When I was wading with my family at the edge of the Pacific Ocean, I looked down at the swirling waters and the pebbles tossed and bashed against a few large stones. I wondered what animal could live here when it couldn't even be sure where the water would stop and the dry beach would begin after each wave. As we looked closely, we saw small brownish gray football shapes swirling around.
These footballs were sand crabs dislodged by the waves. When we caught one in our shovel, it immediately dug backwards into the sand. We realized that burying must have been some key to its survival.
After these field observations, I researched the crab on the Monterey Bay Aquarium website. The floating football type of behavior occurs when they are knocked out of their preferred hunting ground, being buried in the sand in the swash zone, where the surf hits. They are one of the few crabs that are able to swim or tread in the open water.
They immediately swim back down to bury themselves in the sand. After the tide has reached its highest point and is receding back down into the ocean, they reach up into the sunlit-rayed water and grab small bits of food. They can do this several times in the time span of just one receding wave.
Like all crabs, they have ten legs, but they lack pincers (and I thought my avoidance of getting pinched was due to my crab-handling skill). They move backwards, a key fact to bear in mind when trying to identify the head, which will be at the back of the moving animal.
One of the most unusual facts about their shape is that the male is only about one-half the size of the female (which reminds me of raptors). At one point, we caught two crabs in our shovel (of course to let them go quickly). My daughter theorized that the mommy was taking such good care of the baby. However, I became skeptical due to my dim recollection of crab larvae spending time as anonymous plankton and the tendency for crustaceans to have many thousands of eggs-- thus making quality mothering time somewhat impossible. Upon further research, I have now concluded that we found a male and a female.
We found sand crabs by simply staring down at the water at surf's edge. We also saw quick-swimming sand-like creatures that perhaps serve as the crabs' food. I read that, in turn, surf perches like to eat sand crabs as do gulls.
I have also read that if you want to find sand crabs, simply dig a hole in the wet sand and swirl water around.
Always be careful not to crush the creatures and to let them go quickly. Also watch your step after you let them go. We also discovered a hermit crab perhaps lost and displaced from its tide pool (since I believe that they do not like to wander about far from rocks). We tried to teach our daughter as much as possible to watch where she stepped even in this ocean desert type of environment, where not much seems to live.
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