Article

The study or cyclic variations of sheaths thickness (lepidochronological analysis) ofthe marine phanerogam Posidonia oceanica was carried out on orthotropic rhizomes in a coastal lagoon (Stagnone) to investigate the effects of climate changes. This study has allowed to learn information on the evolution of meadows since 1981 to 1995. P. oceanica meadow, in the study area, shows evident regression signals. Rhizomes annual mean growth, in the latest five years, shows a significative decrement, stimated around 28%. In addition, a gradual decrease of rhizomes primary production has been observed during historical series explored. The extrapolation for the whole meadow gives an estimated total rhizome production of 26,05 tons dw y^-1 in 1981 and 15,32 tons dw y -I in 1995, recording a loss of 41%. Thus, rapid decline of P. oceanica meadow indicates (hat coastal lagoons may be considered a highly vulnerable habitat where short-term climatic effects on seagrass ecosyslem are possible and where the lepidochronological parameters employed constitute a useful tool in the delinition of P. oceanica as a "biological indicator" of the environmental changes.