The enjambment that we keep getting between the stanzas moves us along as readers. In that way it mimics the continual motion of the waves, propelling us forward.
So what are those shafts of light illuminating? Well, we have more ambiguity here so we can't say for sure, but since those "bodies" are in the sea, we're guessing we've got more sea creatures.
Usually the word "bodies" is used to describe (usually dead) people, so again we may have more ideas here related to life and death in a people sense. Maybe we also have an allusion to the wartime dead again. Let's keep reading…
[…] The water drives a wedge of iron through the iron edge of the cliff; whereupon the stars,
Okay, so by line 20 we notice that we're no longer under the sea, chilling with the fish. We're now looking at a cliff that's being pummeled by the water.
So the ocean isn't just about those "turquoise bodies" and "shafts of light" anymore. Moore is dissolving things again by moving us out of the light and water language and into this more rigid "iron" language.
Notice Moore's choice of language here (that's called diction in the poetry biz): "wedge," "iron" (twice), and "cliff." What comes to mind when you think of these words? Besides violence, maybe there's something cold, indifferent, and even dangerous when you think of being on the "edge" of a cliff. Also, by repeating "iron" twice, the speaker emphasizes the power, inflexibility, and indifference of the water as it pummels the cliff.
At the same time, the cliff also has an "iron edge" to it. Both elements of nature, then, are rigid, cold, and in conflict.
That idea of interconnectedness pops up again, then. It's as if the sea and cliff are locked in combat here, eternally clashing like a battle between two Mother Nature's heavyweights, where the water meets the rock.
Then another natural element enters into the scene: the stars. It's as if the camera is panning upward here, first underwater, then at wave-cliff level, and now upward into the sky.
And these stars… well, they must be up to something. "Whereupon" just means right after something, so just as the water and cliff duke it out, the stars—stanza break. Let's read on to find out what they get up to…