This is a bit of a difficult topic for me to conceptualize... For me, the ocean is nothing more than another body of water, which means that all of the energies associated with it are controlled by the Undines. Yet... at the same time the energy given off by the immense variety of species living in it is nothing to be scoffed at, but I don't think that energy can be safely harnessed.
The best I can relate to this is in saying that I have reached a point of trust with Undines, and any body of water is friendly towards me, no matter how immense it is. That doesn't count as "sea" or "ocean" magic specifically though.
I don't use the ocean, as I live nowhere near it, but I do incorporate the idea of water spirits, streams, creeks, rivers, lakes, ponds, etc into my work. I do this partially because "Sea" is a piece of my name, and partially because where I live there are so many lakes, ponds, and creeks.
I use the symbolism of it washing things away a lot, since I deal with a lot of emotional baggage, I like to sometimes think I can just dump it into the creek and have it carried away.
When I'm at the beach, or something, I'll write runes and sigils in the sand, I'll collect stones that have absorbed the lake's energies, and I might draw energy from the lake that I'm at.