Bryozoan stable carbon and hydrogen isotopes: relationships between the isotopic composition of zooids, statoblasts and lake water

We explored the extent to which delta C-13 and delta D 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 30aEuro degrees for delta C-13 and 100aEuro degrees for delta D values. delta C-13 offsets between zooids and statoblasts generally ranged from -3 to +4.5aEuro degrees, 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 0-1.2aEuro degrees higher delta C-13 values than statoblasts, and 1.7aEuro degrees higher values than their food. At our field sites, we observed a strong positive correlation between median delta C-13 values of zooids and median delta C-13 values of corresponding statoblasts. We also observed a positive correlation between median delta D values of zooids and statoblasts for Plumatella, and a positive correlation between median delta D values of statoblasts and delta D 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.