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Unusual Mole Crab Incident Reminder Oregon Coast is Full of the Unexpected

Published 08/04/22 at 5:45 PM PST
By Oregon Coast Beach Connection staff

Unusual Mole Crab Incident Reminder Oregon Coast is Full of the Unexpected

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(Seaside, Oregon) – One thing that the Oregon coast is consistent for is the unexpected – the surprises and twists 'n turns of what happens at the tideline. (All photos courtesy Seaside Aquarium)

Case in point: one natural event a few years back had some people scratching their heads initially. One winter in 2017 found a whole hoard of mole crabs apparently dead at the tideline. Tiffany Boothe of Seaside Aquarium made the discovery while beachcombing, given her pause. Lots of dead mole crabs appeared to litter the shoreline, half submerged in the sand where they usually live.

There was a big cold snap at the time – it was the end of January, after all. So maybe they were just cold-stunned?

Indeed, the oddity had at least one state expert saying he'd never seen this before.

“Most of these seemingly dead mole crabs were simply cold-stunned,” Boothe said. “The outside air temperature had been much, much cooler than the local ocean temperature (with local air temperatures around 28-34 F and ocean temperatures around 48-50 F). These poor little crabs, when uprooted by heavy surf and stranded on the beach, got too cold to burrow down into the sand.”

That Mystery a Few Years Back of 'Dead' Mole Crabs on N. Oregon Coast

She said it was likely the mole crabs were revived sometime after. In the meantime, they were literally frozen in time: they normally live under the sand but were partially out, as if they were trying to wriggle out of their sandy residence when they froze.

Oregon Coast Beach Connection contacted Scott Marion, Marine Habitat Project Leader, with Oregon Department of Fish and Wildlife (ODFW) at the time. He had not heard of anything like this before, but it didn't entirely surprise him, either.

Mole crabs inhabit what is called the swash zone, he said – an area that is extremely important to near-shore environments. It's a narrow stretch that sits just beyond the tideline.

“Mole crabs' general behavior is to ride the waves into the swash zone, and they forage in the sand there and quickly bury,” Marion told Oregon Coast Beach Connection at the time. “So I can imagine if you had a combination of really big waves carrying them far up the beach and very cold temperatures that they would be slower to get buried quickly.”

Boothe said it's likely the next wave would've brought them out into that zone and warmed them up again, though it's entirely likely many died in this sudden freeze as well. Once they get revived, they would bury themselves again.

Mole crabs, normally about an inch and a half long, are indeed related to many kinds of crabs that are well known on the Oregon coast and Washington coast, but they're much smaller. They are in the same scientific order as hermit crabs, true crabs and shrimp.

Occasionally you can see the ocean appear to have a “bubbling” effect as huge numbers of mole crabs get tossed around by the tides and they struggle to dig themselves back in.

As common as they are, you don't see them that much. But in summer they come out in great droves and they feel kind of creepy as they brush across your bare feet if you're standing in the water.

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