10 Oysters (less)
Don't worry about the flowers at the top. They will open with the falling crops as you are moving about below them.
As you know with the oysters, you need to continually make moves next to any opened ones to avoid them closing again. But on top of this are the moving crops that are on the logs on the river.
Try to make rows in between the crops, or along them. Set up rows so that they will make new matches after the first.
Use shovels to remove oysters or crops if they are in the way.