There are numerous ways to grow numerous types of seaweed. I won’t pretend to know them all nor the several thousand varieties of macroalgae.
That said, a particularly common method involves cultivating seaweed on longlines, or growlines, suspended in the water. This technique works well for species including sugar kelp (saccharina latissima), which is what I aim to grow.
Sugar kelp is endemic to Massachusetts and valued for its edibility/nutrients, bioremediation and carbon sequestration capabilities, and more. Below, I’ll refer to the seaweed as ‘kelp,’ and give a simplified explanation of the longline/growline process. This explanation imparts the elementary understanding I had when I decided to give seaweed farming a go.
Note: Although “longline” appears to be the dominant terminology, I dislike the word because it conjures an image of savage fishing rigs dragging miles of baited hooks, catching and killing indiscriminately. The term growline avoids this and seems more accurate.
A growline is made of rope. It is suspended horizontally a couple meters below the water's surface, between vertical lines that are anchored to the seafloor. Together, this gear is referred to as an "array." Kelp seed is attached to the growline, the kelp dangles and drifts in the water as it grows, and the mature kelp is removed/cut from the line at harvest.
Nursery Phase: The kelp seed begins its life in a lab. In this seminal stage, when the kelp goes from microscopic seed to ~1 mm, the lab environment provides optimal conditions for maturation; free from contamination, damaging temperatures, and competing microorganisms (damn those protozoan grazers). The kelp matures in tanks of water, on string wrapped around PVC tubing, creating a “seedstring” on a “seedspool.” After approximately a month of growth, the seedstring with its not-quite-baby-kelp moves from the comforts of the lab to the growline at sea.
<aside> 💡 For a more detailed explanation of the nursery phase, check out this article from the University of Rhode Island: Nursery Phase: The Journey Of Kelp From Spore To Seed String To Sea
To absolutely nerd out on the nursery phase, read the New England Seaweed Culture Handbook – Nursery Systems, published by University of Connecticut Sea Grant.
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Growline Phase: Sugar kelp is a winter crop. Between November and December, the seedstring will be attached to the growline by wrapping it around the growline rope. Come April-ish, the kelp will be harvested by cutting it off of the growline. Between November and April, no additional inputs and minimal work is required – outside of requisite maintenance on the arrays to avoid system failures. Seaweed cultivation doesn’t require fertilizers, pesticides, or freshwater. This is part of its appeal and a major advantage over terrestrial crops.
Harvest & Processing: What do you do with the harvested kelp? The specifics will depend on the intended use: food or non-food. In general, the kelp will either be minimally processed (sold fresh or frozen), or dried and possibly milled, to be used as an ingredient in anything from kelp burgers and super-nutritious beverages to fertilizer and bioplastics.
Note: There appears to be an interesting opportunity to fill the role of “middle-person,” between seaweed farmer and seaweed users such as chefs, engineers, entrepreneurs, and the like, who use seaweed/seaweed extracts as an ingredient in their creations. Bolstering this part of the supply chain could provide farmers with more consistent and higher volume buyers, as well as build a supportive network between farmers, market partners and regulators. The Crop Project, a USA-based startup with a mission to bring regenerative crops to market, is doing just this.
⏮ Climate Sprint / Seaweed Policy / Learning By Doing
⏭ Partnering Up / Shallow Water / Greenwave
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