Sunday, December 02, 2012

Critters in my hard drive

On yesterday's post, Sara Rall said, in the comments, "I never knew there were so many intertidal creatures." Nor did I; I'm still constantly surprised by what turns up on the beaches.

And I have a new one tonight. This critter is a main component of the diet of the sandpipers and other peeps that feast on the mud flats.

I found one in my aquarium a year ago last May and couldn't identify it at all.

Here's my description from back then:
I discovered this beastie in a worm tunnel in my aquarium a week ago. It sort of looks like an amphipod with eggs, but stays in the tunnel like a worm, only sliding up to the surface of the sand, then down again every so often.The legs at the top look like they belong to a spider. At the bottom end, almost transparent appendages flutter constantly, again like an amphipod or the shrimps. I think there may be more than one in the tunnel. They, or it, don't match any of the green amphipods in the tank; it's longer and thinner, and leggier.

Corophium (salmonis. spinicorme, or possibly stimpsoni)

 Hugh, of Rock, Paper, Lizard, identified it as an amphipod, of the Genus Corophium*, maybe salmonis. He posted a link, which led to an identification page and a few photos of details which I had no hope of seeing on my critter. Wikipedia had (has) nothing on them; even Google gave me no results. And there the matter lay.

And all the time, I had photos stashed in my hard drive that would have helped. Now, sorting and rescuing, I have discovered them. They're from a year farther back, in April of 2010. In a clump of eelgrass brought back from Boundary Bay, I had discovered a series of tiny wriggling things, mostly worms, mostly unidentifiable from my photos. I had done my best with them, uselessly, and stashed the photos for later, then forgot them. Now I've started working on them again. And the first in line were the Corophium that I had been puzzling over last May.

Definitely tiny; here's one in an eye-dropper

It's an amphipod, but unlike the ones I see all the time.

Long, long front legs and antennae.

Photo of Corophium salmonis from the San Juan Islands. Photo by Michael R. Clapp/

These tiny amphipods (also called "mud shrimp", though they are not shrimp) live in burrows like worm tunnels in intertidal waters. They are adaptable, so can tolerate the varying conditions; high salinity in the salt marshes, dropping to almost freshwater levels after heavy rains; temperatures from bathtub warmth to freezing; sand and wave movement. They feed on the biofilm that grows on fine, silty sand; the Boundary Bay/Mud Bay flats are ideal for them.

The birds know this. A sandpiper can eat thousands of these tasty morsels in an hour, running along the beach following the retreating tide, peck, peck, pecking. At what? I have wondered. The worms lie deeper, but mature A. salmonis females wait at the mouth of their burrow for cruising males; both easy prey, and fat.

When the tide comes in, young salmon and other fish take their turn. There's plenty for everyone. Those apparently barren sands are teeming.

There's a very interesting article about Corophium on the east coast of Canada, here. It looks at a different species, but much about their lifestyle and predators will be the same.

*aka Americorophiuim.

Updated to correct Genus name, broken links, 2015.


  1. I have started wondering, after a few months of reading your blog, if I will feel as happy about walking on a sandy beach as I used to. I had never thought about the tiny animals I was walking on...
    Love some of those sky photos! Isn't exploring the hard drive fun!!

  2. Judy, I think of that, too, walking across acres of mud snails on the beach. I try to aim for bare spots, but can't avoid hearing the occasional "crunch". Crab food, I think. At least the crabs won't be trying to pry one more live snail out of his shell.

    As for the smaller critters, the amphipods and worms, as the tide goes out, they retreat farther under the sand. This is why sandpipers are usually hunting just at or below water's edge as the tide drops; behind them, the animals have gone too deep for them. So you can walk without worries.

    Underwater, if you're wading, of course the sand is more fluid, and stepping on a burrow only pushes it aside. No harm done.


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