Urchin Shrinking

[swebb]

I have had this long spine urchin for over a year now. Over the last three weeks, its spines have been getting shorter (6+ inches to around three). No spines are missing from it and I have not noticed an abnormal amount of spines in the sand. Some of the spines appear to have a small amount of filamentous algae attached. It appears to be acting normal as algae is not taking over the tank and he is still finding and eating the nori sheets I put in the tank. It also spawned on Sunday after a water change. Does anyone have any ideas on what could be causing this and is it any reason for concern? Thanks in advance.

 

[reef lover]

If the spines are deteriorating than that is not good....

 

[Bret Brinkmann]

What fish are in the tank?