The rock eaters

See a sea urchin on the shore; a round ball covered with spikes. No apparent feet, eyes, grabbers; separated from the ground by all those spikes; how does such a critter manage to live? But they do, and they change the world around themselves.

Red sea urchin on beauty bush at low tide.

The spines are moveable. And beneath them, but extending out beyond them when wanted, are many tube feet with suction tips; with these, the urchin can walk, climb, collect food and convey it to its mouth on the underside. Or even hold rocks or shells or algae over itself; camouflage, perhaps, or protection.

Many of the sea urchins I saw on this low tide exploration were carrying clumps of hydrocorals, or sheets of sea lettuce. Some carried empty limpet shells or stones.

Red sea urchin in sandstone pit, wearing sea lettuce.

Then there's the mouth. On the underside, just a circular hole with five calcareous plates, called Aristotle's lantern. With these plates the urchin tears up its food. But it also tears into rock, digging holes for itself with them. Sandstone is a soft rock; this flat sandstone beach has many such pits.

They can even trap themselves in these holes:

Strongylocentrotus droebachiensis ... uses its strong Aristotle's lantern to burrow into rock, and then can widen its home with the spines. Usually, this sea urchin can leave its hole to find food and then return, but sometimes it creates a hole that gets bigger as it gets deeper, so that the opening is too small for S. droebachiensis to get out. (Wikipedia)

The plates wear down, of course, what with gnawing away at stone, but they grow back, being completely replaced by a couple of months growth. (Wish my teeth would do that!)

Red sea urchins typically live in small groups, of about 5 to 10 individuals. The greens, though are extremely gregarious:

Crowd of green sea urchins in a tidepool.

They eat algae, mostly brown algae; they love kelp, and are less fond of the green sea lettuce. And they can be responsible for devastating entire forests of the huge bull kelp, the largest of all the seaweeds. It seems strange; the forests are so dense, the kelp so tall and strong; how can a tiny, fragile critter have such an impact?

This is how; look at this photo:

Strength in numbers. Also present, a purple and a red urchin, and a leather star.

At the bottom of the low intertidal zone, all the areas still underwater were carpeted with these green urchins. They eat away at the holdfast of the kelp, releasing the tall stipes and fronds to be tossed up to dry on the shore, and leaving behind what are called "urchin barrens".

But we still have kelp because there's a food triangle: sea otters live in the kelp forests, eating the sea urchins that eat the kelp.

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

Mira un erizo de mar en la playa; una pelota cubierta de espinas. No se le ven pies, no tiene ojos, no se le ve nada con que agarrar su comida, mantenido aparte del suelo por todas esas espinas: ¿cómo es que llegan a sobrevivir en esas condiciones? Pero sí viven, y hasta cambian el mundo alrededor suyo.

Primera foto: un erizo de mar rojo sobre alga marina.

Las espinas se mueven. Y debajo de las espinas, pero capaces de extenderse más que las espinas, hay una multitud de pies tubulares, que terminan con ventosas; con ellos, el erizo puede caminar, trepar, capturar comida y llevarla a la boca que tiene en la parte inferior del animal. Y hasta puede agarrar cosas como conchas o algas o incluso piedras para sostenerlas por encima, tal vez como camuflaje, o protección.

Muchos de los erizos que encontré en este dia se cubrían con trozos de lechuga de mar o manojos de hidrocorales. Algunos cargaban conchas vacías de lapas o pequeñas piedras.

Segunda foto: un erizo rojo en una poza en la piedra, llevando lechuga de mar como sombrero.

Y considera la boca: es simplemente un agujero en la parte inferior, cubierto con cinco placas calcáreas, a las que llamamos en conjunto la linterna de Aristóteles. Con estas placas, el erizo mastica las algas que son su comida. Pero también las usa para romper piedra, haciendo hoyos en donde se puede refugiar. La arenisca es una piedra muy suave; en esta playa de arenisca se encuentran múltiples pocitos.

