Finding New Uses for Crab Shells in Agriculture - Modern Farmer

Finding New Uses for Crab Shells in Agriculture

Chitosan, found in the shells of crustaceans, is a surprisingly versatile compound that can be used to make everything from fertilizers to food preservers.

Crab shells contain chitosan, a valuable compound with a broad range of applications.
Photography by Krit Kongcharoenpanich, Shutterstock.

We’ve been looking at crab, and other crustaceans, all wrong. Going crabbing for food, digging into the (admittedly delicious) meat and tossing the shell away, all to end up in a landfill or compost pile? That’s just throwing away the most valuable part of the crab, argues Kevin Hammill, CEO of Tidal Grow, a branch of Tidal Vision. The company has gone all in on crab shells. Why? Because of chitosan. 

Found in the fibrous exoskeletons of crabs and other crustaceans, chitosan is a compound that pharmaceutical companies have utilized for years to help with everything from high blood pressure to kidney disease to blood clotting. But medicinal uses are just the beginning for the compound. Hammill says there are “endless possibilities” for what chitosan can do, and Tidal Vision is betting big on its future.

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Based in the Pacific Northwest, Tidal Vision is focused on using materials that would otherwise be discarded. Hammill calls that the “circular economy,” and it’s one where he says everyone should benefit. “In the past, there’s always been winners and losers when bringing in new technology,” he says. “With growers, a lot of times when they’re asked to adopt sustainable practices, they’re asked to give something up.” 

Instead, the company is looking at what can be added to current growing practices to make them more sustainable. They work primarily with snow crabs sourced from sustainable fisheries along the West Coast, from Oregon up to Alaska, to make a product called Tidal Grow, which can be used as a soil amendment or fertilizer. The goal, Hammill says, is to take the crab shell, what would be waste, and remove it from the path to the landfill by upcycling it and giving it new purpose. Since millions of tons of crab, lobster and shrimp shells are discarded every year, that’s a lot of potential chitosan getting tossed out. (Hammill won’t say exactly how many pounds of shells Tidal Vision purchases or offsets from the waste system, noting that’s a proprietary figure.) 

Instead, Tidal Vision synthesizes the chitosan for use in other industries, including water purification, textile manufacturing and food preservation. It’s even used by some winemakers as an antimicrobial agent. Hammill is specifically interested in what chitosan can do for agriculture, where it can be used as a direct seed treatment or in dilutions that are sprayed over an entire field.

Chitosan has been shown to help plants absorb fertilizer better, releasing nitrogen and acting as a biostimulant for the crop, leading to increased yields. Coastal gardeners have long known about the benefits of mixing crustacean shells with leaves, bark and other mulch to make fertilizer. Distilling the compound makes a more potent and more easily absorbed version of this traditional technique.  

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Perhaps it sounds like chitosan is too good to be true—It’s a medicine! A fertilizer! A water purifier!—but Hammill dismisses those claims. Instead, he compares it to other natural compounds that have multiple applications. “Take sulfur, take copper, take phosphate. Everyone thinks of them as plant nutrition, but they’re also a fungicide…every acre of grapes you eat has sulfur on it. We’re so used to these compounds that we forget they have a dual purpose,” Hammill says. “It’s so exciting. And that’s one of our biggest challenges, that there’s so many different opportunities.”

It hasn’t always been so easy to use chitosan. Formulating a liquid or gel-capped product out of the distilled compound isn’t easy to do without access to certain high-tech equipment. However, there are a range of formulations available now, depending on how you want to use it. Chitosan can come in an aerosol spray, a capsule, or even broken down to nanoparticles to inject intravenously (in the case of medicinal use). Hammill says Tidal Vision spent a lot of time coming up with different formulations and application methods to make the product more “user friendly.” Globally, there are other fertilizer brands that take advantage of the compound, and with a wealth of academic research, it’s likely others will jump on board soon.

For Hammill, that’s great news, as there’s more than enough fishing waste to go around. “We’re just trying to help reduce the waste as much as possible one step at a time,” he says. “The more we get this upcycling, this circular economy, the better off we are going to be overall.”

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David Griffiths
7 months ago

We live near the ocean, and through fishing, crabbing and prawning, get a decent supply of shells, prawn heads and fish guts. It all gets fermented with kitchen scraps, etc, in big bokashi vats, and when there’s enough material, I build a thermal compost. All that good stuff should end up in my compost, which I use to start seedlings and refresh my garden.

Otis Needleman
7 months ago

Great! The fertilizer will especially be needed. Just wonder how much they are talking in the way of shells; the number of millions of tons must be a world-wide number.

7 months ago

I just wrote a paper on this for my agriculture and biology classes, but my paper was more geared towards the chitin produced by mushrooms! Very cool that this is becoming more mainstream!

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