FATE OF PRIMARY PRODUCTION IN POSIDONIA-OCEANICA MEADOWS OF THE MEDITERRANEAN

Primary production of Posidonia oceanica meadows was estimated at two sites in the Mediterranean basin (Marseilles, France and Ischia, Italy ), in the 10 to 20 metre depth range, At the five stations studied, fo liar production (blade + sheath) ranged from 67.7 to 146.6 g C m(-2) y r(-1) and rhizome production from 8.2 to 18.0 g C m(-2) yr(-1). Based on litter input (rhythm of fall of leaves), stocks (biomass) and kinet ics of litter decomposition, the rate of export of this necromass was estimated. The rate of export was strongly influenced by depth and hyd rodynamic forces which ranged from 51 to 68% at Marseilles (stations e xposed to strong currents) and from 37 to 49% at Ischia, Exclosures at Marseilles were used to assess the proportion of the foliar productio n consumed by macro-herbivores in this area. The values recorded range d from 24.8 to 35.3 C m(-2) yr(-1), of which 44% is absorbed. On the b asis of all these results, the fate of stocks and the flux of elements resulting from primary production were determined. For the Marseilles stations, carbon followed four major pathways: 10% was consumed by he rbivores, 23% was decomposed in situ as the result of detritivore acti on, 35% was exported in the form of litter and 32% was stored in the m atte (sheaths and rhizomes). For Ischia, the values were 3%, 34%, 27% and 36%, respectively. Extrapolation for the whole Mediterranean gave an estimated total production of P. oceanica meadows of 3.5 million to ns of carbon, of which 2.4 million tons are lost to the community thro ugh export or storage in the mat. (C) 1997 Elsevier Science B.V.