I’m not sure if cracks on the body portion of a crab’s shell would be fatal or not, or if it would depend on severity. Maybe @Jay Hemdal would know?when I got home he had a crack in his shell and he is very sluggish, can I heal him?
If it’s not fatal, then I’d assume it would heal over the course of a (few) molt(s) for the crab as long as the crab has enough good food and living conditions.