Diary of a bluegill (Lepomis macrochirus):: daily δ13C and δ18O records in otoliths by ion microprobe

Otoliths provide information about an individual fish's environment at ecologically relevant time scales. We used ion microprobe analysis to produce high-resolution delta C-13 and delta O-18 time series from two age-4 bluegill (Lepomis macrochirus) otoliths, which provided insight into fish behavior and otolith fractionation processes. Scanning electron microscope images revealed delta C-13 and delta O-18 pit diameters of 10 and 15 mu m, respectively, corresponding to 1-5 and 29 daily increments during rapid otolith growth and 6-9 and 12-25 increments near annual otolith growth checks. Spot-to-spot reproducibility (1 SD) of the calcite standards was <0.2 parts per thousand for delta O-18 and <0.4 parts per thousand for delta C-13 and was small enough to resolve a change in a fish's ambient temperature of approximately 1 degrees C. A whole-take C-13 addition experiment elevated the delta C-13 of the lake's dissolved inorganic carbon for 56 days during the summer of 2005. Mixing model results indicated that the proportion of dietary carbon in otoliths (M) was similar for both fish (BLG-3, M = 0.45; BLG-12, M = 0.35), but the relation between M and proxies of metabolic rate differed between fish. Otolith stable isotope analysis by ion microprobe can reveal the environmental history of an individual fish and contribute to our understanding of processes that influence isotope ratio fractionation in otoliths.