It seemed worthwhile to confirm the identity of these animals, so I took a quick look today. Sure enough, quite a few innkeeper worms (Urechis caupo), also known as spoon worms (echiurans), were washing up on the outside of Doran Beach (the bay side, not the harbor side), fairly close to the North Jetty.
Here are a few documentary photos of the gulls (primarily Western Gulls) taking advantage of a food resource not often available to them:
And here's a close-up of an innkeeper worm washed up on the sand, before a gull encountered it:
This innkeeper worm was not in its best form — that is, they normally live in U-shaped burrows in the mud, and I'm guessing it had been out of its burrow for while and that its condition had deteriorated while washing around in the surf. But you can still see a few important characteristics — the pink coloration, the sausage-like shape, and the golden setae (bristles) at both ends. The ring of bristles at the posterior (back) end are quite prominent in good light, while the two bristles at the anterior (front) end are harder to see.
Perhaps you're wondering about why they're called innkeeper worms? I mentioned they live in U-shaped burrows. A few other animals are resident alongside the innkeeper worms in their burrows — see diagram below:
From Fisher, W.K. and G.E. MacGinitie. 1928. The natural history of an echiuroid worm (Urechis). Ann. Mag. Nat. Hist. 10: 204-213. (a) innkeeper worm, (b) scale worm, (c) pea crab, (d) goby.
So the remaining question with this current observation is: Why are the innkeeper worms washing up on the outside of Doran Beach?
Have you seen this phenomenon before? Do you have ideas about what could be happening?
As far as I know, most of the innkeeper worms live on the mudflats in Bodega Harbor. Do some of them live on the outer coast? Or, were they somehow flushed from their burrows in the harbor and then washed around to the bay side and concentrated near the jetty? If so, how did this happen? Could it have been related to the storms last weekend? Did the heavy rain cause channel scouring that removed some innkeeper worms from their burrows? It is possible they were impacted by fresh water?
Lots to wonder about. Let me know if you can think of other scenarios that would concentrate innkeeper worms in this way.