A Brief Encounter with a Western Sea Roach

Western Sea Roach—Ligia occidentalis

The sea, once it casts its spell, holds one in its net of wonder forever.  Jacques Cousteau (1910-1997)

Years ago, along the northern Oregon Coast, I found a small metal box without a lid half-buried in wet sand. The box measured roughly six by six inches square, and just as deep. When I tried lifting it, it wouldn’t budge. The box, half filled with seawater, held a dazzling treasure—a colorful creature as long as my pinky.  Along its back were translucent tubes (like a sea anemone) tipped with neon orange and yellow, outlined with white. It was a sea slug, probably Opalescent Nudibranch, Hermissenda crassicornis; nudibranch (pronounced: noo-duh-brank) hunts tide pools feeding on sea anemones, and sometimes other nudibranchs. Though considered a common creature of tide pools, from Alaska to California, I have not seen one since.

More recent, while wave-watching along a jetty on the southern Oregon Coast at low tide, I met an isopod I’d never seen before. How I saw the small creature camouflaged among rock and sand was sheer luck! So glad I didn’t step on it. I drew my camera and took a few shots seconds before the creature slipped between the cracks.

Several weeks later, at home in my studio sifting through beach photos, I came across the isopod I’d seen on the jetty. It turned out to be the western sea roach, Ligia occidentalis, a.k.a rock louse—a scavenger that forages rocky beaches, especially for algae. I’d never seen one before, and was lucky to have encountered this one since they tend to hide during the day among rocks and crevices just above the high tide zone. When I had found this one, it was late afternoon during an outgoing tide and was likely heading for the hunting grounds of the intertidal zone.

The western sea roach is a land dweller, and though it doesn’t live in the sea, it needs the sea to survive. It must keep its gills moist always. Staying hydrated, the western sea roach dips its abdomen in seawater; a necessity that forever ties the creature with the sea. It can then forage away from water, so long as it doesn’t stray too far. The western sea roach must also be careful not to get trapped and submerged by waves; otherwise, it will drown. A really cool factor is that the western sea roach controls how it is seen. Just like squid, it has light-reflecting cells called “chromatophore” that enables the isopod to change colors to match its background. Mine displayed a mottled camouflage that blended beautifully with sand and rock.

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