That said, there are also reports like the one linked below where the crabs
may be responsible for killing coral colonies.
https://link.springer.com/article/10.1007/s00338-010-0654-x However, the corals dying may have been caused by a few separate things:
-Overpopulation of crabs
-Disease
-Bleaching
-Etc.
If the corals were dying for reasons unrelated to the crabs, however, then the crabs may have been trying to protect the healthy colonies by consuming the sick/dying ones.
So, the crab is essentially typically a beneficial parasite; if the coral is small or struggling in your tank, then the crab could very well kill it, but if it's large and doing well, it should be fine to keep.
