The epiphyte load, the ash content of the epiphytes, the leaf biomass, the nitrogen and phosphorus content of the leaves, and the density of shoots of the Mediterranean seagrass Posidonia oceanica (L.) Delile were monitored yearly from 2003 to 2008 in two shallow meadows off Mallorca (western Mediterranean) with the aim of identifying the responses of P. oceanica meadows to mid-term environmental variability. Inter-annual variability of P. oceanica meadows was significant for most of the descriptors examined: shoot biomass, epiphyte load, nitrogen and phosphorus content of the leaves, and shoot density. Shoot density increased by a factor of 2 and epiphyte load by a factor of 4 from 2003 to 2008. P. oceanica descriptors were generally not correlated with each other or with the average sea surface temperature during August. Long-term data series of descriptors of P. oceanica status are essential to improve understanding about the response of this important Mediterranean coastal ecosystem to natural and anthropogenic disturbances and to assess the effects of rapid global environmental change.