Annual growth dynamics of Posidonia oceanica:contribution of large-scale versus local factors to seasonality

The seasonal growth pattern of the seagrass Posidonia oceanica (L.) Delile was examined in 5 meadows in NE Spain to assess the relative importance of large-scale versus local factors in controbng the seasonal patterns observed. Large-scale seasonal forcing, resulting from changes in light and temperature associated with the solar cycle, was assessed from the coherence of seasonal growth palterns among the meadows and accounted for 46 and 43% of variability in shoot size and growth, respectively. The local component of seasonality, which results from local variation in environmental variables (e.g. nutrients, dissolved inorganic carbon, redox potential) was assessed as the differences in the annual time course of shoot size and growth among the meadows, and accounted for 9 and 1 2 % of the variability, respectively. These results support the contention that seagrass seasonality is primarily controlled by the solar cycle, and secondarily by seasonal changes in the environment which are at leas1 in part caused by the temporal variability of seagrass growth. This indirect link between light and temperature and local conditions needs to be taken into account to interpret correlations between such variables and seagrass growth.