Who’s at Home in a Holdfast?

A kelp holdfast - home sweet home?

A kelp holdfast - home sweet home?

by Erin Loury, Ichthyology Lab

Erin Loury

Erin Loury

I got to play evil landlord the other day and evicted a bunch of little critters from their home (proving that even marine invertebrates are not immune to housing woes…).  I was on the hunt for some specimens that might be prey items for the gopher rockfish, which I’m studying for my thesis.  Someone suggested I seek out the creepy crawly snacks where they live – holed up in a kelp holdfast.

A whole mess of tenants

A whole mess of tenants was living inside!

A holdfast keeps a towering kelp plant anchored firmly to the sea floor.  It may look like a giant root ball, but its many fingers don’t suck up nutrients and water like true roots do in land plants.  They do, apparently, make a great high-density high rise for little crabs, brittle stars, and more.

While hacking open the basketball-sized mass of slippery tubes, I expected to find maybe a dozen animals or so – but I tallied up some 85 residents! Crabs, brittle stars, polychaetes (worms), urchins, shrimp, you name it.  I was so jazzed to dig up a handful of these little peanut worms (also called sipunculids).  They have a long proboscis that they can actually turn inside out and tuck up inside themselves!  And aren’t they just so fat and cute?

Peanut worms turning themselves inside out

Peanut worms in a jam

What do you think makes a holdfast such a great home?  Post a comment and let us know what you think!

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5 Responses to Who’s at Home in a Holdfast?

  1. jannet says:

    I’m curious..about how tall do these holdfasts grow up to be?


  2. Erin Loury says:

    Hi Jannet, thanks for being curious! I had to consult with my phycology (algae-studying friends) on this one. The holdfast of the giant kelp can actually grow to be 1 meter (or 3 feet) tall! New branches grow down over the outside of the old ones and give it a cone shape. I’m not sure how wide they get to be at the base, but my friends say at least a couple of feet. The one I cut into was pretty small by comparison, but it gave me what I needed!

    What’s also cool is the size of the actual kelp plant that the holdfast supports – the stipe, (or “stem”) of the giant kelp can grow 45.7 m (or 150 feet) long! That’s as tall as the Statue of Liberty – and the kelp fronds can extend the length of the plant even more. No wonder they call it a kelp “forest!”


  3. Judith Sanderson says:

    Hi, I am a high school biology teacher in Culver City, So. Cal. and every year since early ’80 I get holdfasts for all 5 class periods to fill out the Ecology unit…biological community, niche, feeding relationships, but it would be so helpful if I could find a write-up on holdfasts that gave names to more common inverts and some natural history. I have been piecing it together, but think their must be some great source out there? And of course every year the community is different. One years loads of tube worms, another year it’s brittle stars. Current supplier is Monterey Abalone Co. For a long time Rimmon Fay got them for us (the only honest member of the Coastal Commision!) Ah, those were the days. Thanks for any response. Judy Sanderson


    • mlmlblog says:

      That is fantastic that you involve all of your classes in marine science! I personally use Gotshall’s Guide to Marine Invertebrates: Alaska to Baja California for quick identification of common invertebrates. Every entry has a photo of the animal and some natural history information. Another, more comprehensive, book is a classic called Intertidal Invertebrates of California by R.H., Abbott, D.P. & Haderlie, and E.C. Morris. It is out of print now, but you can still find it for sale online. I hope this helps, and always feel free to send your students to our Ask a Grad Student… page if they have trouble identifying something, or email us a photo and we’ll try to help as best we can.


  4. Pingback: A Pack o’ Peanut Worms « The Drop-In to Moss Landing Marine Labs

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