Long term changes of seagrass (Posidonia oceanica) meadows in Formentera Island due to sewage discharges and climatic forcing

[eng] Seagrasses form a key ecosystem in the littoral zone; Posidonia oceanica is the dominant seagrass species in the Mediterranean Sea. This species is threatened by human activities (including climate change) and its abundance has declined in several localities. In Formentera, Spain, the pipeline outflow of Sant Francesc water treatment plant discharges treated sewage on a P. oceanica meadow. The aim of this study is to evaluate the effect of major threats (except anchoring) to P. oceanica meadows in Formentera: wastewater discharge from Sant Francesc water treatment plant into la Savina coastal waters, global warming and storms. To estimate the effect, several parameters are being used like sedimentation rates of nutrients, vertical growth and nutrient percentage in leaves and sediment. The results show a decline in the meadows close to the sewage emission with higher mortality rates and influenced by higher sedimentation