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

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