doi.org/10.1007/s12237-009-9219-z

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Armitage, A.R., J.W. Fourqurean. 2009. Stable isotopes reveal complex changes in trophic relationships following nutrient addition in a coastal marine ecosystem. Estuaries and Coasts 32: 1152-1164.