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 ocea nica of the Adriatic Sea. Samples were collected during 1997 at shallow sta nds (6.5-8 m depth) at Otranto (Southern Adriatic Sea) and S. Domino (Tremi ti Archipelago, Central Adriatic Sea). Leaf production was estimated for th e current year at Otranto and for a total of four years (the current and th ree 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 curr ent year and 11 previous years) both at Otranto and S. Domino. Leaf product ion 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 y ear(-1) at Otranto and from 0.5 to 0.8 cm year(-1) at S. Domino, while rhiz ome 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 form ation rate was observed at Otranto in 1996, while this parameter did not sh ow 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 betw een 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 rep roduction of P. oceanica along the Italian coasts of the Adriatic Sea. Fina lly, we discuss the advantages and technical constraints undergone in the u se of lepidochronology. This technique, in fact, was very suitable for esti mating 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.