δ13C and δ15N variability in Posidonia oceanica associated with seasonality and plant fraction

The carbon and nitrogen isotopic compositions of fractions of the seagrass Posidonia oceanica (L.) Delile in a Mediterranean shallow environment (Stagnone di Marsala, western Sicily) were investigated seasonally throughout 1998. The stable isotope ratios of seagrass leaves (intermediate and adult), rhizomes, leaf litter and aegagropiles were compared over 1 year in order to distinguish between seasonal and plant part variability. Significant differences in the isotopic composition tested using ANOVA were observed as a function of both plant fraction and season. There was an overall trend towards less discrimination against 13C in summer (average δ13C ∼ -10‰) than in winter (average δ13C ∼ -…