Pincushion urchin eating coralline algae

I have a pincushion urchin and I think it is eating my coraline algae. Is that normal? I first noticed it yesterday when I noticed that the rock piece that the coral is on was missing a lot of coraline and then I found scratch marks on my rocks in the pattern that its mouth would have made. I should have investigated more when it kept getting on the coral and knocking it over.

The fist pic is of the base rock before and the second one is how it looks now and the third one is the scratch marks.

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