Fig. 5
Stable isotopic content of food sources and consumers. a Carbon and deuterium stable isotope ratios (13C/12C, 2H/1H) from stygobitic shrimp (diamonds) and surface insects (triangles) plotted relative to CH4 and soil-derived organic matter (OM) end members. Proximity to source indicates relative trophic dependency. The δ13C value of methane from the MFW (−66.3 ± 0.7‰, red shaded area) is consistent with a microbial source29 (gray shaded area). The δ13C of the soil-derived OM (−28.0 ± 0.2‰, green shaded area) includes values for forest soil, cave POC, and cave DOC. b Fatty acids from stygobitic shrimp specimens. Methane-derived carbon contribution is higher (55%) for shrimp 1 (orange) and lower (3%) for shrimp 2 (blue) based on bulk δ13C values (−49.1‰ and −29.3‰, respectively). The combination of extremely negative δ13C values and bacterial origins for odd-numbered monounsaturated and methylated FAs indicates a bacterial food source that is likely to include aerobic methanotrophs. Symbols of individual data points contain the uncertainty (std. dev.) of the measured isotopic values
