Critter leftovers

I caught another low tide in daylight hours, without rain!, a couple of days ago. 

(I grumble at the poor scheduling of low tides all winter, as if there were someone in charge. But it's all in the numbers. We get one lowish tide every day, and one slight dip. And they come approximately 25 hours apart, so they always show up an hour later than the day before. Then remembering that we only get 8 hours of daylight in the winter, and you need 2 hours to get to the bottom of the intertidal zone and back before the water catches you, that leaves only one week every month available for exploring. And it's usually raining that week. Shouldn't grumble, then; the tide table people are doing the best they can. And anyhow, we're up to 11 hours in a day now. Summer's coming!)

Anyhow, I found some ex-critters at Oyster Bay.

Tunnels made by burrowing shipworms, Bankia setacea.

Not a worm, though; the "worm" is a clam. A long, worm-shaped clam with its shell carried in front of its mouth. It doesn't hide inside like "normal" clams; the shells are too tiny. Instead, it uses them to scrape away the wood, which it eats. As it goes along, it secretes shell material to line the walls of its tunnel; the white lines in the photo.

Anatomy of the shipworm. From Andrew Han, OHSU.

The shipworm log was on the dunes just above the tide line. Down on the beach, there were crabs. Or crab molts, anyhow.

Cheliped of a Dungeness crab. 

The well-worn shield of a kelp crab.

This was just at the top of the intertidal zone, where all the old seaweed mixes with dried vegetation from the land. In this spot, there were dozens of these kelp crab molts, all equally worn. Made me wonder; do they go in for group molts? Or is it a calendar thing?

Adult crab populations tend to molt simultaneously, females in the spring, males in the late summer.  (Oregon Coastal Crabbing Facebook post.)

So these were all females, it seems.

Long pincers of a female kelp crab.

