First, that's an incredibly beautiful, and masterful, photograph!
OK, they're rocks.
I don't want to dwell on them, but I have been wondering why I thought they might be breaking waves.
The visual clues in the reference to them being rocks are:
They have broken, soft, or indistinct bottom edges. They suggest they're in water or partially buried.
They have super-sharp sides and tops, so we know they are separate from their background.
They have subtle three-dimensional shaping. So they have mass and form.
Now, in your drawing, they have highlights on top that suggest breaking waves. Their values are solid and dark, suggesting shade rather than three-dimensional forms. And... If you work out WHY the rocks look like rocks, you can repeat the same in your drawing - in any way you want to - and you'll achieve the same visual result.
Does it matter that I read the dark shapes as being the insides of waves, rather than static rocks? Certainly not. It remains a lovely and emotive drawing. But it's also a good exercise in extracting visual clues.
Just lately, I've been thinking about writing a second book - on Visual Clues. And a few other associated ideas... like avoiding optical illusions. Hmmmmm....