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.) De lile was examined in 5 meadows in NE Spain to assess the relative impo rtance of large-scale versus local factors in controlling the seasonal patterns observed. Large-scale seasonal forcing, resulting from chang es in light and temperature associated with the solar cycle, was asses sed from the coherence of seasonal growth patterns among the meadows a nd accounted for 46 and 43% of variability in shoot size and growth, r espectively. The local component of seasonality, which results from lo cal variation in environmental variables (e.g. nutrients, dissolved in organic carbon, redox potential) was assessed as the differences in th e annual time course of shoot size and growth among the meadows, and a ccounted for 9 and 12% of the variability, respectively. These results support the contention that seagrass seasonality is primarily control led by the solar cycle, and secondarily by seasonal changes in the env ironment which are at least 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 corre lations between such variables and seagrass growth.