A long term survey of the P. oceanica meadow has been in progress since 1975 in the Revallata Bay (Corsica, France) (e.g. Bay, 1984). Actually, since 1991, biometric parameters of the meadow have been monitored regularly (Gobert et al., 1995). The seasonal, interannual and long term changes of these Posidonia characteristics are analysed regarding meteorological (e.g. sun, rain, temperature..) and anthropologic events such as tourism and nutrient enriched effluents in the area. Our results have pointed out the good health status of the meadow in spite of some ecological modifications linked to the increasing water temperature (Gobert et al., in press). Recent aerial photos have shown a modification of the covering surface of the meadow. An accurate study of causes of the distribution modifications is beginning. Using our long term background data on the meadow, we are developing a transplantation technique of P. oceanica shoots using semi-artificial substrates (EAT: electrochemical accretion technology) (Van Treeck and Schuhmacher, 1998) with the aim of providing a guideline-report based on model case studies representative for many threatened Mediterranean areas.