Tuesday, January 11, 2011

Creatures of the muck

It's why I love blogging; other bloggers are so helpful!

After a long day, I was dropping off to sleep at my desk, so I posted my photo of unidentified beasties, and went off to bed. In the morning, I found that Olivia and Tim had done my work for me: the critters are crab zoea! All I had to do was turn to the correct page in my textbook, and there they were. Thanks so much!

Every time we go to a beach bordering Boundary Bay, I collect a 2-litre pop bottle full of nice, clean, fresh, saltwater for the aquarium. I could mix up water and marine salt to the proper salinity, but that would come without the plankton that feeds the anemones and barnacles, and sometimes the crabs and hermits, too. (They love a nice, juicy amphipod, if they can get it.)

In the winter, this is a bit of a problem. In summer, I wade out, at least to knee deep, where the water flows clear. Not at this time of year; the water's just above freezing, and I like warm feet. At the shore line, specially at high tide, or this winter's high "low tides", the water is a thick soup, rich in rotting eelgrass and stirred up mud. So I bring home dark brown muck.

I could filter the water at home, but that would eliminate the plankton, too. (Boundary Bay mud is really fine stuff. I use a double coffee filter, and still some gets through.) So I strain out the big stuff, and let the rest settle overnight. When I pour it off, it leaves a residue that often, even to the naked eye, is hopping with life. This I examine under the lens, with a good light. There's no telling what amazing beasties will show up!

The last bottle of water had a dozen or so of these cute babies:

Crab zoea. Sort of look like birds, don't they?

They wiggled and jittered up and down in the water, mostly staying where the light was strongest. Even under the hand lens, they were hard to see; they looked like two-legged spiderlings. The microscope, at 40x, showed me the eyes, the long spine, the beak-like rostrum*, and the forked tail. *This is just barely visible on the middle baby.

(Yay! The little Sony accepts the homemade lens I used to use on my first camera; with it, I can get a photo almost as clear as what I saw under the 'scope. What fun!)

Drawing from MESA.

I was surprised by this; I didn't expect babies in the chill of mid-winter. Silly of me; a human notion that babies need warmth. I'm continually having to discard these un-examined "rules" for Ma Nature.

But that wasn't all to be found in my bit of sediment! There were a handful of egg-bearing copepods, of the kind that trails the eggs along in one clump at the rear. Most of the ones I see with eggs carry two egg bundles, off to the sides.

Image from here, by Carol E. Lee.

Then there was a baby shrimp, like the three I already have, but so small that under the lens, I could see only the eyes and a hint of transparent body. I didn't try to catch it for a macro; it looked far too fragile to be tampered with.

And this:

Unidentified. About 1 mm. long. Forked tail, two-tone carapace.

I couldn't determine what it is. Another copepod? An infant Nebalia? Maybe; the Nebalia pugettensis are common on this side of the bay.  I found a photo of a Cumella from Bellingham Bay, which seems to match, but I understood that these are more likely to be found in freshwater. Do you recognize it?

The shrimp, the mystery critter, and the copepods went into the tank; the shrimp may survive, but the copepods will soon be lunch. The crab zoea are being raised, at least for now, separately, out of reach of hungry anemone mouths.


  1. Love the animation!

  2. amazing, they are so cute, i always learn so much from you


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