Marine Metaphors

The storms have rearranged this beach,
here sand removed, there new dunes built,
driftwood restacked, a fresh high-tide line drawn
in strands of kelp and wrack. Ripples splash across
the pool where a tiny tunicate matures.
Spine, gills, tail; we know the succession of forms
till a full-blown air-breathing vertebrate
leaps walls of rock and climbs the shore alone,
while ebb-tides drain the pool.