Can seaweed save the day? Scientists aren’t sure

In the waters just off Canada’s west coast, Amanda Swinimer harvests wild kelp, either from the shoreline when the tides allow, or further out among the waving underwater forests of bull kelp.

Once dried, it’s sold to individual customers and restaurants in Victoria, the capital of the Canadian province of British Columbia.

This small-scale trade has been her livelihood for more than 20 years. But in 2019, a formidable new competitor entered the market.

Cascadia Seaweed, an agtech startup backed by millions of seed funding, announced its ambition to create a multi-billion-dollar seaweed farming venture along the coast.

For Swinimer, who knew of only a handful of other small kelp harvesters in her area at the time, the news came as a shock.

“Seaweed went from this incredibly niche thing to the media telling everyone it’s going to save the world from climate change,” she recalls.

There is some truth to that claim. Seaweed is an environmental multitasker that enhances marine biodiversity, sequesters vast amounts of carbon and can even combat ocean acidification.

Each year, kelp forests remove an estimated 4.91 megatons of carbon from the atmosphere and offer ecosystem services worth around USD 500 billion.

In other words, the humble seaweed isn’t just a nutritious food or useful gelling agent – it’s a formidable nature-based solution that’s gone unrecognized for far too long.

But that’s now changing, and it’s attracting the attention of the media, as well as scientists, materials engineers, investors and companies hoping to farm the oceans.

The state of seaweed

In 2022, the world farmed some 36.5 million tons of seaweed and micro-algae – an industry worth USD 5.6 billion as of 2020.

Seaweed is currently farmed in at least 56 countries across all continents, but 99 percent of global production takes place in Asia, where it is used primarily for food.

In 2018, Organization for Economic Cooperation and Development (OECD) countries accounted for over 60 percent of the total export value of seaweeds “traded for direct human consumption or as raw material to produce other food or non-food products.”

Seaweed could potentially be grown and harvested over 650 million hectares worldwide, according to a 2023 study.

But despite its potential benefits for carbon sequestration and ‘blue carbon,’ scientists are cautious about cultivating seaweed on a grand scale.

“As with any sort of cultivation of wild species, it becomes a risk to have these genetic strains that are being farmed close to natural populations,” says Amelia Hesketh, a post-doctoral fellow at the School of Resource and Environmental Management at Simon Fraser University.

“Then you get mixing of genes between the two, and that can lead to some unintended outcomes where we’re essentially polluting.”

Hesketh can’t help but compare this new ‘seaweed rush’ to a previous craze for salmon farming.

Once touted as a way to take pressure off wild salmon populations, it instead became a problem as escaped fish interbred with their wild counterparts, diluting the gene pool, and infected them with sea lice and other diseases.

Scientists have flagged another concern: will all this seaweed actually sink to the sea bed as it’s supposed to, or will it float on the surface and smother other plant life beneath it?

“There are also some studies that suggest that if you are cultivating kelp really intensively, it may start to compete with the phytoplankton communities for light and nutrients in the water,” Hesketh adds.

Phytoplankton serves as a primary food source that feeds almost all oceanic organisms directly or indirectly.

Cascadia recognizes the many unknowns. It’s now farming kelp over 40 hectares in partnership with five First Nations communities, which it sells in the form of liquid soil supplements and cattle feed additives to reduce bovine methane emissions.

The company’s head of science, Jennifer Clark, says it’s difficult to quantify how much seaweed actually contributes to long-term carbon sequestration. That’s because other organisms and bacteria break down seaweed and release that carbon back into the environment.

Along with several other seaweed farms, Cascadia participated in a study by the nonprofit Oceans 2050 – one of many trying to find answers to those thorny questions. The results are expected to be published later this year.

The risks to marine ecosystems from large-scale seaweed farming are also hard to quantify. But given the mounting climate crisis, Hesketh believes these concerns are often being dismissed “to pivot our economy towards something more environmentally friendly.”

Seaweed seat covers and biofoam bras

Seaweed isn’t just useful for capturing carbon. It could also eventually replace the tons of single-use plastic waste choking rivers, polluting the oceans and piling up on land.

At Amsterdam-based startup Kelp Blue, materials engineers are extracting the polysaccharides in kelp to create an array of materials, including kelp leather for car seat covers and biofoam for use in everything from bras to furniture cushions.

It also makes a fertilizer called StimBlue+, which it says helps farmers boost yields while also reducing the need for chemical inputs.

Kelp Blue is currently farming around 35 hectares of giant kelp (Macrocystis pyrifera) off the coast of Namibia, adding one to two hectares each month, and it has a license to expand that up to 6,400 hectares. It also has licenses in New Zealand and Alaska totaling another 800 hectares.

Valentin Pitiot, the Dutch startup’s head of agribusiness, likens their work to “going into the desert and planting an oasis.”

“Macrocystis recruits all kinds of different types of organisms – other seaweeds, fish, vertebrates, invertebrates, everything – and creates a forest,” he adds.

Meanwhile, Germany-based Smartfiber is manufacturing fibers from sustainable seaweed sourced from Iceland, which can be spun into biodegradable yarns and textiles.

So far, clothing brands have only been using Smartfiber’s fibers in small collections, partly because they’re more expensive than synthetics or cotton, says company spokesperson Nicole Ring.

“The question is,” she points out, “how much money am I willing to pay to buy one good garment versus three made with synthetics in Asia under poor working conditions?”

Perhaps one of the most promising uses for seaweed is as a replacement for plastic packaging.

The Natural Polymers Group is a coalition of eight startups making consumer goods from bioplastics. Their shared mission is “to establish nature-based materials as credible, mainstream solutions to replace plastic products, contributing to a cleaner and healthier world.”

But because the global packaging industry has been geared towards plastics for over a century, this innovative sector faces significant hurdles in scaling up. For instance, there are relatively few production facilities for bioplastics, resulting in higher production costs.

At the same time, seaweed-based products are yet to be made compatible with existing plastic-making machinery. That means bioplastic manufacturers need to build their own machinery while also competing on speed and cost.

Unknown unknowns

While there is growing academic interest in seaweed farming, there are still plenty of questions that have yet to be answered.

“The study of seaweed and kelp has really taken off in the past five to 10 years, so we will get to the point where we understand it better,” says Hesketh.

“But I think in some cases, we’re putting the policy a little bit ahead of the science at the moment.”

And while the UN Global Compact’s seaweed manifesto supports large-scale production of seaweed, it also points to the need for harmonized and specific policies, standards and regulations to do so safely.

However a position paper from Seaweed Commons, co-authored by Swinimer, has called for farming to remain small-scale “until we know more” and best seaweed farming practices have been scientifically evaluated.

It also stresses the importance of conserving natural seaweed habitats, some of which are in decline because of ocean warming.

Hesketh echoes that concern. “If you have local communities that are highly invested in both the coastal space that they’re operating in and in the industry, that may be the best recipe for sustainability,” she says.

“Because then you have people who feel accountable – not only to the community but also to the environment in which they live.”