The gulls know, but they're not telling
January 28, 2019 5:21 PM   Subscribe

What are these things? The outsides are like thick leather; the insides are viscous red liquid. Gulls bring them in from the ocean, drop them on the beach, poke them until they deflate, and eat them.

For the last two winters, along Pacific Beach in San Diego, we've seen a lot of gulls eating the things. They look like some kind of egg, or maybe sea creature, but I can't find anything online even close.

The things are reddish-brown, sphere to ovoid-shaped, walnut to golfball-sized, with fibrous, leathery shells and viscous red liquid inside.

The gulls bring them in from the water, maybe 50-100 yards from the shore. We've never seen one wash up on the beach by itself, and the gulls aren't digging them up.

The gulls drop them on the beach, and then poke them with their beaks until they puncture and deflate. Thick red liquid squirts or runs out, then the gulls swallow the skins and the insides.

The outside has enough fibrous stuff that sometimes the gulls will pick them up by the fiber.

The gulls like them a lot, and sometimes fight over them.

They're only around for a week or two in the winter, though they may also be back other times of the year (we're only here January-February). When they're around, there are a lot of them, and it seems like more gulls are on the beach when the things are available.

The only birds we've seen eating them are Western and Ring-Billed Gulls.

Any ideas? I've googled everything I can think of, and am not coming up with anything useful.
posted by still_wears_a_hat to Science & Nature (6 answers total) 5 users marked this as a favorite
Sweet Potato Sea Cucumber? (I found it on iNaturalist, which is a totally killer app)
posted by RobotVoodooPower at 5:34 PM on January 28, 2019 [4 favorites]

That is a tunicate. I don't know what kind of tunicate, but it is one. One end of it should be anchored to a substrate, the other is its orifice. They are neat because they are technically chordates, placing them in the same phylum as humans.
posted by Anticipation Of A New Lover's Arrival, The at 5:35 PM on January 28, 2019 [3 favorites]

Ooh, or maybe I was very confidently wrong. I also ran that through iNaturalist but got nothing!
posted by Anticipation Of A New Lover's Arrival, The at 5:36 PM on January 28, 2019 [1 favorite]

Heh, iNaturalist was where I went immediately as well. Here's an observation that looks a lot like yours, seagull included.
posted by bethnull at 5:39 PM on January 28, 2019 [4 favorites]

2nd tunicate of some sort- aka sea squirt. Cool little animals.
posted by Patapsco Mike at 5:39 PM on January 28, 2019 [2 favorites]

Thanks, everyone, that was driving me nuts. I'm pretty sure it's a Sweet Potato Sea Cucumber, and also pretty sure I wouldn't have found it myself.
posted by still_wears_a_hat at 3:03 PM on January 29, 2019

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