Using seagrasses to identify local and large-scale trends of metals in the Mediterranean Sea

To manage trace metal pollution it is critical to determine how much temporal trends can be attributed to local or large-scale sources. We tracked changes in metal content in the seagrass Posidonia oceanica, along the NW Mediterranean from 2003 to 2010. While Cu, Cd and Ni showed a large inter-site variation, likely due to local factors, Fe, Mn and Pb showed little local variation and synchronous interannual variability across sites, most likely due to large-scale sources. Zn showed equal importance of local and large-scale sources of variation. Temporal trends of Ni, Zn, Cd, Cu remained almost stable. In contrast, Fe, Mn and Pb slightly increased in the last decade. These trends suggest that metals like Cu, Cd, Ni can be effectively managed at local scale. Whereas, elements like Fe, Mn and Pb have an important large-scale component that needs to be managed across the frontiers of national jurisdictions. [Display omitted] •Metal contamination in North-western Mediterranean coastal waters is driven by local and remote sources•Predominance of local or remote sources depends on the element•Metal contamination appeared to be almost stable from 2003 to 2010•Local but also global sources of metal pollution in coastal waters need to be considered for effective management.