Acans receding - looking for suggestions on possible causes

[gregzz4]

I just pulled out the acan that is currently suffering the most as I found it in the clutches of the urchin last night and was preparing to re-glue it

I decided to remove all the old glue first and wouldn't you know it, there are worms inside the underside of the skeleton
It's currently in a dip and I'll post pics once I'm done

Hopefully this is the cause and the recession will end