Small green mushroom looking things?

[MikeC]

Can anyone identify ?
To me these look like small green toadstools/mushrooms
Not bubble alge as they have stalks and are not shiny like bubble algi.

 

[skene]

caulerpa nummularia

 

[fishman1069]

+1 grape caulerpa, very invasive and hard to get rid of

 

[MikeC]

+1 grape caulerpa, very invasive and hard to get rid of

Great! Any sudjestions on how to? I should be able to take the rock out if need be to work on.