And a solitary purple shore crab molt.

~~~~~~~~~~~~~

Otra vez pude visitar una playa anteayer.  La marea baja nos tocó durante el dia, y no llovía.¡Perfecto!

(Me quejo todo el invierno porque las mareas están mal programadas. Como si hubiera alguna persona encargada. Pero es cosa de números. Nos toca una marea baja por dia — la otra apenas baja un poquitito — y caen cada 25 horas, aproximadamente, cada una una hora más tarde que la del dia anterior. Y como los dias invernales son de apenas 8 horas, y se necesitan 2 horas si piensas ir hasta la orilla y regresar antes de que te agarre el agua, eso nos deja solamente una semana por mes para explorar en la playa. Y casi siempre está lloviendo esa semana. Pero es cosa de números, y no hay de que quejarme. Y además, ahora tenemos 11 horas de luz cada dia. ¡El verano está en camino!)

Bueno, encontré algunos animalitos en Oyster Bay. Sus huellas, por lo menos.

    1. Túneles en la madera hechos por un molusco bivalvo, Bankia setacea.

Aquí les damos el nombre de "gusano de barco". Pero no son gusanos, son almejas. Es una almeja extendida en forma de gusano que lleva su concha, muy pequeña, en frente de la boca. No se esconde adentro, como una  almeja "normal"; las conchas son minúsculas. Las usa, en cambio, para raspar la madera que le sirve de alimento. Mientras se adelanta, secreta sustancias para cubrir de concha las paredes de su túnel. Estas son las partes blancas en la foto.

    2. La anatomía de Bankia setacea. De Andrew Han, OHSU.

Este tronco estaba en las dunas en la zona alta intermareal. Más abajo, en la playa, había cangrejos. O por lo menos, las mudas de los cangrejos.

   

    3. Un quelípedo de un cangrejo Dungeness, Metacarcinus magister.

    

    4. El caparazón, muy desgastado, de un cangrejo quelpo, Pugettia producta.

Este estaba en la parte más alta de la zona intermareal, donde algas marinas viejas y secas se mezclan con hierbas de las dunas. En este sitio, había varias docenas de estas mudas de cangrejo quelpo, todas igualmente desgastadas. Me hizo preguntar; ¿es cosa que hacen estos cangrejos, mudarse en compañía? ¿O es algo que ver con la fecha?

Las poblaciones de cangrejos adultos acostumbran mudarse simultaneamente, las hembras en la primavera, y los machos al fin del verano.  (Oregon Coastal Crabbing Facebook post.)

Parece, entonces, que todas estas eran hembras.

5. Quelípodos largos de un cangrejo quelpo, hembra.

6. Y la muda de un cangrejito morado solitario, Hemigrapsus nudus.

More hole than wood

I often pick up chunks of teredo*-tunnelled wood on the beach. Sometimes I find an entire log riddled from end to end.

Each tunnel is coated with a layer of white calcareous material. The big hole is man-made.

Angular cut, showing the tunnel walls.

I measured the holes in a piece of tunnelled wood that sits on my desk (approx. 10 x 5 x 5 cm.). The holes are circular, and most measure 1 cm. across. Of 24 tunnels in this piece, 20 go straight through; two are slightly curved. On the log above, a few of the tunnels look curved.

When the wood dries completely, the white coating usually crumbles and falls off. It is only a couple of millimetres or less thick.

The tunnel of one teredo can be up to 2 feet long. In the log below there are thousands of tunnels.

The log. It looks like someone has cut a slab off, realized that the wood is unusable, and discarded the log. The outside looks normal.

*Teredos are usually called shipworms, but they are a species of clam, not a worm at all. The tiny bivalve shell is used as a file or scraper to burrow through the wood, which is their diet. Underwater termites!

Teredo navalis is a very destructive pest of submerged timber. In the Baltic Sea, pine trees can become riddled with tunnels within 16 weeks of being in the water and oaks within 32 weeks, with whole trees 30 centimetres (12 in) in diameter being completely warped within a year. (Wikipedia)

Group sculpture project

I've been sorting photos all afternoon and evening, cleaning and organizing the hard drive and storage, (working my way through 2010 today). And for a break, Laurie and I are sorting his paper photos, starting last week with the first ones from his disposable cameras, some 20 years ago.

What's that about "All things in moderation"? Never heard of such a concept!

I came across a photo that I loved, and thought I hadn't posted here. Looked it up in the archive, and I was wrong; it's here, in a post about shipworm. (Not a worm.)

Never mind; I still love the photo.

Carving by teredo clams, probably Bankia setacea, finishing by wind and waves.

Tomorrow, if the sun comes out again, I'm taking a break, attaching my new lens to the camera, and going out to load up on new photos. I've made space for them already.

When is a worm not a worm?

Answer #1: When it's a clam.

I grew up hearing about shipworms, the dreaded teredo worms that ate the logs that supported our wharves and float houses, and made our boats leaky. I'd seen their long holes in driftwood, and their white tubes cemented into the holes; long, snaking tubes for a tubeworm. Not until tonight did I learn that I had been completely mistaken about them all these years.

A teredo is a clam. An odd clam, to be sure; it's long (up to 2 feet) and snaky, like a worm, and the body's only protection is the calcareous tube it coats the tunnel with. But it does have the clam shell. On it's "head", or at least, the leading end. And it uses the double shell as teeth, to chew its way through the wood.

Its two shells, enclosing only the front end of the body, function as a tool, rather than a protective covering; their ridged and roughened surfaces are used for boring. (From bruceruiz.net)

Like other clams, it has two siphons. They are at the "tail" end. And the leading end is the foot. (It's a bivalve monopod.)

Drawing from bruceruiz.net

I was looking teredos up because Laurie took an interesting photo of shipworm-eaten wood today. I wanted to check my spelling, and ended up wandering around shipworm pages. Fascinating!

Like other clams, the teredo is a filter feeder, straining plankton from the water. But it also eats some of the wood it burrows in, with the aid of the bacteria it houses in special structures called "bacteriocytes". These bacteria produce enzymes that digest the cellulose of the wood. (Nobanis) They also "fix" nitrogen, and produce necessary amino acids.

(In this way, they are similar to termites, which also rely on protozoans and bacteria to digest the cellulose in wood. And similar, also, to us humans, whose intestines are home to many bacteria that work with us to digest our food. Not wood, though. Our bacteria can't handle cellulose.)

Laurie's photo. A rain- and wave-worn section of shipwormy log. Our local teredo is Bankia setacea.

Or there is Answer #2: When it's a crustacean.

The gribble, or gribble worm, as it is often called, also drills through wood found underwater,  like pilings, float logs, and boats. It is not a worm, but a crustacean, a marine isopod.

Limnoriidae are second only to theTeredinidae in the amount of destruction caused to marine timber structures such as jetties and piers. ... Gribbles bore the surface layers of wood, unlike the Teredinidae which attack more deeply. Their burrows are 1–2 mm diameter, may be several centimetres long, and have the burrow’s roof punctured with a series of smaller ventilation holes. Attacked wood can become spongy and friable. (From Wikipedia)

These critters seem to make their own enzymes to digest cellulose, but at least one species does find a use for symbionts:

L. tripunctata is unusually tolerant ofcreosote, a preservative often used to protect timber piles, due to symbiosis with creosote-degrading bacteria. 

Log showing gribble damage, and a teredo tube. Oyster Bay.

Come to think of it; I've never seen a live gribble or teredo; just their holes. I must remedy that.