There are some types of anemones that like to hide beneath your rockwork but I have never seen one like that before...
I'd also go with egg mass, if it was me id take it out and put it in a small holding tank until they hatch to find out what they are.
Are they round solid balls or is it some type of tubing or respiratory system surrounded by a spongy growth?
If its balls then its most likely eggs. With tunicates you will see larger out openings and smaller ones following some type of design on the white parts. There is a much more defined pattern with tunicates.
Patterned eggs
OR something more like this with distinct openings.
It still looks more like an egg mass to a few people. I would take it out and QT it to make sure since it doesn't look like any good eggs i know of or that anyone else responded to.