Urchin shedding and replacing spines
 

I know that mostly when urchins start loosing spines it's a sign they're stressed, but do they also shed and replace them gradually?
Reason I ask is that my rock boring urchin has lost a few but has new ones to replace them, only about four five though. I checked nitrate as I heard they don't tolerate that well, result was zero.
Since changing my rock there's no coralline which seemed to be his favourite but there's plenty of algae so he shouldn't be starving, though he has been hunting down and forcibly cleaning the coralline off my snails...
Should I be worried?


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Nah it's probably fine. My urchin did the same thing when I move him from one tank to another.

Thanks, that's good to know. He's kind of a favourite.


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Urchin
 

My long spine lost almost all of his when I purchased it. 4 months later its spines are a good 6 inches.