Srevotfel, redux

A month's worth of aquarium pix; the odd shots taken while I was stalking something else.

One of the smaller hairy hermits, wearing a live barnacle on his shell. On Barnacle Mountain.

Young proliferating anemone. They live on their mother's column until they feel ready to leave home, then detach and float off to a new site. There are about half a dozen scattered around the tank, and another few still clinging to Mom.

Flatworm on the wall, carrying a small snail. Supper's cooking!

Making a snail taco.

A mouthful of snail meat. The shell has been dropped. A new outfit for a small hermit!

One of my tiniest hermits. These are sometimes orange, sometimes dark brown and white. I don't think they're hairies; they don't get much bigger than this.

Face shot of a small red shrimp

Snowy, again. Growing up, getting braver. His eyes are green now, his body a bit speckled.

Snowy molted. And I found his carapace before it crumbled.

I've been trying to determine his species; it's difficult, him being so small and so elusive. So I was glad to get an entire carapace, to see the shape and count the teeth. And I'm still not quite sure, but I think he's a baby red rock crab.

The carapace of adults is deep brick red in color and has 5 teeth that protrude anteriorly between the eyes.  Nine teeth that line the edge of the carapace lateral to each eye have a somewhat fluted appearance, like pie crust.  Carapace shape has been described as being fan shaped or shaped like the letter “D”.  The pinchers have black tips.  Juvenile red rock crabs are quite variable in carapace color and pattern, the patterns sometimes being quite exotic. (WSU BW)

5 teeth between the eyes: check.
9 teeth along the edge: probably; hard to see clearly.
Fan-shaped carapace: check. It's bumpy, too; the Dungeness crab has a smooth carapace.
Black-tipped pincers: looks like that's where he's going; there's a faint purplish tinge to the tips now.

Small bubble shell, wearing green algae.

Limpet, pooping.

Every batch of eelgrass comes home with a fair number of limpets, mostly quite small. They trundle about, cleaning the eelgrass, cleaning the walls, sometimes sleeping for a day or two. As long as they stay stuck to anything, they do well; if at any time they lose their grip and fall to the sand, they are eaten within minutes. The hermits hold them in one pincer, open side up, like a bowl of stew, picking out the meat with the other pincer.

With a sea star or two in the tank, things change; only on the eelgrass are they safe. Wherever the sea star can get a solid grip, he can rip the limpet away from his base. This large one (above) only lasted a few days.

Fashion statement

Ma Shrimp, now that she's done with raising a family, has become quite the flashy dresser. These days, she's showing off a slinky, speckled skirt, green and black, with white stripes and a black and grey lacy frill down the front; striped leggings; a green and yellow patterned coat. And I love her new vest!

Sitka shrimp

As she was, back when she had youngsters to deal with:

In berry, last May

The other three shrimp that came home with her have all turned red as they grew, with the largest being the reddest.  All four are semi-transparent against a bright light. In the wild, that gives them double-duty camouflage; they're dark and mottled, as a fish would see them from above, and blend into the patterns of the sea floor. Seen from below, as by a crab, they match the light from the sky.

Puzzling over colour schemes

Back in May, I brought home four small Sitka shrimp; three tiny transparent slivers of glass with eyes, and one larger one, greenish, with her eggs.

Ma shrimp, in berry, last May. Green, mostly.

With time, and a good diet, she has turned mostly black, with a white, blotchy saddle. It makes for good camouflage, and poor photos; the camera never knows where to focus.

The other three grew, and started to change colour. One now is a pale bluish pink, one sort of greenish, and the third is a bright red, with white polka dots and blue flags.

Big Red, resting on sand.

And this colouring works as camouflage, too; it's rare that I catch this guy against a contrasting background. Here's a photo where I caught him just emerging from his normal hideout:

Not so easily seen, almost invisible if he's deep in the seaweed.

These shrimp can take their colouring from their diet; Big Red has been eating dark red bladed algae, and things he finds in the red filamentous algae. But the other three have been living in the same tank, probably eating the same things, and yet they are black, green, and bluish.

I have studied details of the camouflage coloration, in which several patterns occur, all forms of disruptive coloration, in which stripes and splotches break up the outline of the shrimp, making it difficult to recognize when viewed against a background which is variable in color and tone. The disruptive coloration is a defense against visually-hunting predators such as shorebirds and intertidal fishes. ... 

Color patterns are poorly expressed in juveniles and small males, rendering them transparent, which is another way to appear invisible to predators using vision. This doesn't work in larger individuals, especially females, since the internal organs and incubated embryos destroy the transparency "trick"; camouflage color patterns then come into play. (From Raymond Bauer, Shrimp researcher.)

Questions, questions. Are the shrimp in the tank choosing different food sources? If I took away the red algae and added only greens, like sea lettuce and rockweed, would Big Red turn green? Where is Ma Shrimp getting her black colouring from? If food was scarcer, would she turn transparent again?

Bauer says that Sitka shrimp lose most of their colouration at night; in a tank, where the lighting is either on or off, the shrimp starts off his day transparent, or nearly so, and 15 minutes after the light is turned on, he's back to normal.

I just went back to my tank; Ma S. is still black, now in the middle of the night. I couldn't find any of the others. But there's still a bit of light, from my screen at the far side of the room. If I work somewhere else, will she disappear?

I'll have to try that.

Two very tiny, completely transparent shrimps hitchiked home with me last week. I can only see them if the light happens to hit them at the right angle, against the right background. I wonder what colour they will turn out to be when they grow up.

It must be quantum

Shrimps don't swim. Fish swim, so do amphipods, worms of all sorts, jellyfish, and eelgrass isopods. Even a crab will swim, if need be, downwards, with panicky, uncoordinated flailing of skinny legs. But shrimps don't swim.

They drift. They hang in the water, not moving, holding onto a blade of seaweed. They let go, and drift slowly in the current. Sideways, upwards, backwards, forward; it makes no difference to them which way they're facing.

Then, suddenly, they discover modern physics and execute a quantum leap. You were looking straight at one, and then, without any intervening movement, it was 'way over on the far side of the tank or tidepool. You never saw it go; it was just gone.

It doesn't help that as often as not, it was transparent, or nearly so, to begin with.

Four shrimp came home with me last week. Three are tiny, 1/4 to 1/2 inch long, and transparent, except for the eyes. If the light is right, they're like shards of greenish glass.

The larger one is visible, mostly because she's been eating well. And because she's carrying a load of eggs. At least they're a decent colour.

Sitka shrimp, 1 inch long, with babies. Colour saturated and darkened.

The green and brown solid mass in her cephalothorax and along her spine is mostly her digestive system. When food is scarce, it shrinks. When the food is digested, it moves along the spine and out the anus, visible all the way.

The eggs are held under her abdomen with her pleopods (aka swimming legs); she is constantly tending them with her walking legs.

Click on the photo to see it full size; now you can see the pattern of red and blue dots on her carapace, and the long, sawtoothed blade (the rostrum) stretching out from the top of her head.

Top view, in a white tray, with no place for her to go. The eggs are visible through the whole thickness of her body. (Saturated and darkened again.)