I had the same question last month, I was cautioned that it was a hit and miss with the emarald crabs, but they are safe with reefs.
I saw mine puncturing the bubble and devour a few bubbles the very next day, but I did not see the algae population go down.
Everytime I get a chance to dip my hand in the tank, I scrap of a portion the bubble algea that is visible, and I later siphon the debri that settles to the bottom. I wear gloves as I have a couple of 8" bristle worms in my tank.
HTH
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