Tubes of sand, tubes of glass.

Empty sand. A clean, firm, flat beach; easy walking, a good place for a run with a kite or a bouncy ball. A good place to build a sand castle or sculpt a sea monster. 

But watch where you step. The sand is never as empty as it looks. Under your careless feet, hundreds, thousands of busy critters have set up housekeeping. Sometimes they build chimneys.

Bamboo worm tubes, Axiothella rubrocinta.

A pink worm with red bands lives in each of these tubes, made of a thin paper-like material, coated with glued-on sand. The worm may grow to 20 cm. long; the tube that stands on the surface is about 5 cm. tall.  It rests in the tube head downward and expels waste matter through the open top. According to the Marine Life Encyclopedia, each tube may be "used to brood juveniles."

I found one out of the tube near here 15 years ago:

Gone a-wandering.

And then I went down another rabbit hole. I wondered what these worms ate. Some intertidal worms are active hunters, carnivores eating other worms and beach animals. Some spread out tentacles to catch plankton, some use sticky mucus to trap prey. Some are scavengers, eating algae and the remains of other organisms. And these?

 A University of the Pacific study of the feeding habits of the bamboo worms, provided an answer, and more; imagine building glass tubes for these critters to watch them eat! And they eat the sand, digesting "diatoms, fecal pellets, algal fragments, and mesopsammmic organisms" (these last are animals that live between the sand grains). The indigestible sand grains are ejected or "eventually ... incorporated into the tube." Their activity, moving sediment, pumping water, keeps the sand oxygenated and healthy. One worm processes an average of 6.5 gm. of sediment per day, up to 11.5 gm/day near the end of summer. 

"It has been calcu1ated that Axiothella can completely recycle the upper five cm. of sediment in nine to ten months."

Did you know you were walking on food?

By the way, no (well, as few as possible) worms were harmed during this study: 

"Before and after the experiment,  each specimen was cleaned, blotted and weighed as described previously. The worm's ability to burrow both before and af'ter experimentation was used as an index to a specimen's healthiness."

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 Arena limpia, pura arena. Una playa vacía, compacta, extendida; donde es fácil caminar, donde puedes correr con un papalote o botar una pelota. Un buen sitio para construir un castillo de arena o esculpir un monstruo marino.

Pero ten cuidado donde pisas. La arena nunca es tan solitaria como parece. Bajo tus pies descuidados, cientos, miles de criaturas han hecho sus hogares. A veces hasta construyen chimeneas.

1. Los tubos de los gusanos de bambú, Axiothella rubrocinta.
Un gusano color de rosa con bandas de rojo fuerte vive en cada uno de estos tubitos, hechos de una materia como papel de pergamino, cubierto con arena. El gusano puede alcanzar hast 20 cm. de largo; la porción del tubo que se extiende sobre la arena mide unos 5 cm. El gusano se acomoda en el tubo con la cabeza hacia el fondo, y elimina sus deshechos desde la apertura superior. Según la Encyclopedia de la Vida Marina, cada tubo puede "usarse como criadero de gusanos jóvenes."
2. Hace 15 años, descubrí uno de estos fuera de su tubo.

Y me preguntaba; ¿Qué comerán estos gusanitos? Porque unos gusanos intramareales son carnívoros y cazan su presa activamente. Otros extienden sus tentáculos para atrapar el plancton; algunos se cubren de moco pegajoso para el mismo fin. Algunos son buscadores de deshechos, y comen algas y los restos de otros organismos. ¿Y los gusanos de bambú?

Un papel de la Universidad del Pacífico, estudiando los costumbres de los Axiothella sp. me dió una respuesta. Y más; ¡imagínate que construyeron tubitos de vidrio para poder observar como comían estos animalitos!  Y comen la arena, digiriendo "diatomeas, partículas fecales, fragmentos de algas, y organismos que viven en los intersticios entre los granos de arena." La arena, que no se puede digerir, se elimina o "con tiempo ... se incorpora en el tubo." Esta actividad, agitando el sedimento, bombeando el agua, mantiene la arena sana, y oxigenada. Un solo gusano procesa un promedio de 6,5 gramos  de sedimento a diario, y hasta 11,5 gramos cerca del final del verano. 

"Se ha calculado que Axiothella puede reciclar completamente los 5 centímetros superiores en un espacio de nueve a diez meses."

¿Sabías que pisabas comida?

Hay que aclarar que ningún (o tan pocos que era posible) gusano fue dañado durante estos experimentos: 

"Antes y después del experimento, cada animal fue limpiado, desaguado, y pesado como describimos anteriormente. La capacidad de carvar que demostraba el gusano tanto antes como después del experimento se usó como índice de la salud del organismo."

Designs in blue and grey

 I liked the pattern that sea foam made on waves coming ashore over smooth, flat sand.

Attenuated waves

Further down the beach, with rocks making a breakwater, the only waves are sand waves.

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Me gustaron los diseños que hizo la espuma de mar en las olas que se quiebran en una playa arenosa lisa y plana.

Fotos: Las olas, que se disminuyen mientras avanzan. Y, más adelante en la misma playa, las rocas forman un rompeolas y las únicas olas son las de la arena.

Arrows pointing backwards and wavy letters

In January, when the water is too cold for wading, and the wet stones and sand are cold enough to cause a bone-deep ache in rock-flipping and sand-digging fingers, we behave more sedately than usual, walking upright on the sand, hands in gloves and pockets, eyes peeled for what we can see without stopping and getting chilled.

Sand, water and sky. Patterns in blue and grey. Laurie usually looks up to the sky and the distant snowy peaks. I'm more likely to watch what's in front of my feet.

Duck footprints. Probably mallards. Three toes, and distinct webbing.  Ducks toe in, which makes them waddle.

A duck has four toes; three facing forward, webbed, and a fourth, called a hallux. It faces backwards, is small and higher up on the leg. Sometimes it leaves a mark on the footprint. More often, it doesn't.

Gull tracks. The tip of the hallux left a mark in this wet sand. The footprint is about twice the size of the duck prints above, and the webbing isn't as marked. Like ducks, they toe in.

Heron tracks in soft sand. I don't know what makes those dotted-line furrows.

Heron track with my big boot for measurement. About 6.5 inches. (The heron's foot, not mine.) These are big birds.

Heron track on hard-packed sand. He drags that rear toenail. There is no webbing; the heron is not a swimmer.

Something different; check this out!

Just sand, sculpted by the tide.

But: this was flat, flat beach. Very flat; I want to emphasize this. But look at the photo from a bit of a distance; to me, it looks hilly. From a few steps back, the hills grow into small mountain ranges. And sometimes, when it catches my eye suddenly, I see what looks like letters among the lines. I can't read them; they morph into different shapes with the slightest head movement. (If I'm looking for them, I don't see them.)

What do you see?