Les puede resultar un poco peligroso, cuando se llegan a atrapar en sus propios pozos:

Strongylocentrotus droebachiensis ... usa la linterna de Aristóteles para excavar la piedra, y luego puede ampliar la poza con sus espinas. Normalmente, el erizo puede abandonar la poza para ir a buscar comida y luego regresar, pero a veces hace un hoyo que se agranda mientras gana profundidad, con el resultado de que la apertura es demasiado chico para que el erizo pueda salir. (Wikipedia)

Las placas se desgastan, puesto que están royendo piedra, pero siguen creciendo hasta reanudarse completamente en un par de meses. (¡Ojalá mis dientes hicieran lo mismo!)

Los erizos rojos viven en pequeños grupos de 5 a 10 individuos. Los verdes, en cambio, son extremadamente gregarios.

Tercera foto: grupo de erizos verdes en una poza intramareal. 

Comen algas, principalmente algas cafés. Les gusta el quelpo, y no tanto la lechuga de mar. Y son capaces de destruir un bosque entero del quelpo grande, Nereocystis luetkeana. Parece extraño ¿cómo puede ser que un animalito tan pequeño, tan frágil, tener un impacto tan fuerte sobre estas algas gigantes?

Así: mira cuarta foto: un ejército de erizos verdes.

En la parte más baja de la zona intramareal, todo el agua llevaba un tapete de estos erizos. Comen los rizoides fijadores del quelpo, dejando que las olas lleven el resto a echarlo en la playa a secarse, dejando lo que llamamos desiertos de erizos.

Pero todavía tenemos quelpos. Porque hay un triángulo ecológico; las nutrias marinas que viven en los bosques de quelpos comen los erizos que comen las algas.

Pointy

 Reaching out ...

Spiky. Baby sea urchin sheltering in empty mussel shell.

Tentacly. Plumose anemone, "Metty", feeling fine.

The sun came out this morning, and I went for a long, long walk. Tomorrow there'll be photos of beach findings.

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

Estirándose ...

Mi erizito de mar, descansando en una concha vacía de un mejillón.

Y mi anémona plumosa, a la que he dado el nombre de "Metty", feliz, esperando su desayuno.

Hoy salió el sol en la mañana, y me fui a caminar por largo rato. Mañana, habrá fotos de lo que hallé en la playa.

Spines and cog wheels and five teeth

On my last trip to the beach, I had on my "shopping" list: some eelgrass with roots, because the hermits love to climb it and to eat whatever grows on it, hydroids and bryozoans and the like; some fresh sea lettuce, if I could find it, because the crabs had eaten all of the last batch; a bit of kelp, to keep my plumose anemone healthy, and a length of kelp stipe, because both the crabs and the hermits eat it, all the more enthusiastically as it disintegrates; a small stone with barnacles for the snails to eat; some snails for the anemones to eat. The little underwater community demands variety!

In the latest offerings torn up by the tide from the sea floor, I found the kelp and a good handful of eelgrass, and at the last minute, a nice blade of fresh sea lettuce. It all went in my bag. There were no barnacles this time; the carnivorous snails will have to make do with mussels for now.

Washing off the sea lettuce at home, I discovered that it was hiding a tiny sea urchin; lucky for it that I collected that piece; otherwise, tossed up by the tide and abandoned, the urchin would have died.

It's cruising around the upper levels of the wall of the aquarium, eating algae. And showing off its five-pointed star mouth, chomping away.

Mouth side of the urchin. About 1 cm. across the whole animal. (It's a baby.)

The arrangement of five teeth is called "Aristotle's lantern", not because they look like a light, but because Aristotle first described them. They open and shut, scraping at the algae; sometimes they can be used to scrape a hole for the urchin, even in rock.

The test, or hard shell of the urchin has spines; they're jointed, so they can rotate. Here you can see the purple joints on the spines. The urchin "walks" on its spines, its tube feet, and even its teeth. The tube feet protrude through holes in the test, and are soft and flexible. Each one ends in a round sucker; these are being used to hold onto the glass, and to move about. Quite rapidly, it turns out.

Zooming in. The suckers on the tube feet are like little cog wheels.

