Holdfast

By The Marine Detective on October 7, 2020

Have you wondered about what holds down an underwater forest?
It’s the holdfast.

I spent the majority of a recent dive in a sun-soaked Bull Kelp forest. My hope was that the photos I took would communicate the role of the holdfast AND the stunning beauty of being in such forests.

Kelp does not have roots. Rather the algae / kelps get their nutrients through the fronds (leave-like structures) and it is the holdfast that anchors kelp onto rocks.

It’s  a tangle of woody structures that you may have seen washed up on the beach.

You can imagine how strong the holdfast has to be to withstand the buoyancy of the waves, current and the kelp’s floatation (the gas-filled pneumatocysts). The two photos below show how the buoyancy is greater than the mass of the rocks whereby the rock cannot anchor the kelp. 

If rocks are too light to counter the floatation of the pneumatocyst and/or the force of waves and currents, the kelp will change the ocean bottom by carrying away those rocks. You might see these holdfasts, still attached to the rocks, when they wash ashore.  

There you go – a daily dose of depth for you. 

It may be that knowing about holdfasts and their rocks is of particular value in these stormy times.

Holdfast dear readers. Holdfast.

Added January 2024, research into the age of holdfasts.

• Kiel S, Goedert JL, Huynh TL, Krings M, Parkinson D, Romero R, Looy CV. Early Oligocene kelp holdfasts and stepwise evolution of the kelp ecosystem in the North Pacific. Proc Natl Acad Sci U S A.
  NPR podcast, January 22, 2024,  New kelp fossils may help explain the Pacific Ocean’s underwater jungles
• Times Colonist, January 28, 2024, B.C.’s kelp forests more ancient than once thought, study finds – Kelp fossils found in the Olympic Peninsula suggest the marine ‘forests’ are more than 32 million years old, double previous estimates

---

My additional blog items on kelp include:

• What on Earth is “Alternation of Generations”?
• Enough Carbon Monoxide to Kill a Chicken ?
• Every Breath You Take . . . .
• Holdfast
• Journey Through Kelp