Urchins
 

Quick question. Why would an urchin release a white fluid from the top of itself, and what could it be? Stress response or something? Should I be concerned?

well, for one they pooh from there but i believe that it may be spawning if it's not pooping...neat trick huh?

http://www.oceanlight.com/spotlight.php?img=05346

look familiar?

No, it's not stressed per se - it's horny. The release of white stuff is a breeding response. I've noticed it happening once in a while if there's a localized change in salinity such as when top-up water is poured into an area where the urchin is. Shouldn't be a big deal unless you've got a small tank in which case a water change and perhaps running some carbon would be an easy fix.