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

En la última vuelta a la playa, my lista de "compras" consistía en: hierba marina "Zostera", con raices y todo, porque a los ermitaños les gusta trepar en lo alto y además comen lo que crece en la hierba, sea briozoos o hidroides u otras algas; un poco de alga "kelp" para mantener sana a mi anémona plumosa, y una sección del tallo porque los cangrejos y los ermitaños lo comen con gusto, tanto mayor cuando ya está desbaratándose; un poco de lechuga marina, porque los cangrejos ya comieron lo que les traje hace una semana; y una piedrita con bálanos para los caracoles carnívoros. ¡Mi pequeña comunidad acuática pide una dieta variada!

Entre lo que aventaron las olas, encontré la hierba, el kelp, y por fin, un trozo de lechuga marina. No había piedras con bálanos esta vez; los caracoles se las van a tener que arreglar con los mejillones.

Limpiando la lechuga marina en casa, descubrí que protegía un pequeño erizo de mar. Tuvo suerte; aventado a la arena por las olas, se hubiera muerto. Ahora da vueltas en la parte superior del acuario, comiendo algas.

Saqué fotos de su boca, ya que come con la boca al vidrio.

Tiene cinco "dientes"; se le llama a este conjunto la linterna de Aristóteles, porque fue descrito por el filósofo antiguo. Estos raspan a la superficie, cortando algas. Pero son suficientemente fuertes para también excavar hoyos para protección del animal, incluso en roca.

El animal se mueve usando sus espinas articuladas, vistas aquí, color crema con segmentos color morado. También para caminar (¡y bastante rápido que se mueve!) usa los pies ambulacrales y hasta esos cinco dientes.

Los pies ambulacrales son tubitos que se extienden desde poros en el caparazón. Son muy flexibles, y terminan con un botón que se adhiere a las superficies. En la segunda foto se puede ver como terminan con una ruedita con dientes.

Better late ...

Shut up in my house, without all the busyness that took up my time before the virus struck, I've turned to catching up on all those "when I get a round tuit" tasks. One has been sorting and culling over a decade's worth of photos on my hard drive.

I found these photos, taken in the Campbell River aquarium three summers ago, and never converted from the RAW files.

Lion's mane jellyfish

All the species in this aquarium are found locally and captured in the spring of the year. The lion's mane is commonly seen washed up on our beaches. Those long tentacles carry a sting; never pick up a lion's mane with bare hands!

Coonstripe shrimp, commonly found beneath the docks next to the aquarium.

Orange sea pen. This is a sub-tidal species.

This is not a single animal, but rather a colony of polyps arranged along a common stalk, the first polyp. (See Biodiversity of the Central Coast.)

Red sea urchin, on kelp.

At the end of the summer, all these critters were taken back to their respective homes and released.

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

Ahora que estoy encerrada en casa, sin todos los compromisos que me mantenían ocupada en los dias "antes del virus", he vuelto a todos esos quehaceres que había dejado para mas tarde. Uno de estos es revisar y seleccionar las fotos guardadas desde hace hasta diez años en la computadora.

Encontré estas, tomadas en el acuario local hace tres años, y abandonadas desde ese dia.

La primera es una medusa melena de león, muy común en nuestras aguas. Esos tentáculos llevan nematocistos venenosos. Nunca hay que tocar una des estas animales con las manos sin protección.

La segunda es un camarón rayado; estos viven debajo del muelle al lado del acuario.

La tercera foto es una pluma marítima; se encuentran debajo del nivel de la marea. No es un solo animal, sino una colonia de pólipos.

Y la cuarta es un erizo de mar rojo.

Todos estos animales fueron capturados en los alrededores de esta ciudad en la primavera. Cuando se cierra el acuario para el invierno, se les regresa a su lugar de orígen.

Prickly

This was a small urchin that came home on seaweed for the hermits.

Green sea urchin, Strongylocentrus droebachiensis

The test is pink, fading to grey when the urchin dies. Spines green; they're in constant motion, pulled back and forth by skin and muscle tissue over the test. Tube feet (brown/black) protrude through holes in the test; they're moved by water from the internal vascular system.

The five plates in the centre are like teeth; they scrape food off the surface of seaweed and rocks. The whole centre structure is called "Aristotle's lantern".

