Analysis of the isotope composition of calcareous structures of marine organisms has proved useful in providing biological data. The present study constitutes the first detailed work undertaken on the isotope composition of coleoid cephalopods. We analysed the carbon- and oxygen-isotope composition [δ13C (CO2− 3) and δ18O (CO2− 3), respectively] of the cuttlebone aragonite of wild and cultivated specimens of Sepia officinalis Linnaeus, 1758. δ13C (CO2− 3) ranged from −2.94 to 1.00‰, δ18O (CO2− 3) from −0.18 to 2.08‰. The carbon-isotope composition is not in equilibrium with the carbon species of the ambient seawater, and does not reflect the deposition of CaCO3 in seawater. The potential influence of environmental factors and biological processes on the carbon-isotope composition of the cuttlebone is discussed. In contrast to δ13C, the oxygen-isotope composition of cuttlebone aragonite appears to be in isotopic equilibrium with the ambient seawater. Seasonal changes in isotopic temperature revealed by our analyses agreed with changes in the temperature of the ambient seawater. CaCO3 was deposited all year round. A maximum life span of 2 yr, a year-round spawning season, and variable growth rates among and within individuals have been inferred from the isotopic temperatures.

This work is a part of a PhD thesis by V. Bettencourt, funded by JNICT-Portugal (Praxis XXI/BD/4561/94) and supported by CICYT (MAR 95-1919-C05).

7 páginas, 4 figuras, 4 tablas

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