The pools were filled with doliolids!
Here's a close-up showing how dense they were:
And another shot, with some of the doliolids floating at the surface. You can see their barrel-shape, with prominent muscle bands:
I don't recall seeing abundances and concentrations of doliolids in the intertidal zone like this before. For the record, here are a few more examples:
Draped over Feather Boa Kelp (Egregia menziesii)
Undigestible portions being spit out by Aggregating Anemones (Anthopleura elegantissima) — the large pinkish blobs emerging from the anemones' mouths:
There were so many doliolids, they were painting the waves purple!
I introduced doliolids last year, so to learn more about them, read the post from 15 June 2015.
P.S. I heard that doliolids were also seen at Doran Beach today. If you come across them, let me know — it would be fun to know where else they're showing up.