Seed nutrient content and nutritional status of Posidonia oceanica seedlings in the northwestern Mediterranean Sea

We studied nutritional constraints on growth of Posidonia oceanica seedlings, morphometry and elemental content of mature seeds, and seedlings stranded on a beach of the northwestern Mediterranean Sea on 3 dates (May 2004, May 2005 and December 2005). The mean total nitrogen (N) and phosphorus (P) content of P. oceanica seeds was high compared with closely related species, Seeds varied considerably in mass, and their nutrient and carbon (C) content. increased linearly with mass. This indicates substantial variation in the amount of reserves initially available for seedling growth. Stored reserves in seeds were used by seedlings within 6 to 8 mo after germination: P was retrieved with greater efficiency (86%) than was N (69%) and C (20%). From May to December of the 2nd year (2005), the tissue nutrient concentrations of seedlings declined due to fast utilization and translocation of nutrients from the internal pools to support summer growth. Instead the C concentration in roots and rhizomes increased, indicating an accumulation of C. Seedling tissue N and P concentrations were above the critical levels reported for seagrasses, and were also lower than those of plagiotropic rhizomes of P. oceanica collected in the same period. These results suggest that P may play a major role in constraining growth of P. oceanica seedlings.