Aquarium update

Surprising happenings in my aquarium! Up until a few months ago, almost every time I changed the water in the tank, I removed everything so that I could scrub the walls without scratching them or upsetting the residents. The hermit crabs and crabs went in one dishpan, the snails in a yogurt container, the barnacles and shells with anemones attached in another, seaweeds and eelgrass in a bucket, and so on. While they were there, I fed the hermits, checked over everything for problems, weeded out dying seaweed.

And, putting everything back, I counted. At last count, there were 40 hermits, most of them tiny. And 4 crabs. A varying number of snails; up to 70, down to about 40 (the big anemones eat them and I go to the beach for more.)

Orange-striped green anemones in old barnacle shells.

After the debacle with poisoned water this winter, I'd not been able to find a reliable source of water, so instead of bringing in new every couple of weeks, I've been cleaning and changing the filters a couple of times a week, adding fresh, filtered water as needed to bring down the salinity. I've scrubbed the walls and weeded, but without emptying the tank; it all takes time. So I haven't been counting my resident population.

Pink-tipped green anemone with her baby (clone) in an old moon snail shell.

The water situation improved. I found a source of safe water, and cleaned out the tank. And counted the hermits and shore crabs. I expected to have lost a few over the winter; nothing lives forever. But when I counted (three times, to be sure) there were 43 hermits, and still the 4 crabs, full-grown now. The tiny hermits were bigger now; I didn't see any pinhead-sized ones. But they were all there. Amazing!

A couple of the crabs were carrying young. They took good care of their brood, but of course, it was all a waste, wasn't it?

Out in the wide ocean, the baby crabs (zoea and then megalops) are microscopic free-swimmers that become part of the plankton, the base of the food chain that feeds invertebrates, fish, birds, and ultimately us. Life is precarious out there; everything is looking for a tasty bit of wriggly meat. Ma crab has released thousands of zoea; only a very few will survive.

In my tank, predators are few. The oysters, the anemones, the worms; that's about it. Except for one big, starving, insatiable predator: the pump and its filters. It sucks in seaweed fragments, incautious amphipods, copepods, and of course, all the crab and hermit crab babies. I never expect any native-born youngsters in the aquarium; the filters eat them.

Oyster lips and orange-striped green anemones

So I never expected this. I was watching a young hermit, when I saw a crab-like movement underneath an old shell. Crab-like, but too small. I had to get out my hand lens to look at it. And it was a crab! A Baby Crab! Tiny, tiny, really tiny; a new pre-adult, apparently grown from scratch in my tank!

And now, checking carefully under stones and shells, I found two more, one about 4 mm. across, the other a whole cm. across.

The second smallest. Very shy, running away from my and my camera. His "carpet" is a shard of broken abalone shell.

Over the winter, I've brought home a couple of handfuls of eelgrass and rockweed, a blade or two of red algae: it hasn't been a good winter (or spring) for fresh beach veggies. I always check this over very carefully, looking to see what live things have hitchhiked. There were a few tiny periwinkle snails, no hermits, an amphipod or two, and no crabs. And a damaged jellyfish last week, which the crabs ate. That's it.

So maybe, just maybe, those extra three hermits are also home-grown, not three pinhead hermits I'd missed before.

She has something to show me

Three green shore crabs have grown up in my aquarium; two have reached young adult size. They spend most of their time digging under shells and stones, but tonight, one came out and danced for me, showing off her newest acquisition.

She's in berry!

Each one of those little reddish "grapes" is an egg, and there may be as many as 11,000 of them tucked into her abdominal region. She'll be carrying them, tending them, combing and cleaning and fanning them, for several weeks. When they hatch, they will be tiny swimmers for a few more weeks, before the survivors settle on the sand as pinhead crabs.

Only a few will survive, even in the best of conditions. Good thing, or we'd all be drowning in crabs.

(Previous crab in berry posts: Babies,  In Berry (w. video), Mother of thousands.)

They've got their priorities straight

At the bottom of the boat ramp at Beach Grove, someone has laid, long ago, a series of broken paving stones, leading out across the rocks to easier walking on the sand. Every chance I get, I turn over a few of these to see what's sheltered there that day.

This time, among the usual crabs, hermits, and mud snails, I found a pair of shore crabs, either mating, or in the pre-mating holding pattern; belly to belly, male and female in a close embrace.

As I found them, jammed in between stones and shells. The male is on the left.

The other crabs around them scuttled off into crevices between the stones as soon as I removed their roof. These two just stayed put. The male wasn't going to give up his female, and she wasn't in a position to run.

Male crabs select a mature female almost ready to molt; they can't mate while she's armoured with a wide plate across her belly. In the brief moments that she is molting, out of the old shell and unprotected, she may be impregnated. So once he's found a mate, he holds on and doesn't let go until she's ready.

I took a few photos, moving around to get better lighting. Neither crab moved. So I gently eased them out of their cubby-hole. They didn't move, even in my hand. So I placed them on the upside-down paver. Again, neither of them attempted to leave.

The male is on the bottom, this time. Mature males have large pincers and go around posturing with them; "Look at me, look at me! I'm big and I'm dangerous!"

Before they got sunburnt, I slid them off the edge of the slab and back into their cozy hideout. And there, they got down to their interrupted business.

The female is on top this time. A curious hermit - aren't they all? - watches from the bottom of the photo.

The female's apron, the wide abdominal plate, is finally opening. She will be backing out of her old carapace any minute now, leaving the hard forms of legs, eyes, pincers and all behind, taking the soft parts except for her esophagus, stomach lining, and part of her intestines; she'll have to make new ones. And as soon as she's free, the male will impregnate her eggs.

