Aquaculture Biology

Farmed Kelp to the Rescue? Not So Fast, Say Researchers

Kelp farming is on the rise across Europe and North America, and all the headlines say that’s a good thing for fighting climate change. But scientists say we need to make sure kelp farms don’t spawn even more environmental problems. 


Grebe, Gretchen S., Carrie J. Byron, Adam St. Gelais, Dawn M. Kotowicz, and Tollef K. Olson. “An ecosystem approach to kelp aquaculture in the Americas and Europe.” Aquaculture Reports, vol. 15, 13 September 2019,


Kelp farming has existed in the U.S. for just nine years. As the industry gains traction, scientists and farmers want to make sure it stays sustainable. Image by bluebudgie from Pixabay.

Google ‘kelp farming’, and you’ll find headlines claiming that the practice will help solve everything from climate change to poor nutrition to food insecurity. Kelp stores carbon; kelp can soak up excess fertilizer running into the ocean from agriculture on land; kelp can replace chemical fertilizers; kelp doesn’t require converting an inch of rainforest or other habitat to farmland. Kelp simply means any large algae in the ocean, and the headlines about farming microalgae, kelp’s smaller cousin, also include big promises about algae-powered biofuel and algae-based alternatives to plastic. All of these headlines are true and exciting. In the last decade, the practice of farming kelp and other algae has shot up from nearly nonexistent in Europe and North America to being one of the hottest topics in sustainability. But there’s more to the story of kelp farming. A new study takes a closer look at the booming industry, and how it can develop sustainably in the global West. 


Kelp Farming 101

Farming kelp isn’t a trendy new idea: the practice has flourished in Korea and Japan for half a millenium. China, Korea, and Japan are still the global hubs for mass producing seaweed as a commodity, with dozens of species of edible seaweeds and seaweed products on the market sourced from wild kelp beds as well as farms. Kelp farming is considered aquaculture, or water-based farming, but growing kelp is more like tending a rather sedentary, self-sufficient flock of sheep than managing a crop.Kelp doesn’t need any fertilizer, tilling, or watering. It photosynthesizes just like plants do, but unlike plants, kelp absorbs nutrients directly from the water along its whole body as it sways with the waves.

From Grebe et al.: a typical northeast kelp farm setup


To start a kelp farm, the ‘farmer’ collects some fronds from wild kelp and brings them into an aquarium. In the tank, the kelp’s reproductive tissue releases billions of microscopic spores into the water. These are called gametophytes, and they are an alga’s first life stage. The tiny gametophytes need to settle on a surface, and the farmer normally encourages the young drifters to attach to a longline rope.

After settling on the rope, the gametophytes mature and reproduce sexually. ‘Male’ gametophytes release sperm, which fertilizes the ‘female’ and creates the second life phase: the sporophyte. The sporophytes are still microscopic, but they quickly grow into the mighty, filamentous algae that we call kelp. 

Kelp aquaculture in the Netherlands

Once the sporophytes are anchored along the longline rope, the rope is placed in the ocean close to shore where the kelp can continue to thrive and grow on their own for several months. Some species can grow over a foot per day in good conditions, handily beating the world’s fastest growing land plant (giant bamboo). Because of how low-maintenance the ‘crop’ is, kelp farming actually has one of the lowest barriers for entrepreneurs entering the aquaculture business — in Maine, $1,000 is enough for a kelp-farmer to purchase all the startup equipment.

So what’s the issue?

While it’s true that kelp farming is an ultra-sustainable kind of aquaculture, scientists warn that keeping it that way as the industry expands might take some work. Researchers hope that once policymakers and business owners know more about the possible side effects of mass kelp farming, they can all work together to prevent them.

Genetic diversity is the biggest of these effects. Every gametophyte in the tank stage is genetically identical to its ‘parent’ kelp from the wild, and since each parent releases billions of spores, farmers often don’t collect many different parents and end up with a tank full of clones. The sexual reproduction stage helps mix up the genes, but all the kelp that leaves the aquariums is still about as closely related as siblings or cousins. And much like thousands of close human family members coexisting in the same space, that can cause problems, not just for the farmed kelp but also for wild kelp forests nearby that will receive billions of very similar spores when the farmed kelp starts the reproductive cycle over again. It’s as if a single family made up half the population of a town – except the kelp can’t move away. 

Having similar genes puts a population at risk for diseases. It also limits how the population can respond to other stresses, like climate change. Diversity keeps populations healthy, and for kelp especially, the opposite is also true: it’s hard to stop a lack of diversity from affecting an entire population, including kelp living far from the farm, since the billions of spores drift freely through the water.


A researcher grabs fistfuls of sugar kelp (Saccharina latissima), one of the most common commercial species farmed off the U.S.’s northeast coast.

The longline ropes the farms use to grow the kelp on may be another cause for concern. Marine life entanglement is already a global problem, and on the east coast of North America, kelp farms overlap with critical habitat for the endangered North Atlantic right whale. Researchers are still searching for a solution to prevent kelp farm expansion from trapping whales and other large marine life in a kelpy web of rope.

Other potential problems with large-scale kelp farming could actually be turned into advantages. Kelp sucks up a lot of nutrients to fuel its speedy growth, and researchers wonder whether large artificial kelp farms could hog all the nutrients in an area of the ocean. With some smart planning, this could be a huge benefit of kelp farms instead of a drawback, because many coastal ocean areas downstream from agriculture suffer from too many nutrients. This nutrient overload from fertilizer runoff causes ‘dead zones’, massive oxygenless, largely lifeless patches in the ocean. Huge kelp farms placed in areas suffering from dead zones could actually help reverse the problem by soaking up some of the nutrients, and releasing more oxygen into the water.

The future of kelp farms

Like any up-and-coming industry, large-scale kelp farming in North America and Europe will suffer some growing pains. Kelp farms are good for so many parts of society–from the climate to local economies to nutrition–and it makes sense for just about everyone to help get more kelp on the market. The good news is that the consumers of North American and European kelp care about their product’s sustainability, and are willing to pay more for it. This is partly why sales from European and North American kelp farms make up 4% of kelp’s global production value, even though these farms are just a tiny portion of the global market. 

The biggest risk right now with kelp farming is perhaps not an ecological issue, but a human communication issue: if we squander the chance to plan ahead for serious pitfalls and problems, we’ll stumble over a rare chance to develop a long-lasting industry that could actually help the ocean instead of degrading it. But if scientists, regulators, and farmers all link up instead, large-scale kelp farming in the U.S., Canada, and Europe will grow into a truly sustainable and unstoppable business model.

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