This structure was named for Aristotle, a Greek philosopher, scientist and teacher who described the structure in his book Historia Animalium, or The History of Animals. In this book, he referred to the "mouth-apparatus" of the urchin as looking like a "horn lantern." Horn lanterns at the time were five-sided lanterns made up of panes of thin pieces of horn. The horn was thin enough for light to shine out, but strong enough to protect a candle from the wind. (thought.co)

Tube feet, with their suction tips, looking for something to grab on to.

A pair of babes

I explored a new area on the beach at low tide, and found many tiny starfish, mostly mottled stars, all looking healthy.

Here's one:

Star, Evasterias troschelli, with my fingertip and a baby sea urchin. I don't know what the brown circle is.

I have small fingers; that fingernail is 1/2 inch across at the widest point, which makes the baby star just under an inch, arm tip to arm tip, and the urchin about 1/8 of an inch, not counting the spines.

No star is an island

A few more starfish. But nothing on the shore lives alone; the more time you spend looking, the more complex you realize the community is. Even in a simple photo of a stone and a star, there's something I didn't see until I got it home.

I think these two are juvenile mottled stars. Look for the fly on the upper snail shell, an opportunist dropping in for a snack as soon as I turned over the stone. Also if you look closely, you may find four baby (infant) sea urchins, tiny snails, and a flatworm.

Four-and-a-quarter arm star. Ochre sea star, with purple tips to his arms. On a bed of assorted seaweeds, over sandstone. Between the weed and the stone, a scramble of hermit crabs.

A small purple star with an unusual stripe down his arms. Around him on the stone, a few worms in their own casing of sand, exposed when I flipped the stone. The spirals are calcareous tubeworms, and the slimy stuff may be flatworm eggs, but I wonder about the patch at the bottom, with its smokestack.

Two more juvenile mottled stars. purple and pink, and blue and green. Also present; a hermit, all scrunched up, the remains of a bryozoan colony, barnacles, tubeworms, bits of a pink encrustation, and seaweed.

Coming up: worms, worms, worms.

Just exploring

I drove up to Kelsey Bay, 75 km north of Campbell River, following a winding road off the highway, through Sayward village (pop. 400) and on until I came to a dead end at a small, rocky, dark beach, slippery with rockweed and shreds of kelp, splashed with wind-driven waves. There, I went looking for critters, tripped and ended up in the water, froze my fingers until I couldn't feel the camera buttons, and then found the only local coffee shop closed. An interesting afternoon; a good day!

Broken, empty green sea urchin, still retaining most of its spines.

Fragment of the shell, from the inside.

There will be more photos tomorrow; scenery, kelp, and critters.

More practice shots: white on white

I'm still learning how to use the new gear, working with different settings and configurations of camera, lens, and reflectors. I decided it would be simpler to practice on something that was not constantly getting in fights, or wandering off for a bite to eat, or just turning his back on me. Not a hermit nor a shrimp, in other words.

I chose, instead, an old sea urchin test, without its spines, and a sprig of dried everlasting flowers.

This first photo is as it came out of the camera; no processing at all, other than resizing for the blog.

Almost lace. And there are a few remnants of spines, after all.

For this next one, I changed the aperture and moved in closer. That produced some noise, which I partly removed in processing. Still, there was minimal work to be done; despeckling, cropping, resizing.

Close-up of urchin buttons and holes. I think they're where the spines were inserted.

And the everlasting; again, with minimal processing; removing a dust speck, resizing, sharpening.

White on white, with hints of pink.

I'm pleased. Depth of field is still something to work with; for example, on the urchin, every part that curves away from the camera is out of focus. And the lens definitely loves light. For these, I had the flash, a spotlight, general room lighting, a white sheet, whiter paper, and two big white reflectors (one is the lid of a big plastic bowl; what works, works.)

More practice shots tomorrow; something alive, again.

Wriggly hitchhiking pincushion

I brought home a few stalks of Turkish towel for my hermits, and this little critter came along for the ride.

Sea urchin, about 1 cm. across

In the aquarium, he burrowed into the sand quickly, but later he was out in the open riding this snail, and carrying pieces of shell and sand grains, possibly as camouflage. It would have worked better if he had ever stopped waving those spines about.

Tonight, cleaning the tank, I found him back on the Turkish towel. He dropped off onto my fingertip, and attempted to glue himself there. Adventurous little beastie!