The last half year, the GIS-team was working out a method for seagrass mapping. Global seagrass meadows are under threat. Reduction of water clarity, climate change and dredging destroy meadows at an incredible speed of 1.5% a year. The mapping of the Greek seagrass meadows, especially the specie Posidonia Oceanica, remains behind and counteracts conservation purposes. 92% of the Greek coast needs to be mapped promptly but accurately in the near future. The teams developed several mapping methods for Posidonia Oceanica. The GIS-team was working on the satellite imagery mapping. For the first time, a combination of sonar and drone field data was used as training data for the satellite image classification. The results for Lipsi, Southeast Aegean Sea demonstrate large seagrass meadows on the gentle slopes and no meadows on the steep slopes. With an accuracy of 77% are the results reliable.

The research discovered more revealing results. The positioning of the seagrass meadows is related to the island evolution since the last 21 kyr (Last Glacial Maximum). Paleo-climatological conditions showed the past distribution and possible formation of an ecological corridor for the last 21 kyr. This research shows up, that the meadows in the SE-Aegean Sea are under a more intensive threat. The location on the Anatolian shelf creates a shallow enclosed sea where the sea surface temperatures are too high for Posidonia Oceanica. This will influence negative the distribution of Posidonia Oceanica in the near future

The main function of seagrass meadows are ecological and food supply services. In the SE-Aegean Sea the Posidonia Oceanica meadows are the major carbon stock source. The report of the GIS-team addresses the problems facing Posidonia Oceanica in the SE-Aegean Sea. Urgent mapping and conservation is necessary to conserve important habitats for anthropogenic influences.

Tim Grandjean, University of Amsterdam