ABSTRACT
We measured δ15N, δ13C, and percent carbon (C) and nitrogen (N) on foot and remaining soft tissue of the two native freshwater mussel species Echyridella aucklandica and E. menziesii (Hyriidae: Unionida) from three Waikato, northern New Zealand, streams to investigate differences among sites, sexes and species. Mean differences in δ15N and δ13C between foot and remaining soft tissue (mainly guts, gills and gonads) were <0.5‰, whereas %C and %N were higher in foot tissue and C:N values were lower. No differences were detected between mussel species, but δ15N and δ13C displayed marked differences among sites for both species, with δ15N variations consistent with the level of catchment land-use intensification. Variation in δ13C and δ15N among replicate mussels was low indicating few individuals are required to precisely characterise isotope signatures of local populations. The lack of evidence of trophic resource partitioning among species, and consistent differences in isotope ratios between sites, suggests that the more widespread and abundant E. menziesii may provide an effective baseline integrator of catchment activities that alter carbon supplies and nitrogen sources.
Acknowledgements
We thank landowners Brent Pini and Nora Palmer (Paepaeruru Trust) for access to the Ohautira site, Anjana Rajendram and Judy Hoult for performing the stable isotope analyses, and two anonymous referees for helpful reviews.
Disclosure statement
No potential conflict of interest was reported by the author(s).