Can hermit crabs live in the ocean?

Yes it can but it depends what kind of shell. The shell must be like a conch shell, but not the kind for snails. There would be not enough room for the crab to squeeze his body in. You need a shell with an opening a little bit bigger than the shell opening it already has on if you want it to change into the new shell. But most the time they do not change shells (I have had one for over a year and it still hasn't). I know you probably want it to change into the pretty new shell you bought or found but do not try to manually do it for the crab.