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Walk on the Winter Beach

Diamond-back tritonia, Tritonia festiva. Photographed January 2013 at the  north end dock by Rayna Holtz.
Diamond-back tritonia, Tritonia festiva. Photographed January 2013 at the north end dock by Rayna Holtz.

You can go to another world without leaving Vashon. By spending a winter evening on the shoreline with a flashlight you will soon find a little-known yet vast community of living intertidal beings under and near the north end ferry dock.  The moon will be almost full, so if the clouds part we will have dim silver light from stars and moon to limn the other-worldly habitats consisting of pilings, watery eelgrass beds, boulders, and sand.

When the ebbing tide reaches its low of -1.4 feet around 8:45pm, we may be able to see some of the fancy orange sea pens that live where they can enjoy the extra current from ferry propellers near the deep end of the dock. One of their predators is the lovely diamond-back tritonia, Tritonia festiva, about two or three inches long. With its white stripe connecting ribbon-like curlicue gills, it looks like a translucent gift-wrapped surprise, a Christmas treat for beachwalkers.  These nudibranchs eat soft corals, and the orange sea pens, Ptilosarcus gurneyi, are a species of octocoral. When a sea pen is approached by a diamond-backed tritonia, it does not think of Christmas gifts or Santa though! If it thinks of anything other than escape, it thinks of monsters!  A sea pen can deflate and bury itself in sand, or it can uproot itself and float away—effectively eluding some hungry sea stars--but sometimes too slowly to avoid losing some of its polyps to a hungry nudibranch that is already upon it.

There are many engaging creatures and seaweeds of many colors and textures on our shorelines, and most play out varying dramas involving life and death, hunger and escape, hunting and reproduction. We may see nudibranch eggs of several species clinging to pilings or rocks.  We will also see barnacles, chitons, limpets, and rockweed clinging to these hard surfaces. In the sand and shell around the pilings we may see bright-eyed shrimp and tiny decorator crabs with spindly legs and tufts of algae growing on them for disguise. From the large red rock and kelp crabs under the dock and in the eelgrass, down to small porcelain and black-clawed crabs hiding under big rocks, there are a dozen crab species living in the vicinity. Sometimes there is a tiny octopus or a squid.  Many species of shellfish have left their shells in the sand for us to admire, and we often see small periwinkles or a big moonsnail. We will hope to find some healthy sea stars, survivors of the Sea Star Wasting Disease that killed off most of their kin over the past three years.

The Vashon Beach Naturalists will be wearing bright yellow-green vests with reflective strips, eager to answer questions and look at what you find. If someone in your family gets chilly, there will be hot chocolate and tea at the illuminated booth on the north side of the dock, along with a few chairs and a pile of beach guides.  Dress warmly, wear knee-high rubber boots, and bring a flashlight with extra batteries. And be sure to park in the lot on the hill, so that you don’t use spaces meant for customers at La Playa. We welcome whole families!  For further information call Rayna at 463-3153.

Oh, Vashon gals won’t you come out tonight, come out tonight, come out tonight?
Oh, Vashon guys won’t you come out tonight, and glance by the light of the moon?