Temperature-dependent fractionation of stable oxygen isotopes differs between cuttlefish statoliths and cuttlebones

Abstract

• The first equation between temperature and δ 18 O values for cephalopod is established. • Carbonate δ 18 O values as a temperature proxy are structure specific. • The variation of δ 18 O values in biogenic carbonates is shown among marine organisms. The recording of oxygen isotope composition (δ 18 O) in biogenic carbonates is a powerful tool for investigating temperature changes in organisms’ habitats, especially in relation to their growth, migration, movement, adaptation, and acclimation. Temperature-dependent equations of δ 18 O values have been established from biogenic carbonates in various organisms, but no equation has yet been validated for cephalopods, thus limiting the application of this approach to the field of cephalopod ecology. In this study, we established a temperature-dependent equation of δ 18 O values in statoliths and cuttlebones of the pharaoh cuttlefish, Sepia pharaonis , through a controlled experiment involving three temperatures (20 °C, 25 °C, and 30 °C). The established equations for statoliths and cuttlebones follow the general trend in inorganic carbonates, fish otoliths, and mollusc shells, revealing that δ 18 O values are lower when the temperature is higher. Noticeably, the intercept and slope of the equations obtained from cuttlebones and statoliths differed even when these two carbonate structures formed within the same individual cuttlefish. The isotopic difference between statoliths and cuttlebones suggests that temperature-dependent fractionation is structure specific and may result from the functional demands and chemistry of the internal fluids surrounding these two biogenic carbonates. The use of δ 18 O values recorded in statoliths and cuttlebones as a temperature proxy can benefit studies of cephalopod ecology and thermal history.