Stable isotope fractionation in the digestive gland, muscle and gills tissues of the marine mussel Mytilus galloprovincialis

Mytilus galloprovincialis is a common species in the Mediterranean. It is a sedentary filter-feeding organism that assimilates carbon and nitrogen isotopic ratios in tissues from its food sources. The δ13C and δ15N values have been used to demonstrate differences in isotopic composition between digestive gland, muscle and gills of this mussel. For δ13C, mean values were - 21.99 ± 0.50‰, - 19.70 ± 0.44‰, and - 19.96 ± 0.44‰, respectively; and for δ15N, they were 5.16 ± 0.90‰, 7.67 ± 0.79‰ and 7.77 ± 0.85‰, respectively. The fractionation or enrichment factor for 13C values between digestive gland and muscle, between digestive gland and gills, and between muscle and gills were - 2.29 ± 0.16‰, - 2.04 ± 0.14‰ and 0.27 ± 0.07‰, respectively, within the expected range of 13C fractionation at filter feeders reported elsewhere. In contrast, low fractionation values were found for 15N with - 2.45 ± 0.24‰, - 2.51 ± 0.16‰ and - 0.11 ± 0.16‰, between digestive gland and muscle, between digestive gland and gills, and between muscle and gills, respectively. Through isotopic fractionation of M. galloprovincialis, the depleted values were found in the digestive gland, followed by gills and then by muscle tissue. Statistical analysis (PERMANOVA) was performed to check for significant differences in δ13C and δ15N isotopic signatures between tissues and localities. The current study demonstrates significant differences in the δ13C and δ15N isotopic composition between digestive gland, muscle and gills tissues in M. galloprovincialis living in the oligotrophic environment of the Balearic Islands.