13C and 18O isotopic disequilibria in fish otoliths: metabolic and kinetic effects

Abstract

Distnbution of oxygen and carbon stable isotopes in fish otoliths from a wide range of species was invesugated to determine if the isotopes were deposited in equilibnum with ambient seawater and the potential utihty of isotope data to studies of fish biology Companson of 6180 and 6 I 3 c data from otoliths w t h estimates of equilibnurn aragonite indicate that ''0, but not I3C was deposited near equdibnum and this confirms the utllity of otolith oxygen isotopes as an indicator of ambient temperature The departure of 613C from equilibrium was considered In light of several current theones on 13c isotope disequilibrium There was a strong correlalon between bI3C and temperature and, concomitantly a strong relationship between 6180 and 6I3C Evldence is presented to support the Importance of metabolic effects in medialng I3C disequdibna and a strong relationship between metabohc rate (VO?) and 6I3c is hypothesized F ~s h e s with low metabolic rates or those living at low temperatures had 13C deposited near to equilibnum whereas fishes living at higher temperatures showed extreme depletion in otolith I3C Trends were also evident in 613C values in luveniles and adults of a species with the juveniles presumably with a higher metabolic rate being more depleted in I3C than the adults The study shows that both oxygen and carbon stable isotopes have great potential in studies of fish biology and are worthy of further investigation