The Bible says that God created our Sun and the stars. We look out into the universe and see that Stars are in the process of being created by gravity and nuclear fusion; this in now way entails that God is not creating THESE stars as well.
The “command” that God gave the Oceans needn’t be any more mystical than the means used to create the stars.
I've been pointing this out lately in a few different threads. Note that fowl are brought forth from the waters along with great whales and "every living thing that moveth" on day 5.
"Fish gotta swim and birds gotta fly ... I think that's interesting, don't you?"