PRIMARY PRODUCTION OF POSIDONIA-OCEANICA IN THE MEDITERRANEAN BASIN

Primary production of the marine phanerogam Posidonia oceanica (Linnae us) Delile was measured by lepidochronological analyses at 22 sites in the Mediterranean Sea (Corsica, France, Italy, Sardinia and Turkey), between 1983 and 1992, to determine spatial and temporal variations. L eaf production (blade and sheath) ranged from 310 to 1 540 mg dry wt s hoot(-1) yr(-1), depending on site and depth. Rhizome production range d from 24 to 120 mg dry wt shoot(-1) yr(-1) (6% of average leaf produc tion). At some sites the results obtained by lepidochronological analy sis were consistent with earlier results obtained by classic methods ( e.g. leaf-marking). While primary production per shoot (mg dry wt shoo t(-1) yr(-1)) displayed no significant differences between sites, prim ary production of the P. oceanica meadow (g dry wt m(-2) yr(-1)) decre ased with increasing depth at all sites studied. This decrease correla ted with reduced density of the meadow (number of shoots per m(2)) wit h increasing depth. Past primary production was also extrapolated at t hree sites at the island of Ischia (Italy) for a period of 5 yr in ord er to determine interannual variations over a period of several years. While major variations were recorded for the surface stations (5 and 10 m depth), production remained stable at the deepest station (20 m d epth). Given the large geographical scale of the study (location, dept h range), it would appear that while P. oceanica production remains co nsiderable, the values recorded in the literature on the basis of clas sical analyses (surface stations) represent maxima, and cannot be gene ralised for meadows as a whole.