Sea-grasses are aquatic angiosperms completely adapted to live in the marine environment. The number of species is rather small, about 50, belonging to 12 genera in the order of Helobiae, 9 of them belong to Potamogetonaceae and the other 3 to Hydrochar taceae.According to our own survey, The beds of Thalassia Enhalus and Cymodocea, are distributed in the tropicol seas around the islands of Hainan and Xisha, while the beds of Zostera and Phyllospadix are widely distributed in the temperate seas of Shandong,...