MEPS 240:85-92 (2002)  -  doi:10.3354/meps240085

ABSTRACT: Modifications to a conventional elemental analyzer-stable isotope ratio mass spectrometer system (EA-MS system) are described that allow the analysis of ¹³C and ¹⁵N in small samples (≥1 µgN and 2 µgC). This system was to analyze δ¹³C and δ¹⁵N of meiofaunal species from a coastal marsh using pooled samples of 5 to 60 individuals. In a conventional field survey, ¹³C and ¹⁵N isotope values indicated that (1) harpacticoid copepod species, nematode species, and ostracods differentially exploited phytoplankton detritus, Spartina alterniflora detritus, and benthic microalgae, and (2) all taxa showed a general shift toward S. alterniflora isotope values in winter relative to summer. In a field experiment, benthic microalgae were labeled in situ by addition of ¹³C and ¹⁵N to 1 m² sediment plots. Two nematode species with apparently similar primary food resources (S. alterniflora detritus) based on natural isotopic values differed dramatically in their uptake of ¹³C and ¹⁵N in labeled plots, indicating differences in feeding strategies that were not indicated by natural isotope values. A combination of natural-abundance isotope surveys and isotope-addition experiments appears to be a powerful approach for investigating both average patterns and interspecific variability in resource exploitation.

KEY WORDS: δ¹³C · δ¹⁵N · Meiofauna · Harpacticoids · Nematodes · Ostracods · Benthic microalgae · Spartina