@SomeoneElse, 
I'm sorry that the revert turns out complicated. Yes, some of the seagrass, that has been there since long and which is not part of this changeset #137667141 has been deleted completely, too. However, I can certainly say that minor amendments to this preexisting seagrass have all been committed as minor changeset before the changeset #137667141. 

For theses minor changes, we should now look for the revert of the revert. I can further assure that these were all the seagrass around the islands of Ios, Iraklia and west side of Shinousa. This seagrass, carefully manually mapped from bing, maxar, Esri and Mapbox as well as by diving in some of the areas are now lost. 

Can you identify this by the exact timing of the changesets before and after changeset #137667141? 

This would be the correct and precise solution to this revert complication.

If you tell me 'how to' I am happy to help this necessary sorting process.

Jo