Oceanic Crab Makes Landfall

Miles of monotonous sand. When I’m not concentrating on surf zone fishes and their prey, or the riches of the rocky intertidal, I’m walking the wrack line. If you look at Wrack Line 2014 or any of my Wrack Line pages, you will see examples of things that have washed up on the beach – things that caught my eye and imagination. Every one of them has a story. Wait ’til you see what made landfall on the deserted beach featured above.

Home made float
Homemade float

A few days ago, on May 31, I made a curious find. Finding a float on a lonely stretch of beach isn’t too curious, we find them all the time, but most are store-bought, like the UBE float I found nearby.

UBE float
UBE float
Pelagic goose barnacles on a homemade float.
Pelagic goose barnacles, Lepas, on a homemade float.

The homemade float had lots of handy attachment points and it’s bottom was cloaked in a colony of good-sized pelagic goose barnacles, Lepas. The barnacles were eye-catching beauties, but in the sand just beneath them I soon noticed movements and here is what I found.


There was something familiar about this little crab; it looked like our shore crabs, Hemigrapsus and Pachygrapsus. I let it crawl up my index finger, where it seemed quite at home, unlike shore crabs I have known – which are not at all at home on fingers. Pulling it off was quite the task. This crab is built to stay on.

Flotsam crab, Planes
Flotsam crab, Planes

Meet the flotsam crab, Planes major. At least I think it’s P. major, because the carapace is widest behind the eyes. If you see things differently, I’d love to hear from you. This crab looked familiar because it is a related to the shore crabs I mentioned earlier – same superfamily, Grapsoidea, if you are up on your crabs. As far as I can tell, there are three species of Planes, and they are all oceanic. A lot of people in Oregon, those that have seen them, call Planes drifter crabs, and elsewhere you may see Planes, especially P. minutus, called Columbus crabs. The screen shot below explains that.

Screen Shot 2014-06-03 at 10.13.31 AM

Planes - multiple size classes on a single float.
Planes – multiple size classes on a single float.

The float I found with its covering of pelagic goose barnacles must have been a good, you might say fertile, home for these crabs; seems there was a lot of reproducing going on. How many size classes do you see?

On Pacific Northwest beaches, flotsam crabs and maybe another drifter, Planes marinus, occasionally show up in the wrack on floats and other debris. These are the first I’ve seen. I wonder about their story, and the story of their float and the people who built and deployed it.

This isn’t the first new oceanic species I’ve written about this spring. In An Oceanic Predator Washes onto the Beach, I wrote about the lancetfish, a fish rarely observed on shore, or anywhere.

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