Beachcombing in the winter can lead to the discovery of a variety of treasures. Fragments of clamshells, driftwood, and sea glass are among the usual suspects. Then, there are the rare treasures like a whole sand dollar or sea urchin that have somehow survived being tossed ashore. But often it is the strange combinations of things that truly catch your attention. On a recent beach trip, one of my daughters came across a kelp holdfast entangling a blue mussel shell. It had the look of an uprooted tree that had taken a fieldstone with it, its many wiry tendrils enveloping the shell.

The odd thing about kelp is that this holdfast isn’t a root at all. That’s because kelp is a type of seaweed and seaweeds are actually algae and not plants. That means that they absorb nutrients straight from their surroundings, not from the ground, or whatever they are attached to. This is a prime example of an adaptation to the marine environment where nutrients are all floating around, whereas, on land, those same nutrients are concentrated in the ground.

So, why do seaweeds have holdfasts then, if it isn’t to gather up nutrients? Unlike free-floating algae that are teeny and short-lived, seaweeds like to stick to one spot where they can grow. But, that “sticky” spot can be almost anything. Often, it is the rocks along the shore. But, other times, it can be a pier, a sunken object or a clump of old shells.

When seaweed does attach itself to something, it does so with some impressive strength. This isn’t just by growing what looks like a root bundle around an object. Seaweeds also literally glue themselves down. It starts when they are tiny baby plants or spores. These spores find a spot to land and then produce a sugary substance that is super sticky. In fact, scientists have tried to mimic these marine glues for industrial purposes because they are so strong. From this glued spot, the seaweed then grows its tangly holdfast as well as a stem, or stipe, and fronds to absorb sunlight.

While holdfasts don’t function like roots by absorbing nutrients, they do have some similarity to trees in that they comprise a part of the seaweed that is capable of re-growing, much like a tree can regrow even if some of its branches are cut. This is important for seaweed because, like trees, seaweed is a harvestable resource.

Several species of seaweeds are harvested for a variety of uses from fertilizer and animal food to thickeners in ice cream and toothpaste and, of course, straight up. Seaweed is becoming an increasingly common food taken just for what it is. It can be sprinkled on top of just about anything as a kind of salt substitute, pickled as in seaweed salad, or used to flavor a soup broth. There are lots of great companies in Maine harvesting both wild seaweed and growing their own through aquaculture. The holdfast and lower portions of the seaweed are important in determining a sustainable method of wild harvesting. Maine law requires that rockweed be cut at least 16 inches about the holdfast and above the lowest lateral branches, thus leaving some “leafy” parts to gather sunlight and regrow.

Next time you are beachcombing, take a look for one of these holdfasts and check out what the seaweed has chosen as its sticking spot. You might even see some of the sugary glue residue as well, a truly impressive feature of these seaweeds that are a sometimes-overlooked coastal resource.

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