The foam was back this morning at the lower pools. I'd gone down before the aquarium opened — low tide around 06:40, sea flat enough that the kelp wasn't thrashing — and the north-facing crevices were full of it: dense, white, not quite cream-coloured, holding its shape for what felt like minutes after the last wave had pulled back.
The question: why does that foam stay so much longer than the foam in my kitchen sink?
Both are driven by surface-active agents — molecules with a water-loving end and a water-avoiding end that line up at the air-water boundary and lower the energy cost of forming new surface area. In seawater, those agents are mostly proteins and lipids shed from phytoplankton, zooplankton, and the general biological machinery of the nearshore zone. The collective term is marine surfactants, and they're structurally heterogeneous in a way that dish soap, a single engineered molecule, is not.