Carbon and nitrogen stable isotopes analysis of the common cephalopods beaks in the offshore of China

Abstract:

The beaks of cephalopods have stable chemical compositions and firm physical structures. Recently, with the increasing use of stable isotope analysis in ecology, it becomes a powerful tool and complement of traditional methods for investigating the trophic ecology and migration patterns of invertebrates. This research was based on 18 Uroteuthis duvauceli specimens, 18 Sepiella maindronis specimens, 20 Octopus ocellatus specimens and 15 Uroteuthis edulis specimens, which were collected in August 2013 from the East China Sea. The beaks of these four kinds of offshore species were studied by determining their carbon stable isotope(¹³C/¹²C,δ¹³C)and nitrogen stable isotope(¹⁵N/¹⁴N,δ¹⁵N).In order to find the differences of these species' habitats and the foraging behaviors, the δ¹³C and δ¹⁵N values were analyzed to see whether there was a correlation with their mantle lengths. The study aimed to explain the habitats of different cephalopods and find their position in the ecological system, not only providing materials for further development and management, but also giving a basis for the better use of these species. The results showed that the average values of mantle length for four species:U.duvauceli > U.edulis > S.maindroni > O.ocellatus(122.72mm > 67.93 mm > 67.93 mm > 35.3 mm). The average values of body weight for four species:U.duvauceli > S.maindroni > O.ocellatus > U.edulis > (70.39 g > 50.67 g > 47.35 g > 19.93 g). S.maindroni have the maximum δ¹⁵N value (10.81‰±0.38‰),the minimum δ¹³C value (-14.98‰±0.55‰),the minimum C/N(3.08±0.03)and U.edulishave the minimum δ¹⁵N value (8.21‰±0.30‰), the maximum δ¹³C value(-13.00‰±0.54‰), the maximum C/N(3.57±0.06), U.duvauceli and U.edulislive in the shallower water area than the S.maindroni and O.ocellatus. And the δ¹³C and δ¹⁵N values between U.duvauceli and O.ocellatus were very similar (ANOVA, P>0.05), their ecological niches were much overlapped, they may have the similar trophic level. The δ¹³C and δ¹⁵N values of other kinds of species had significant differences (ANOVA, P<0.05). In addition, the δ¹³C values of U.duvauceli and the mantle length (ML) showed a significant liner relationship (δ¹³C=0.023 6×L_ML- 17.429,P<0.05), δ¹⁵N values also showed a significant liner relationship with the mantle length (ML) (δ¹⁵N=0.017 6×L_ML+ 6.873,P<0.05), but there was no significant correlation between carbon and nitrogen stable isotopes with the mantle length in S.maindroni, O.ocellatus and U.edulis (P>0.05).It showed that there was no significant connection between feeding habit and mantle length.