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|Fish eye lens isotope profiles show lifetime movement and diet
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|University of South Florida College of marine Science
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Trophic relationships and to movement may be inferred using stable isotopes in a wide variety of organisms, but time frames are usually limited by tissue turn-over. The laminar structure of vertebrate eye lenses provides isotope records for the lifetime of the individual. We analyzed the δ13C and δ15N in sequential eye-lens laminae of two demersal, mesopredator fishes in the eastern Gulf of Mexico, Tilefish (Lopholatilus chamaeleonticeps) and Red Grouper (Epinephelus morio). In Tilefish, both δ13C and δ15N increased consistently throughout life. Progressions of δ13C and δ15N in eye-lens laminae had a strong correlation with eye-lens diameter, and strong correlations between the two isotopes were present in all specimens, reflecting trophic growth and little lifetime movement. In Red Grouper, δ15N increased consistently, but δ13C did not. Eye-lens diameter correlated strongly with δ15N, but trends in δ13C were irregular, often consistent with movement across the regional δ13C gradient. Correlations between δ15N and δ13C were also weak in Red Grouper, suggesting cross-shelf ontogenetic movements. These results can be used to assess lifetime movement in other fish species inhabiting decoupled isoscapes. A strong correlation between δ13C and δ15N in the eye-lens indicates trophic growth and high lifetime site fidelity while a weak correlation between isotope profiles indicates trophic growth coupled with ontogenetic movement.