I just watched one of my black longspine urchins that I've had for about 4 months now eat a track up one of my $80 ORA Acro frags and crawl back down. This would explain why 2 of my other Acros look like somebody has scraped flesh/skeleton off with a potato peeler. Has anybody else seen this happen? I have recently started scrubbing and blading all of the algae in my tank to encourage these algae-eating machines to turn their hunger on the coralline that is starting to get out of hand. Has anybody heard of them doing this before when they're out of non-calcaerous algae? I've had them for 4 months and they've never once damaged a coral until the last few weeks! Only sps as well (not including my Hydnophora, but I think they'd have to have a cast iron stomachs to eat a Hydnophora).