Halloween hermit carving into reef rock?

[taylormaximus]

So I just bought a Halloween hermit crab a couple days ago, and it's been doing fine, but I just came home today to find it carving into the reef rock? Like actually breaking chunks of the rock off and exposing the bare white...

You can see here the big white patch compared with the colour of the rest of the rock, and some of the rubble falling below. (the crab isn't in the picture as I pulled it off as soon as I saw what was happening).

Has anybody heard of or seen this behaviour??? Or why it's doing that? Honestly I didn't think they were strong enough to break reef rock. But also this is a big problem because it looks awful. If it starts doing it again I think it'll be back to the fish store for him. :(

 

[Timfish]

Yup, it's doing what it's supposed to do. They're algae eaters and will scrap algae off rocks. Depending on how porous the rock is and the effect endoliths and biofilms have on dissolving the rocks some of the rock may come off also. Beneficial process in my book.