What is it about water that it is able to dissolve even the most stubborn solid, to wash away centuries of human evolution and civilized construction? Everything comes out in this wash. Yes, we're under the oaks, but these oaks are bearded and transformed by the shifting light and the imagination of the poet into an underworld scene—the better to commune with the oneness of eternity. You can't go to eternity keeping your old form, your solid separateness, can you? Just as you need to lose some of yourself to merge with another, if you're heading into the big timelessness, you may have to enter the tide to dissolve those barriers first.
Line 1: You wouldn't think of trees as being very subtle, but these are. In fact, they are so "subtle" as to be "marine." Hmm—what would be the lovechild of these two words? We're gonna say "sublime." And that's not far from the truth of what the adjectives in this line combine to form, giving us a feeling of awe and tranquility.
Lines 2-3: The trees are marine and so is the layered light, swimming above them. Imagine a watercolor landscape, then tip over the water glass and let all the colors swim together. That's the imagery this poem creates, everything awash.
Lines 7-8: What would the ocean floor be without kelp? The grasses too are seen as part of the "marine scene." These "satisfy" the air's movements—that is, they respond to them, and give them purpose in their fluid response.
Lines 10-12: Even the lovers are constructed of sea-stuff. Polyps are a kind of coral and, if they colonize, they'll create just the kind of atoll the poem mentions—that is, in something like 200 million years. Have these two really been lying there that long, or does it just feel like it? It seems like under the spell of this Octopus' garden, time feels like it does extend backwards and forwards into a kind of infinity.