Bryozoan stable carbon and hydrogen isotopes: relationships between the isotopic composition of zooids, statoblasts and lake water
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We explored the extent to which δ13C and δD values of freshwater bryozoan statoblasts can provide information about the isotopic composition of zooids, bryozoan food and surrounding water. Bryozoan samples were collected from 23 sites and encompassed ranges of nearly 30‰ for δ13C and 100‰ for δD values. δ13C offsets between zooids and statoblasts generally ranged from −3 to +4.5‰, with larger offsets observed in four samples. However, a laboratory study with Plumatella emarginata and Lophopus crystallinus demonstrated that, in controlled settings, zooids had only 0–1.2‰ higher δ13C values than statoblasts, and 1.7‰ higher values than their food. At our field sites, we observed a strong positive correlation between median δ13C values of zooids and median δ13C values of corresponding statoblasts. We also observed a positive correlation between median δD values of zooids and statoblasts for Plumatella, and a positive correlation between median δD values of statoblasts and δD values of lake water for Plumatella and when all bryozoan taxa were examined together. Our results suggest that isotope measurements on statoblasts collected from flotsam or sediment samples can provide information on the feeding ecology of bryozoans and the H isotopic composition of lake water.
KeywordsFreshwater Bryozoa Stable isotopes Statoblasts Lakes Feeding ecology Palaeoecology
We thank Michiel van der Waaij for collecting samples in Dutch lakes and for useful information on the habitat and ecology of several freshwater bryozoan species (www.bryozoans.nl). Winfried Lampert, Peter Hammond, Alex Gruhl, and Elena Brand greatly helped during an exploratory field trip. Robert Dünner is kindly acknowledged for suggesting locations in a number of Swiss lakes. Peter Nyfeler’s work analysing the stable isotope data has been invaluable. We thank four anonymous reviewers for their comments on earlier versions of this manuscript. This study was funded by the European Research Council under the European Union’s Seventh Framework Programme (FP/2007–2013)/ERC Grant Agreement no. 239858 (RECONMET).
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