Estuaries and Coasts

, Volume 32, Issue 6, pp 1152–1164 | Cite as

Stable Isotopes Reveal Complex Changes in Trophic Relationships Following Nutrient Addition in a Coastal Marine Ecosystem

Article

Abstract

Complex links between the top-down and bottom-up 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.

Keywords

Caridean Gastropod Palatability Shoalgrass Turtle grass Epiphytes Nutrients 

Supplementary material

12237_2009_9219_MOESM1_ESM.docx (17 kb)
Supplementary data(DOC 17 kb)

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Copyright information

© Coastal and Estuarine Research Federation 2009

Authors and Affiliations

  1. 1.Department of Marine BiologyTexas A&M University at GalvestonGalvestonUSA
  2. 2.Department of Biological Sciences and Southeast Environmental Research Center, Marine Science ProgramFlorida International UniversityNorth MiamiUSA

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