| dc.description.abstract | Emergent aquatic insects subsidize the diets of terrestrial consumers and may transport toxic methyl mercury (MeHg) to terrestrial organisms (the "dark side" of subsidies). Terrestrial tetragnathid spiders are thought to consume emergent aquatic insects, and, in a previous study, we found a correlation between emergent insect-mediated MeHg flux and MeHg concentrations in spiders. In the present study, we used stable isotopes of nitrogen to determine the source of MeHg to tetragnathid spiders. We collected spiders and a variety of other aquatic and terrestrial taxa hypothesized to represent a range of trophic levels from 10 shallow ponds in north Texas, USA. Based on MeHg concentrations and stable nitrogen isotope ratios, we identified distinct aquatic- and terrestrial-based food chains. Terrestrial tetragnathid spiders belonged to the aquatic-based food chain, supporting the hypothesis that they are exposed to MeHg through their consumption of emergent aquatic insects. Additionally, our study suggests measurements of MeHg concentration coupled with stable nitrogen isotope ratios can help distinguish between aquatic and terrestrial food chains and may be effective tracers of aquatic subsidies to terrestrial ecosystems. | |
