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Mediterranean seagrass (Posidonia oceanica) loss between 1842 and 2009


We compiled published data in peer-review articles and grey literature reports, which we appended with our own data, to assess the changes in areal extent, cover and shoot density that Poceanica meadows have experienced between years 1842 and 2009 in the Mediterranean basin. Our results demonstrate an overall tendency towards decline of the areal extent, cover and shoot density of Poceanica meadows during the last 50 years, the period with the largest availability of records. Available estimates indicated that between 13% and 50% of seagrass areal extent of Poceanica in the Mediterranean basin appear to be lost, and that the remaining meadows of the Mediterranean may have thinned shoot density by 50% for the last 20 years and have became more fragmented. Considering the changes quantified in Poceanica areal extent, cover and density, about 6.9% of the potential Poceanica vegetation would have been lost annually over the last 50 years. The loss of Poceanica meadows in the Mediterranean may have lead to a substantial (between 11% and 52%) reduction of the capacity of this key coastal ecosystem to sequester carbon in the last 50 years, hence reducing the carbon sink capacity of the entire Mediterranean Sea. The major causes of Poceanica loss were widespread local disturbances, but recently, global disturbances, such as climate change and the spread of invasive exotic species, were also seriously threatening Posidonia meadows in the Mediterranean. These findings urgently call for implementation of management measures aiming at mitigating coastal deterioration by combining local and global actions.

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