Fighting Conch Making Circles in Sand

[LJLKRL05]

I have two fighting conchs, and since I have had them they make these circles in the sand bed. They are about 3 inches across and raised. I have watched them do this, so I know it is them making the circles.
Any ideas what they are doing?
These pictures are from this morning before the lights came on.

 

[nautical_nathaniel]

They probably found some good stuff to eat in that spot and wanted to make sure they got it all.