After that, he'll leave; the eggs will develop under her apron, where she'll fan them, clean them, and exercise them until they're ready to hatch, up to eight months from now.

An old video of a mother in berry is on YouTube. (It doesn't work as well as it used to; I'll have to remake it, and a whole bunch of other oldies.)

Discarded finery

Scattered all along the upper levels of Crescent Beach this week, we saw dozens of these crab carapaces:

Helmet crab shell, in shallow water. About 2 inches tip to tip. They may grow to 4 inches.

At first, I thought there had been a die-off, and then I looked more closely. Each one was just the clean upper carapace, unbroken, with no legs or "innards" attached. So it was a general molt, which signals mating time. The crabs come up to the intertidal zone, and the males choose their mate and hold onto her until she molts. Females are not able to mate until they have a new, still soft, carapace.  Within a day or so, the shell has hardened, and the opportunity gone for this year.

We don't usually find these crabs (Cancer cheiragonus) live in the intertidal zone, so this is all the evidence of crabby romance that we will see.

A small collection of sun-dried shells, inside a larger Dungeness crab shell.

I love the textures of these crab shells, especially the pale yellow inner wall of the helmet crab on top. The shell of the Dungeness is quite different, sort of like a stuccoed wall. Click on the photo to see these full size.

Babies, stick-in-the-muds, and Big Blue

It rained or blew all day. I puttered around, doing laundry and other uninspiring chores, and then rewarded myself, playing with my new toy, the little Sony Laurie bought me.

These are more or less random shots from the aquarium (random, in that I pointed the camera at anything that found itself a decent background.) with the camera still set on automatic everything, but without flash.

Ma Crab, in berry again. Showing off the feathery swimmerets that hold the developing eggs.

Close view of the babies. The eggs are transparent, so the eyes are visible.

These photos worked out much better than the ones I was taking with the Olympus, mostly because the camera is so fast and steady; Ma Crab kept moving about, but I was still able to get several decent shots, even this close.

Big Blue

Nothing needed to be adjusted in this photo but the white balance, to cope with the mixed lighting I was using. And, of course, cropping and resizing for the blog.

The small, stay-at-home anemones on the far wall.

The big, wandering anemone. I think he's grown another half-inch since he moved close to the pump.

I did clean this one up, just a bit, to reduce a too-bright light shining through the water surface at the upper left. There's still a hint of camera reflection, which I left untouched, and a few floaters. And again, cropping, white balance, and resizing.

I am more impressed with the camera with every session. So far, it's living up to the salesman's spiel.

Mother of thousands

Ma Crab is skinny again!

Two weeks ago, she was carrying a belly-full of eggs. (If you missed it, the video is "In Berry".) I've been watching her closely these days; every day her egg mass grew, until it was at least as large as her body. She looked awkward and uncomfortable, and didn't move around much. She didn't show any interest in feeding; too busy fanning and cleaning her brood of thousands of embyros.

This morning she had climbed into the top of the sea lettuce, and hung there, spread-eagled, with her apron open as wide as it would go, palpitating gently. She looked miserable. (I had kids; I could relate.)

This evening, I caught her as she cleaned her empty brood chamber. The babies were gone, hatched. And she's got her figure (and appetite) back.

Belly flap, up tight against the body. 

She picked at the inside of the flap for a few minutes, expanding and closing her pleopods, the feather-like appendages that the eggs were attached to. Then she closed up shop; the flap sealed itself close against her body, with a gasket of fine hairs. And off she went to find supper.

Empty belly, showing pleopods.

I've been trying to find the gestation period for these crabs. It's difficult. King crabs can carry the eggs for 11 months. For the green shore crab, I've found sites giving lengths from a few weeks to 8 months. In my aquarium, I saw the eggs barely two weeks before she released the zoea.

But she would have been carrying eggs before I saw them. They would be too small to see, at first. And until the embryos have developed eyes, they are transparent; the pinkish red of the mass came from baby crab eyes.

And the times vary; on the east coast of Canada and the northern US, the crabs have one reproductive cycle per year. Here on the Pacific Coast, as they do in Europe, they produce two broods, in spring and winter. (National Shellfisheries Association, Inc., 2008) The time and length of gestation seems to vary with the temperature of the water, which is warmer here.

And the babies, the zoea? They're swimming. They look sort of like amphipods, but they're far too small for me to see. In the wild, they would drift away to join the plankton off-shore, feeding on tiny particles of organic matter until they have undergone several molts. Most of them wouldn't survive, which is a good thing, since there are several thousands of them. I don't think any will make it in my small tank, surrounded as they are by anemones and barnacles. But I'll be watching for them, just in case.

"In Berry"

Ma Crab was not very cooperative. "But I'm fat!" she says. "And why are you shining lights at my babies?" But she had to come out into the open sometime. Here she is*:

And then she scuttled off to bury herself in the sand.

*Note; on my computer, at least, there is no sound with this set to 360p. Set it to 480p for sound. (Just calm music for a mother-in-waiting.)

We're expecting!

One of my crabs is pregnant. "In berry" is the technical term. I'm working on a video, but it's a slow process. For now, here's the expectant mother, "before":

Green shore crab, female, not pregnant. At least, not "showing".

She was climbing the walls; a perfect position for determining her sex. The white bottom of the abdomen is narrow and triangular in males, wide in females.

I'll have the video ready by tomorrow.