Stable C and N isotope concentration in several tissues of the loggerhead sea turtle <i>Caretta caretta</i> from the western Mediterranean and dietary implications

Abstract

SUMMARY:The isotopic concentrations of carapace scutes, skin, muscle and blood of loggerhead sea turtles (Caretta caretta) from the Balearic Archipelago were analysed to investigate the pattern of variation between tissues and to assess the position of this species in the trophic webs of the Algerian Basin. Skin showed higher δ 13 C values than muscle or carapace scutes and these showed higher values than blood. Conversely, muscle showed higher δ 15 N values than skin, skin showed higher values than blood and blood showed higher values than carapace scutes. Dead and live sea turtles from the same habitat did not differ in the concentration of stable isotopes. However, some of the tissues of the turtles caught in drifting longlines in the oceanic realm showed higher δ 13 C values than those from the turtles caught by hand or in trammel nets over the continental shelf, although they did not differ in the δ 15 N. Comparison of the concentration of stable isotopes in the turtles with that of other species from several areas of the Algerian Basin revealed that they consumed planktonic prey and that the trophic level of the sea turtles was higher than that of carnivorous cnidarians but lower than that of zooplanktophagous fish and crustaceans.Keywords: tissues, stable isotopes, sea turtle, trophic level, feeding ecology, carbon, nitrogen. RESUMEN: CONCENTRACIÓN DE ISÓTOPOS ESTABLES DE C Y N EN VARIOS TEJIDOS DELA TORTUGA BOBA CARETTA CARETTA DEL MEDITERRÁNEO OCCIDENTAL E IMPLICACIONES SOBRE LA DIETA. -La concentración isotópica de escudos del caparazón, piel, músculo y sangre de tortuga boba (Caretta caretta) fueron analizados para investigar el patrón de variación entre tejidos y para evaluar la posición de esta especie en las redes tróficas de la cuenca Argelina. La piel presentaba valores más altos de δ 13 C que el músculo o los escudos del caparazón y éstos presentaban valores más altos que la sangre. En cambio, el múscu-lo presentaba valores más altos de δ 15 N que la piel, ésta valores más altos que la sangre y ésta valores más altos que los escudos del caparazón. Las tortugas muertas y las vivas del mismo hábitat no diferían en la concentración de isótopos estables. Sin embargo, alguno de los tejidos de las tortugas capturadas mediante palangre de superficie en el medio oceánico presentaban valores más altos de δ 13 C que los de las tortugas capturadas a mano o mediante trasmallo en la plataforma continental, aunque no diferían en el δ 15 N. La comparación de la concentración de isótopos estables de tortuga con la de otras especies de varias áreas de la cuenca Argelina reveló que consumían presas planctónicas y que el nivel trófico de las tortugas era superior que el de los cnidarios carnívoros pero inferior que el de peces y crustáceos zooplanctófagos.

Bycatch of loggerhead sea turtles: insights from 14 years of stranding data

“…This suggests that large juvenile loggerheads in the western Mediterranean exploit pelagic habitats (Laurent et al 1998, Revelles et al 2007a) and may not adhere strictly to the typical ontogenic pattern of habitat use proposed for the species (Bolten 2003). This is supported by the importance of pelagic feeding in large juvenile loggerhead revealed in dietary studies in the western Mediterranean (Tomás et al 2001, Revelles et al 2007b). Moreover, satellite tracking studies of this species have now also highlighted pelagic habitat use by large juveniles (Revelles et al 2007a, McClellan & Read 2007 and adults (Hatase et al 2002, Hawkes et al 2006, indicating an ever-more complicated picture of multiple lifehistory strategies (Witzell 2002, Godley et al 2008.…”

Stable isotopic comparison between loggerhead sea turtle tissues

“…Because lipid extraction is unlikely to affect the δ 13 C or δ 15 N values of scute, we are confident that the samples in this study are comparable. [23,34,35] Juvenile [36] Epidermis Adult [11,28,[37][38][39][40] Juvenile [20,36,[41][42][43][44] Hatchling [20,38] Whole blood Juvenile [36] Red blood cells Adult [39,45] Juvenile [20,46] Hatchling [20] Plasma Adult [39] Juvenile [20,46,47] Hatchling [20] Muscle Juvenile [36,44] Hatchling [48] Bone Adult [49] Juvenile [50][51][52] Yolk Egg [9,35,[53][54][55] Whole egg Egg [50] Whole embryo Egg [50] Whole hatchling Hatchling [50] H. Scute biopsies were glued ventral side down with the dorsal surface (oldest tissue) exposed, and 50 μm layers were obtained using a carbide end mill (Sherline 5100 with digital readout; Vista, CA, USA). This interval was selected as the smallest interval that would provide sufficient sample mass for stable isotope analy...…”

Effect of tissue decomposition on stable isotope signatures of striped dolphins Stenella coeruleoalba and loggerhead sea turtles Caretta caretta

“…However, research on endangered species, such as marine mammals and sea turtles, often involves using the carcasses of animals involuntarily killed as a result of human interactions or stranded for other reasons (e.g. Godley et al 1998, Revelles et al 2007a,b, Arthur et al 2008, Cardona et al 2009, Pinela et al 2010, Fernández et al 2011, Gómez-Campos et al 2011. Carcasses may be found in various stages of decomposition (Kuiken & García Hartmann 1993), with tissue degradation potentially altering isotope signatures.…”