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Marine Ecology Progress Series

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MEPS 189:289-294 (1999)  -  doi:10.3354/meps189289

15N enrichment as a method of separating the isotopic signatures of seagrass and its epiphytes for food web analysis

M. A. Winning1,*, R. M. Connolly2, N. R. Loneragan3, S. E. Bunn1

1Centre for Catchment and In-Stream Research, Faculty of Environmental Sciences, Griffith University, Nathan, Queensland, 4111, Australia
2School of Environmental and Applied Science, Gold Coast campus, Griffith University, PMB 50, Gold Coast Mail Centre, Queensland 9726, Australia
3CSIRO Division of Marine Research, Cleveland Marine Laboratories, PO Box 120, Cleveland, Queensland 4163, Australia

ABSTRACT: Stable isotope analysis of food webs is of limited use where there is little or no difference in the natural abundance isotopic ratios of potential food sources. 15N-enriched potassium nitrate was used to differentially label 2 potential food sources for seagrass fauna: seagrass and its attached epiphytes. Different combinations of exposure time to the enriched substrate and different concentrations of enriched substrate were used to maximise the difference in δ15N signature between the 2 food sources. After adding the enriched substrate δ15N values of epiphytes ranged from 87 to 713o/oo, and were consistently higher than the δ15N values of seagrass, which ranged from 25 to 90o/oo. Enriched substrate additions every 3 d resulted in the greatest sustained separation between seagrass and epiphytes over 18 d. The results demonstrate that enriched 15N tracers are useful for separating the δ15N signatures of previously difficult to distinguish primary sources, and that this technique has the potential to resolve ambiguous natural abundance isotope results.

KEY WORDS: Algae · Stable isotopes · 15N-enriched isotope tracers · Trophic webs · Zostera capricorni

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