STABLE-ISOTOPE AND AMINO-ACID PROFILES OF THE NEW-ZEALAND GIANT PLIOCENE OYSTER CRASSOSTREA INGENS

Oxygen and carbon stable-isotope profiles and intracrystalline amino acid profiles (free and total) were determined for the New Zealand giant Pliocene oyster Crassostrea ingens by sampling annual growth increments along a sagittal section. These profiles reflect both ontogenetic and environmental change over the life-time of the oyster (approximately 20 years). There is a gradual increase in delta(18)O from the umbo towards the shell margin and a subsequent levelling-off about halfway along the shell. This pattern probably reflects a decrease in the growth rate of the oyster rather than a temperature effect. The delta(13)C profile initially increases sharply at the umbo and then gradually decreases towards the shell margin. This maybe due to kinetic or metabolic effects associated with the development of a fast-growing juvenile into a slower-growing, sexually mature adult, or it may be due to the influence of C-13-depleted carbon derived from the oxidation of organic matter in the surrounding sediment. The amino acid profile reveals a gradual decrease in abundance from the umbo to the shell margin, indicative of a progressive increase in the relative amounts of inorganic carbonate to protein over the life of the oyster, that may also be a consequence of decreasing growth rate. Glycine and alanine are the two most common amino acids in both the free and total amino acid profiles: free (i.e. naturally hydrolysed) amino acids account for about three quarters of the total amino acids present.