STABLE-ISOTOPE SIGNATURES (δ13C AND δ15N) OF DIFFERENT TISSUES OF PINNA NOBILIS LINNAEUS, 1758 (BIVALVIA): ISOTOPIC VARIATIONS AMONG TISSUES AND BETWEEN SEASONS

The fan mussel Pinna nobilis is a rapidly growing suspension-feeding bivalve endemic to the Mediterranean Sea and usually inhabits seagrass meadows. This endangered bivalve assimilates carbon and nitrogen isotopic ratios in tissues from its food sources. The delta C-13 and delta N-15 signatures were used to demonstrate isotopic variation among three tissues (digestive gland, gills and muscle) and (for digestive gland and gills) between summer and winter. Isotopic values were in the order: gills approximate to muscle. digestive gland. The mean values of the isotopic signal for delta C-13 were -20.41 +/- 0.12 parts per thousand, -19.78 +/- 0.07 parts per thousand and -19.30 +/- 0.5 parts per thousand and for delta N-15 were 2.84 +/- 0.11 parts per thousand, 4.05 +/- 0.14 parts per thousand and 3.51 +/- 0.15 parts per thousand for the tissues digestive gland, gills and muscle, respectively. Seasonal variations (summer-winter) were found in the isotopic signals (delta C-13 and delta N-15) for digestive gland and gills of fan mussel. As a result, this study suggests muscle as the appropriate tissue for future trophic studies and indicates that isotopic signals should be compared in the same season. These delta C-13 and delta N-15 values are among the first available for P. nobilis and contribute to the library of delta values for marine invertebrates.