From my experience Emerald crabs do not do much to the bigger size bubbles. Generally when I had them I would remove them while siphoning during a water change and not worry about popping them. Once you get rid of the bigger ones the crabs do a pretty good job at keeping new ones at bay. That and rabbit fish. Also sometimes Desjardini Sailfin tangs. I currently have Emeralds and a Sailfin with no issues for several months.
Cheers