Stable isotope records from Sepia officinalis—a key to understanding the ecology of belemnites?

The stable isotope ratios (δ18O, δ13C) of the aragonite of cuttlebones of Sepia officinalis were measured on a high resolution scale where every septum was measured. Our studies aim at understanding whether variations of the isotope signature are controlled by ontogenetic and/or ecological factors. Five specimens were reared from eggs under known water temperatures, a sixth specimen was caught in the German part of the North Sea. The data suggest that the oxygen isotope composition is in isotopic equilibrium with the surrounding seawater and reflects ambient temperature. Migration and seasonal temperature changes are visible in the acquired data set. The carbon isotope signature shows signs of biofractionation and no direct correlation to the oxygen signature as far as ontogeny and ecology are concerned.