2022-0211 A Day On The Beach
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Emerita analoga
Photograph from Monterey Bay Aquarium, with permission. This is a sand crab, a member of the family Hippidae. Unlike most crabs with which you are familiarr, Emerita live in the wave-washed zone of sandy beaches. They bury themselves in the sand, often right to the top of their shell, and the wave their frondy antennae in the wave washed zone to filter plankton out of the receding wave. Once the wave has receded past them, they bury completely into the sand.
As the tide comes in, they role up the beach, getting higher and higher as high tide approaches. Then as the tide recedes, they roll back down.
They are major prey of birds like Sanderling, Black-bellied Plover, Willets and Heerman's Gulls, which run or fly down toward the base of the wave as it recedes, probing for Emerita. As the next wave rises, they run or fly back up.
A lot of beach drama flows out of those dynamics. Birds running and flying and fighting over Emerita.
There is a sweet spot in the size of the Emerita. The larger they are, the more food the bird gets. But if they are too large to swallow quickly, the bird needs to get away from other birds that try to steal the prey.
