Those croceas seem to really like jumping off the rock. What kind of light do you have btw ?
Out of four, I have one that attached and stayed on the rock. So I just left them alone. They ended up attaching to bits and pieces of rubble in the sand. The hazard with them jumping is they can injure themselves on coral.
I DO have a turbo that has developed a taste for clam, believe it or not. I had a hippopus clam that seemed to always have hair algae on it, so I introduced a few turbos. There was one that stayed with that clam long after the hair algae was gone and I thought nothing of it. One AM the clam was completely empty and the turbo was inside. I thought nothing of it (and I'm sure he had some help cleaning up the remains) but I wondered why out of eight clams that one had died?
The next night I caught that turbo on another clam and just to be on the safe side, took him out and threw him in the back tank.
Weeks later, having forgotten the incident, I moved him back to the main tank with some other astreas etc from the back. Within minutes he was on a clam shell.
Seemed bizarre to me, but he can't go back in that tank anymore just in case. The other turbos are fine and have never caused a problem.
If something was aggravating the clam at all, they may have just succumbed to the addictive taste of clam slime.