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Methyl mercury and stable isotopes of nitrogen reveal that a terrestrial spider has a diet of emergent aquatic insects

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Terrestrial spiders transfer methyl mercury (MeHg) to terrestrial consumers like birds but how spiders become contaminated with MeHg is not well understood. In the present study, we used stable isotopes of nitrogen in combination with MeHg to determine the source of MeHg to terrestrial long‐jawed orb weaver spiders (Tetragnatha sp). We collected spiders and a variety of other aquatic and terrestrial taxa 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. Long‐jawed orb weaver spiders belonged to the aquatic‐based food chain, indicating that they are exposed to MeHg through their consumption of emergent aquatic insects. Additionally, our study suggests that ecologists can use stable isotopes of nitrogen (δ15N) in conjunction with MeHg speciation analysis to distinguish between aquatic and terrestrial food chains. Environ Toxicol Chem © 2014 SETAC

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