Species Feature: Coquina Clam

I have an odd ritual when I go to the beach. Once I drop my things, I make a beeline to the surf’s edge and stalk up and down the shoreline, hands on my hips, frowning down at the sand. Eventually, I’ll stop, bend forward, and snatch down with both hands, then examine my captured clump of shoreline.

If you guess that I’m shell hunting, you’re partially in the right. It’s not empty, abandoned shells that I look for, though. It’s live coquina clams.

When I was in elementary school, my uncle first clued me into the fact that there are more reasons to dig at the beach than just sandcastle construction. My family came down to visit him and my grandparents on the Florida Gulf Coast and–of course–went to the beach. I was hoarding fistfuls of washed-up shells and showing them off to the adults of the bunch. My uncle indulged my excitement and poked through my finds, noticing that I’d chosen several dainty shells composed of two pieces and still joined in the middle. When the two sides were splayed out fully, I thought they looked like tiny angel wings.

“Want to see something cool?” he said. I was certainly not going to pass on that opportunity. He waited for a wave to recede, then dug his hand into the sand and flipped over a scoop of it. My jaw dropped. A new wave passed over the upended pile and a half-dozen shining, gem-like creatures scooted back down into the sand: variable coquinas.

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Variable coquinas, Donax variabilis, are small burrowing clams. They get the name ‘variable’ because they come with a huge range of appearances. They come in all sorts of colors, especially purples, oranges, grays, yellows, and whites, as well as many patterns. Some have concentric arcs on their shells, while others are decorated with stripes that look like sun rays. You might even find clams that have both, creating a checkerboard effect.

These beauties live in the intertidal zone, meaning they’ve specialized to thrive in the area between the high and low tide lines. They migrate up and down the beach as the tides change so that they can stay in the sweet spot of the water’s edge. There, they don’t have to worry about drying out, but they’re also in such shallow water that aquatic predators, like small fish, can’t reach them. As long as a little bit of water is washing over them, they also have access to food; one end of their body has two tubes called siphons, which they stick above the surface of the sand. They pump seawater in through one siphon and then filter out algae and plankton for a tasty meal before pumping the water back out the other siphon.

Coquinas burrow in the sand with a muscle that they extend out of their shell, fittingly called the foot. If you dig one up, you can sometimes see the foot extend and prod around in their surroundings. I always thought it looked like a long, clear tongue that they were sticking out at me.

Even though they’re no longer a surprise to me, I love digging up coquinas to this day. It always amazes me that the beach, looking so empty of creatures, is such a vibrant habitat under the surface.

And the sight of a clam wiggling its way back down into the sand is just plain cute.

Swimmingly yours,

Sea

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