The use of lepidochronology as a tool of analysis of dynamic features in the seagrass Posidonia oceanica of the Adriatic Sea

The lepidochronological technique was used for estimating leaf and rhizome production and for detecting past flowerings of the seagrass Posidonia oceanica of the Adriatic Sea. Samples were collected during 1997 at shallow stands (6.5-8 m depth) at Otranto (Southern Adriatic Sea) and S. Domino (Tremiti Archipelago, Central Adriatic Sea). Leaf production was estimated for the current year at Otranto and for a total of four years (the current and three previous years) at S. Domino based on the conservation of leaf sheaths. Other dynamic features (i. e. leaf formation rate, rhizome elongation and production, and flowering) were estimated for a total of 12 years (the current year and 11 previous years) both at Otranto and S. Domino. Leaf production was 574 g DW m(-2) year(-1) at Otranto and varied from 509 to 587 g DW m(-2) year(-1) at S. Domino. Rhizome elongation varied from 0.5 to 1.3 cm year(-1) at Otranto and from 0.5 to 0.8 cm year(-1) at S. Domino, while rhizome production ranged from 13 to 70 g DW m(-2) year(-1) at Otranto and from 13 to 40 g DW m(-2) year(-1) at S. Domino. A significantly lower leaf formation rate was observed at Otranto in 1996, while this parameter did not show significant differences among years at S. Domino. Rhizome elongation and production differed among years at both sites, the two more recent years (1996-1997) accounting for lower values. The data concerning leaf production at Otranto and S. Domino meadows were comparable, whereas differences between sites were observed both in the leaf formation rate and in the rhizome growth. No flowerings were observed at Otranto, while a single floral stalk deriving from a flowering which occurred in autumn 1994, was recorded from the shoots taken at S. Domino. This suggests a low frequency of sexual reproduction of P. oceanica along the Italian coasts of the Adriatic Sea. Finally, we discuss the advantages and technical constraints undergone in the use of lepidochronology. This technique, in fact, was very suitable for estimating the annual variation of the leaf formation rate, rhizome elongation and production, whereas it showed a different efficiency in the estimation of the leaf production of previous years, due to the 'status' of the plant and the general features of the bed.