Fighting crabs

 A few years ago, on a hot summer afternoon, I was watching the tide roll in over a rocky breakwater. As the water rose between the rocks, crabs started to come out from their hiding places. More crabs and more, where a few minutes ago there had been no sign of life, just the hot, bare rocks.

The water rose until it reached a dried kelp stipe, cast up to bake on the rocks. And this surprised me: immediately the crabs attacked it; all the crabs, jostling and scrambling over each other to get at this dried kelp. More came out from hiding, dozens and dozens more, all of them grabbing at the stipe, fighting for a spot, pushing each other out of the way, tearing off bits and eating them. As the tide covered more of the length of kelp, so did the crabs until there was no kelp to be seen, just this dancing mass of crabs.

I should have thought of this sooner. My hermit crabs like kelp, too, and I would bring them fresh kelp from the shore. But cut kelp quickly turns slimy; I could feed them only a small piece and throw away any extra. And then, last fall I remembered the happy crabs.

So now I slice a long stipe into thin circles and dry it. And every couple of days I give the hermits and crabs a couple of dried slices. The first batch lasted them all winter; now they're starting on a stipe I dried a couple of weeks ago. 

Hairy hermit and his kelp treat.

One of the tiniest hairy hermits, with his scrap of kelp.

And a watchful crab, ready to fight for her meal, if necessary.

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Hace unos años, en un verano caluroso, estaba en un rompeolas mirando mientras subía la marea. Cuando el agua empezó a cubrir las rocas, aparecieron los cangrejos que hasta entonces habían estado bien escondidos, fuera del alcance de los rayos del sol. Más cangrejos, muchos cangrejos, donde hacía poco no se veían señales de vida, solamente esas piedras resecas.

El agua subió hasta que alcanzó un tramo del estipe de quelpo ya bien seco, tostado por el sol allí expuesto sobre las rocas. Y esto me sorprendió; en cuanto el agua tocó el quelpo, los cangrejos lo atacaron; todos los cangrejos, con gran entusiasmo empujándose, trepándose uno encima del vecino para llegar a este pedazo de quelpo seco. Salieron más de sus escondites, docenas más, todos tratando de agarrar el quelpo, peleando con los que se pusieron en su camino, defendiendo su sitio con ánimo mientras arrancaban pedazos para comer. Mientras la marea cubría más del quelpo, también lo hicieron los cangrejos, hasta que no se veía nada del alga, solamente esa masa pululante de cangrejos.

No sé porque no pensé en esto antes. A mis cangrejos ermitaños también les gusta el quelpo, y yo les traía pedazos desde la playa. Pero el quelpo cortado pronto se hace baboso, y solamente les podría dar un pedacito y tirar todo lo demás. Hasta que el otoño pasado, me acordé de esos cangrejos felices.

Y ahora me traigo todo un estipe largo, lo corto en rebanadas delgadas, y lo pongo a secar. Y cada dos o tres dias les doy una o dos rueditas de quelpo a mis criaturas. El primer estipe nos duró todo el invierno; ahora empiezan con el segundo. Y muy felices están.

Fotos: 

1. Un ermitaño "peludo" Pagurus hirsutiusculus, con su pedazo de quelpo.
2. Uno de los más pequeñtos, también comiendo quelpo.
3. Y un cangrejo hembra, algo preocupada por pensar que yo le puedo quitar su hallazgo. Lo defenderá con esas pinzas, si llega el caso.

A tasty orange

Last week's storms had tossed up many sponges with the torn seaweeds. Some were shredded, dead, sun-bleached, white, as I usually find them after a windstorm. But this week, most were still bright orange.

Orange finger sponge, Isodictya rigida, as found. On a bed of shredded rockweed, sea lettuce, turkish towel, and eelgrass.

I brought home a couple of pieces, one white, one still orange, and put them in the aquarium to see what my critters thought of them.

Orange (and white) finger sponge. With crab hiding underneath, hermit climbing in back.

The hermits climbed the white specimen, taking a few nibbles, then went back to eating the kelp stipe I'd brought them.

The larger crab (seen beneath the orange sponge) ripped big chunks off the orange sponge and ate them; an orange powder floated off into the water as he ate. That was in the first hour; after that, he and the other crabs went back to eating kelp. They've ignored both pieces of sponge ever since, and the orange piece is retaining its colour. I wonder if it's still alive; how can you tell, with sponges?

Central Coast Biodiversity says that dorid nudibranchs and blood stars eat this sponge. It looks like crabs are not so inclined. My little sea urchin has not made a move in its direction, either.

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Las olas y el viento habían aventado muchas esponjas, despegadas de su sitio en el fondo, hacia la playa, donde, arrastradas por el viento, terminaron en la parte superior de la playa, entre montones de hierbas y algas marinas hechas trozos. Algunas de las esponjas eran como las encuentro comunmente, rotas, blancas, blandas, muertas. Pero muchas eran nuevas, con su color fuerte anaranjado sin disminuir.

Me traje dos pedazos, uno anaranjado, el otro blanco, a casa para ver que hacían mis animales con ellos, y los coloqué en el acuario.

