On April 24th, 2017 we learned about

The many ecological rewards of sowing edible seaweed

“Where does seaweed come from?” my four-year-old asked, while stuffing crispy nori snacks into his mouth.

It seems like an obvious, I mean, it says “sea” right in the name, but he’s four, and I realized that beyond saying “the ocean,” I couldn’t really explain much more than that. I could picture kelp forests that were home to various other plants and animals (“like in Finding Dory!“) but really had no image of how humans harvest the stuff. Which, it turns out, they’re doing more and more all over the world.

The first thing about seaweed is that it’s not really a weed, because it’s not a plant. There are folks out there who try to frame it as a vegetable in order to make the idea of cooking it more approachable, but edible kelp is a form of multicellular algae. Being algae is actually part of what makes growing kelp so cool, because it happily gobbles up nitrogen and carbon dioxide out of the water. On the negative end of the spectrum, excess nitrogen, such as from fertilizer runoff, can cause very harmful blooms of algae, such as with “red tides.” Brown kelp like oarweed (Laminaria digitata), on the other hand, can take that nitrogen and make it into something tasty and nutritious. The fact that it essentially cleans up the ecosystem and increases biodiversity just makes things that much more appealing.

Farming among fish

To raise seaweed, a lot of farmers around the United States are looking at methods that aim to minimize disrupting local ecosystems. Kelp can be grown along pre-spored wires suspended in the water. In “3D” farms, the seaweed is then raised alongside other seafood, like clams and mussels. This allows for a lot of healthy biodiversity in a small footprint, requires no real “inputs” from the farmer in the way of fertilizers or water, and leaves a space that can still be used by recreational fishermen and swimmers. The presence of shellfish means that water quality is tested frequently, so the kelp is a lot more pristine than it absolutely needs to be. In other scenarios, kelp is being raised not for food, but as a sort of remediation device, sucking up heavy metals in water supplies where no food can be raised.

Seaweed has been harvested to some degree since at least the 17th century, but new uses for the algae are making it a very popular crop these days. While farmers struggle to keep up with orders, it’s important to remember that not all production is equal. In some places, farmers are following in the footsteps of their terrestrial counterparts and tearing out native species to accommodate their cash crop. For seaweeds, people are usually removing mangroves and eelgrass, which ends up lowering water quality on top of reducing biodiversity.

Pick and process it

So to get back to my kid’s question, seaweed is farmed in the ocean, either to be eaten, clean the water, or make a variety of other products from biofuels to personal lubricants. On a small scale, you can simply cut off a single blade (the leafy bits) or the central stalk— just take care not to cut too close to the holdfasts so the alga can keep growing. On a larger scale, rent some shoreline and be ready to haul out multiple tons of the stuff on a regular basis by hauling your lines out of the water.


My four-year-old asked: Does cutting the seaweed hurt it?

It does stop that section from growing, but I think the real question here was about if a non-plant feels things like sentient animals do. Some algae do have photoreceptors, but as far as I can tell, farmed brown algae doesn’t have any nervous system it could use to sense or experience the process of being harvested.

Source: Kelp For Farmers: Seaweed Becomes A New Crop In America by Craig Lemoult, The Salt

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