Just a general thought on our ocean biotopes ... they can be a violent place.
Just tonight in my aquarium I witnessed two things:
• One of our 'Dwarf Blue Leg Hermit Crabs' must have wanted the shell of our 'Scarlet Reef Hermit Crab' as he had him flipped on his back and was going at him. I made the mistake of interfering with nature and separated the two and he went right back at him literally 'head-butting' the Scarlet with his shell. I made the mistake again and put them at opposite ends of the tank but have told myself to let nature take it's course. I think the Scarlet is hurt as he is not moving now.
• Second thing I witnessed was one of our Turbo Snails was slowly creeping up the tube of our 'Feather Duster' ... I thought, no big deal, he's just eating algea on the dusters tube - well, when he reached the top of the tube near the base of the crown, he started violently shaking his shell as if he was trying to break the parchment tube to harm the worm. Again I interfered and moved the snail.
I guess the idea of a community tank doesn't necessarily exist in SW
quiet the way it does in FW