Allí, los ermitaños se treparon al pedazo blanco, tomando una u otra mordida, después regresando al kelp que también les había traído; allí se han quedado, comiendo kelp.

El cangrejo grande (que en la foto se ve escondido debajo de la esponja) arrancó grandes pedazos de la esponja grande, y se los comió; la esponja emitió un polvo amarillo mientras el cangrejo comía. Esto al principio, pero pronto perdió interés y se fue con los otros cangrejos a comer kelp. Desde entonces, los dos pedazos de esponja se mantienen sin cambio. (¿Estará viva la esponja amarilla? ¿Cómo se puede saber, con las esponjas, que son enteramente pasivas?

Central Coast Biodiversity dice que los nudibranquios y algunas estrellas de mar, (las estrellas sangrientas) comen estas esponjas. Parece que los cangrejos y ermitaños no cuentan entre sus predadores. Y mi pequeño erizo de mar no se ha acercado, tampoco.

Blobby bryozoans

Early winter storms tear and uproot the summer's crop of seaweeds. The mound along the high tide line, that in summer is mainly eelgrass with a sprinkling of sea lettuce and rockweed, in November becomes a full salad bar, multi-coloured, multi-textured.

In a short walk, I collected a bag of treats for my hermit crabs, with only one sample of each species, I ended up with a full grocery bag. Sea lettuce, of course. Two kinds of rockweed. Turkish washcloth, and a black, leathery, pimpled towel seaweed, four or five kinds of kelp, the invasive sargassum, several tiny blackish curly weeds, Pacific rose algae, red blades, rubbery threads, ... I didn't bother with eelgrass; the aquarium is planted with a fair crop from my last collecting trip.

I collected three pieces of a red algae that was coated with bryozoans. None of the algae were entire; they were stalked, and opened out into red blades, badly torn, rotting along the edges; I couldn't determine their shape or full size. But the bryozoans intrigued me.

At home, in a bowl. The stalks are encrusted with these hard blobs. The pink stub at the right seems to be a growing tip of the algae; there were several of these.

One of the blobs. Each little hole was the home of one zooid. If you look really closely (click for full size) you can see tiny pink pores on the body of each case.

Where the stalks met the blades, the structure changed; here they lie flat, one critter deep. Membranipora sp., maybe?

I don't think any were alive; they'd been lying out on the shore for a while. I looked while they were underwater, but saw no hint of movement.

I've been searching for an ID in my books and on the web, but can't find any that take these two forms on red algae. Blobs on rocks, yes. Single layers encrusting kelp, yes. Both together, no.

Membranipora membranacea is common on bull kelp on our shores; it makes circular, flat colonies on the blades. I could find no photos or record of it making these blobs.

And the crabs, hermit and "true" are happy, busy climbing and feasting.

You are what you eat

Northern winters are tough on the little beasties that live at the intersection of sea and shore. Temperatures change, often drastically, in the course of a few hours. Storms toss whole colonies up on the beach, bury them in mounds of slimy, rotten eelgrass, drop logs on top of them. Cozy shelters in the seaweed are stripped bare; on the scoured stones, there is nothing left to eat, nothing to hide a scuttling crab from the myriads of hungry birds following the tide line.

My tank critters are spoiled. The temperature stays put; so does the water. Food drops from on high every day. There are no birds, and the cat doesn't relish getting wet.

Grainy-hand hermit on the remains of a kelp holdfast.

But even here, winter brings its losses. I comb the beaches year-round, searching for salad fixin's and gym equipment for the hermit crabs. In summer, there are bright sheets of sea lettuce, tall stalks of eelgrass, some loaded with delicious hydroids and diatom fuzz, knobbly Turkish towels and washcloths, long, green hair, stubby rockweeds, and more. But in winter? Bare stones, washed-out shreds of unidentifiable weeds, stripped of anything edible. And tea-leaf black, dried eelgrass.

In earlier years, the tank in winter gradually lost all its greenery, until the hermits wandered about disconsolately on bare sand and stone. I supplemented their diet with human food, sheets of green algae meant for sushi wrappings. They liked that, but it fouled the water.

The last couple of winters have been different. A red sheet algae established itself in the tank, and now grows as enthusiastically as the land plague, Himalayan blackberry. I have to keep cutting it back with every weekly water change. But at least there's something fresh to eat, and somewhere to climb.

Red algae is even trying to grow on the hermit's shell.

The change in diet has influenced the colours of some of the tank's residents. Red are redder, greens are browner. The colour of the shrimp's innards changes day to day, depending on his last meal; red today, transparent tomorrow.

And even the normally transparent copepods are striped with red and yellow. Look closely at the hermit above; there are a dozen copepods visible on his shell.

Three females with eggs, one male; the rest, I can't tell.

Most copepods have one red eye, a streamlined body, and a forked tail. The females carry their eggs around behind them; usually one pouch (Order Calanoida), sometimes two (Cyclopoida), one to each side. In the dark one at the lower left, the pattern is easy to see; red eye above, green bag beneath. The small, pale copepod at upper left may be a male of the Cyclopoida; his long, forked tail is just visible.

Drawing adapted from one by Jesse Cladgett.