Flowering of the seagrass Posidonia oceanica in the NW Mediterranean: Is there a link with solar activity?

Time series analysis of the leaf biometry and rhizome production of the endemic Mediterranean seagrass Posidonia oceanica (L.) Delile was performed for a meadow in the Ligurian Sea (NW Mediterranean) in order to assess changes in plant growth during a massive flowering event that occurred in 2003 and coincided with the warmest summer temperatures recorded in the last centuries. P. oceanica exhibited the highest values of leaf surface area during the flowering year and the highest values of rhizome production in the previous year. The years immediately following the flowering event were characterized by a decrease in both parameters. Comparison of the years of massive flowering events reported in the literature for the entire Mediterranean with the historical series (spanning the last 50 years) of air temperature and sunspot number suggests that intense solar activity, and not warmer temperature per se, is likely to be the main trigger of massive Posidonia oceanica flowering events.