I wouldn't trust them in a reef environment. Maybe when they're very young they might be ok. Once they start to grow they're going to see your shrimp and crab as meals. Plus, coris wrasses tend to like sand beds to sleep in. Can make a mess as they make and unmake their beds each day. For a reef I'd go with one of the fairy wrasses. Plenty to choose from and they're all beautiful IMHO.