THE TROPHIC STATUS OF MARINE TURTLES AS DETERMINED BY STABLE-ISOTOPE ANALYSIS

Stable isotope ratios of nitrogen and carbon were determined in bone c ollagen, egg proteins and keratin from epidermal carapace scutes of lo ggerhead Caretta caretta, green Chelonia mydas, and leatherback Dermoc helys coriacea turtles from the Mediterranean Sea and the European Atl antic Ocean; Isotope ratios in proteins from loggerhead turtles indica te that this species occupies a higher trophic position than green tur tles. Leatherback turtles are apparently intermediate in trophic statu s. Within loggerhead turtles, both isotope ratios correlated positivel y with body size, indicating a trend of increasing trophic level with age. Within the size range of green turtles sampled, there was apparen tly no change in trophic level in relation to body size. In absolute t erms, isotope signatures of egg proteins were markedly different from those of bone collagen. However, inter-specific differences in isotope values were consistent with those in bone protein. The novel applicat ion of this technique to marine turtles generally confirmed dietary in formation collected conventionally in these species and has also affor ded additional insights into shifts in diet and trophic status as turt les mature.