Controls on the nitrogen isotopic composition of fish otolith organic matter: Lessons from a controlled diet switch experiment

The nitrogen isotopes (δ15N) in the organic fraction of accretionary hard part structures, such as fish otoliths, may provide life histories dietary change. We performed controlled experiments to validate dynamics isotopic signal incorporation into biominerals following shifts and also compared whole-otolith serial sampling approaches for diet reconstruction. Laboratory-reared Atlantic croaker (Micropogonias undulatus) were switched from a high quality, δ15N (δ15N = 10.7‰) one two lower diets 5.9 or 3.7‰). Using oxidation-denitrifier method, including cleaning protocols required fossil we measured both otolith-bound (δ15Noto) subsamples (δ15Nwhole) sequentially micromilled otolith powders (δ15Nmicro) these results white muscle tissue liver obtained through traditional techniques. Both δ15Nwhole δ15Nmicro recorded switch, although limitations muted δ15Nmicro, especially slowly growing otoliths on lowest quality diet, which accretion was particularly slow. timescales at tissues approached new after switch varied, but slowest fastest liver. For δ15Nwhole, there factors: (1) turnover time N provided (2) that is accreting thus integrating over entire history fish. model account growth, supplying growth ranged 12 16 days. In soft trophic discrimination factor (the elevation relative diet) appears have been larval fish, prior onset switches. This raises questions about interpretation δ15Noto cores; however, core typically minute portion total otolith. conclude useful tracking despite whole-life integration records higher resolution will require further optimization sampling.