This video says about itself:
Eelgrass (Zostera marina) underwater in Ireland
Posted on October 13, 2015 by Bert Corté
Researchers from Rijkswaterstaat, Radboud University, the Field Work Company, Arcadis and the Forestry Commission last Thursday investigated a new field of eelgrass (Zostera marina) south of Rottumerplaat and Rottumeroog. This followed an earlier discovery by our birdwatchers. In a short time approximately 21 hectares of eelgrass have grown around the so-called Boschplaat. After sampling this appears to involve some 5,000 plants which have returned here spontaneously. Further genetic research must clarify what the origin of these plants is.
Our birdwatchers Bart Ebbinge and Doortje Dallmeijer this summer on Rottumerplaat saw in late July just south of the gully below the island a small field of dwarf eelgrass (Zostera noltii) which had developed quite a lot compared to 2013. About a kilometer further south, in the lee of mussel beds, they found more than 100 scattered common eelgrass plants growing. …
Common eelgrass has much broader and longer blades than dwarf eelgrass. Both types of seagrass are very important for the survival of many fish and birds in the Wadden Sea.