Sunday, August 22, 2010

In the holdfast: feathers, spines, eyes and ... mustaches?

When the tide is at its lowest, we try to be there, to walk out to the far edge and wade in the eelgrass beds or scramble over the weedy rocks. Here the shore critters thin out, giving way to those that like deeper, colder water; here the big crabs roam and the geoducks spit at us as we walk. There's a line where the starfish start, a sunfish level, a nest of kelp crabs waving pincers at the careless hand, fish and sand dollars.

I always wade in, looking out at the deeper water, where the kelp grows. I can't go there. The swaying forest with its multi-species community is always just out of reach.

But at high tide, on windy days, the tables are turned. The waves rip up boatloads of kelp and eelgrass, roll them up like carpets, and toss them on the dry shore for me to poke at. I search the eelgrass for isopods and snails, the kelp for bryozoans and flatworms, or maybe even a nudibranch or two. This week I left the blades of kelp alone and we collected small holdfasts.

Holdfast, somewhat sun-bleached.

A holdfast looks like a root mass, but it doesn't gather nutrients. It's function is to hold the kelp down. At the far end are the long fronds, and the floating bladders; without a good anchor, the kelp is at the mercy (none) of the waves. The holdfast is tough and strong; it grabs onto rocks at the bottom, where it may stay for up to seven years. It's an ideal hiding place for small creatures, an interface between sea floor and live plant, a food source and a hunting ground. I wanted to see what lived there.

At home, I dumped my holdfasts into a bowl of fresh sea water, and gently pried and cut them apart. (Even the thinner stems are as tough as green wood.) Quite a few dead amphipods and skeleton shrimp floated off; it had been a rough trip, from sea floor to rollers to dry shore and sunlight, then to a plastic bag in the trunk of a car.  And the centre area, inside the teepee of "roots" was full of broken barnacle shells, the barnacles eaten away.

But then the worms came wriggling out. First, the polychaetes:

Small polychaete with an almost-human face. Love the moustaches!* And a live amphipod.

There were quite a few of these, mostly small; under a couple of inches long. And another few scale worms, which I had not seen before.

15-scaled worm, Harmothoe imbricata. I counted the scales, 15 per side.

Another 15-scaler, about an inch long.

Look at the upper end: each scale is like a sequin, circular. In these, one arc of the circle is black, which makes the pattern down the back. It is the same species as the one above, though.

And look at that little tentacly thing. That's what held me up; I couldn't identify it.

A better view. Notice the black dots on the central stalks of the "feathers".

I looked for others in the holdfasts, and thought I saw a tiny one like this, but with a stalk. I missed it, trying to fish it out, and never found it again. But there was something similar, fixed on the holdfast:

Hmmm ... Cnidarian, said my granddaughter.  Tubeworm? said I. Not in my book, whatever it is. About 1/4 inch high.

What else? There were a half-dozen mussels jammed in between the "roots", umpteen sand-grain-sized, black snails, many little brown isopods, several clams:

It looks like a geoduck, but it's barely a centimeter long, siphons and all. And it was the largest.

And loads of tiny green sea urchins:

Green sea urchin, Strongylocentrotus droecachiensis. With three black snails.

Sea urchins thrive on kelp, in such numbers that they are capable of killing an entire kelp forest if not kept down by other predators, such as sea otters.
Both sea otters (Enhydra lutris) and sea urchins (Strongylocentrotus spp.) play critical roles in the stable equilibrium ecosystem. Sea urchins graze kelp and may reach population densities large enough to destroy kelp forests at the rate of 30 feet per month. Urchins move in "herds," and enough urchins may remain in the "barrens" of a former kelp forest to negate any attempt at regrowth. Sea otters, playing a critical role in containing the urchin populations, prey on urchins and thus control the numbers of kelp grazers.
From NOAA.
The ones that came home with me are too tiny, as yet, to have done much damage. Now they're in my aquarium, in the remains of one of the holdfasts; they can eat that, for now.

Tiny, unusual shell. No snail inside. Checkered hairysnail, Trichotropsis cancellata. Eats leftovers from calcareous tubeworms.

And I was still wondering about that spiral of tentacles. I couldn't find it anywhere on the web or in my books. I decided, last night, to search again; I washed the bits of holdfast that hadn't gone into my tank thoroughly, again, shaking and prying at the stuff stuck in cracks. And I found these:

Feather duster worm. I don't know what species.

Same worm, different angle. This was about an inch and a half long.

I found several more, smaller and much smaller. The tiniest, I picked up in an eye-dropper:

Very much alive, and waving about.

So I'm thinking that the mystery "flower" (as Laurie calls it) is probably the plume of a feather-duster worm, broken off. I couldn't find its match in the Encyclopedia, but reading every description, I discovered another clue: some of these feather-duster worms have small eyes on the spine of the branches (radioles). The twin-eyed feather-duster, Bispira sp., for an extreme example, may have as many as 1,000 pairs!

Here's that photo again:

Are those eyes?

I almost forgot: there were also at least three flatworms, so tiny they were just pale brown specks that wandered around when I put them in a plastic cup with a few teaspoons of water. They're in the tank, now; competition for the two big ones that were already there.

*Reminds me of Yosemite Sam.


  1. There's a whole world in a holdfast.

    A fragment of feather duster worm sounds like a plausible explanation for the feathers. Bits of animals are always tricky.

  2. How fascinating to think that much life came out of the holdfast. Very interesting post.

  3. All I can say is your photographs are amazing! Such a wonderful collection of tiny life. - Margy


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