Not much of the ocean related mod out there, don't you think?
Feel like the ocean should be a place to get more things to explore under water or to be able to dive even deeper down.
Upgrade Aquatic - This one is great so far.
Underwater Biome - Subnautica in a nutshell, still got a lot more to go.
And 1 or 2 more which they're not yet to update.