The Need for Seaweed

Why seaweed aquaculture is the solution to copious environmental, health, and socioeconomic problems caused by ocean acidification and greater climate change.


Burdened by the responsibilities accompanying the predicament of having been born on a dying planet, I am relentlessly in search of climate change solutions that are convincing enough with regards to efficacy for me to devote all of my life's energy toward. Too often I am left disheartened by so-called solutions I find far fetched, unrealistic, slow acting, or incapable of providing environmental justice in tandem with the intended counter-climate change action. However, recently one solution has resonated with me and has provided me with a fresh sense of hope and direction. That solution is seaweed.

The Need

As anthropogenic, or human caused, carbon dioxide admissions accumulate in the atmosphere, carbon enters the ocean at the surface where the air meets the sea. Here, a chemical reaction between carbon dioxide and water form carbonic acid. By virtue of this reaction, carbon emissions have caused a 30% rise in surface water acidity compared to pre-industrial levels. By the end of the century surface waters are expected to reach levels 50% more acidic than before the industrial revolution.

Unsurprisingly, ocean acidification has dire impacts on marine ecosystems. When carbonic acid in water ionizes, or separates, it forms hydrogen ions and bicarbonate. Bicarbonate consists of a carbonate ion with a hydrogen. The carbonate ion is vital to the creation of shells and skeletons of many species of marine life. However, the hydrogen ions formed during the ionization of carbonic acid react with free carbonate ions in the sea to form additional bicarbonate. This causes a shortage of carbonate ions that makes the formation of shells, made of calcium carbonate, significantly more challenging for species like clams, oysters, mussels, starfish, some plankton, and coral. The reduced productivity of these species is problematic because their success is vital to marine ecosystems. For example, pteropods, a type of plankton, are an important basis for the marine food web but near the shore, in more acidic waters, they are found to have 37% less thick shells.

However not only species dependent and calcium carbonate are impacted directly by ocean acidification. Fish have to exert more energy in increasingly acidic waters in order to stabilize their pH. Higher acid levels in water can also induce behavior changes, including an inability for clownfish to recognize the presence of predators. Scientists suspect that some behavioral changes within fish in acidic waters are due to an interruption the acidic water causes in fish ability to interpret a neurotransmitter known as GABA.

The reduced productivity of such marine species has impacts beyond the sea. As it stands, fish is a major source of protein globally. In some places, greater than 50% of dietary protein is consumed via fish. Communities dependent on fish for food are often correlated with nations that are considered the most vulnerable to the effects of ocean acidification and climate change. Therefore, the depletion of marine ecosystems via ocean acidification and climate change will be detrimental to human health by exacerbating pre-existing nutritional insufficiencies especially in marginalized coastal communities around the globe. Furthermore, 300 million people are employed within the fishing industry, mostly in small-scale fisheries. The loss of marine species will result in the loss of jobs dependent on marine ecosystems and will leave a gap in coastal diets.

The Seaweed

Although seaweed, which includes kelp, is an algae and not a plant, like all photosynthesizing species it needs carbon dioxide to grow. Much like how planting trees is regarded as the natural thing to do in order to ‘help the environment’ on the land, growing seaweed should be seen as the analogous solution in the sea.

Growing seaweeds like kelp, also known as seaweed aquaculture, potentially reduces the acidity of the water, or raises the pH, where it grows. In a 2020 study, measurements taken in Monterey bay revealed that kelp’s use of the surrounding CO2 meant the pH near the surface of the water within the kelp forest had a higher pH than outside the kelp. This indicates that the kelp reduces the acidity of the water around it which would mean a kelp farm would provide improved conditions and habitat for species sensitive to pH changes such as the aforementioned shellfish.

In addition to providing a local refuge from the stressors of ocean acidification, kelp forests can function as a barrier against storms, a protection which will become progressively more valuable as climate change gives rise to increasingly extreme weather. In an Australian study from 2019 it was found that waves in kelp beds were less intense, or attenuated. Although the extent of kelp’s potential efficacy as a natural infrastructure requires further research, seaweed aquaculture could potentially serve as a form of protection for the multitude of coastal cities globally at the mercy of intensifying climate change driven storms.

Another benefit of growing seaweed is that the growth of the algae makes use of pollutants from land based agriculture like nitrogen that runoff into the ocean. In the ocean nitrogen pollution creates dead zones. However, seaweed absorbs the nitrogen and therefore seaweed farming could alleviate the stress of nitrogen pollution on ecosystems in coastal waters. Seaweed also takes up phosphorus sources from land based agriculture fertilizers in the ocean and can be used to produce kelp based fertilizers for land agriculture that effectively recycles the phosphorus. This is an appealing alternative to the expensive fertilizers sourced from exhausted phosphorus reserves.

With an average protein content of 19% and because it contains the same omega-3 oils that make fish nutritiously desirable, seaweed has a plethora of nutritional benefits. In fact seaweeds contain compounds protecting against parasitic worms or anthelmintics, as well as antibacterials, antifungals, antioxidants, antivirals, anti-inflammatories including those used to treat the bites of poisonous snakes, antidiabetics, antihypertensives and hepatoprotectors. For coastal communities, where the loss of fish stocks will leave a detrimental nutritional vacancy, seaweed could function as a plausible dietary replacement or supplement.

Beyond feeding people, seaweed can also serve as a food source for livestock in such a way that allows them to be a more environmentally viable source of protein. In a study conducted by researchers at UC Davis, it was found that by including red seaweed in the diets of steer their methane production decreased by over 80%. Methane is a greenhouse gas that exceeds CO2 in its ability to capture the sun's heat and therefore whose production, including by virtue of the digestive processes of livestock, greatly contributes to the warming of our planet.

Currently the seaweed aquaculture industry is primarily dominated by China but it can be found in coastal regions globally. Operations range in size from large industrial operations to smaller “labor-intensive” ones in places like Tanzania. In the February 18, 2021 episode of the podcast “How to Save a Planet” by Ayana Elizabeth Johnson and Alex Blumberg, the pair interview Bren Smith, the co-founder of Greenwave, an organization dedicated to promoting a kelp-based regenerative ocean faring model, and the owner of his own sugar kelp farm. Smith envisions a world in which seaweed uses and products are as ubiquitous as soy’s. However, he says that the challenge will be creating a domestic market for seaweed.

From where I sit, bright eyed and eager to see changes in how we reckon with and address climate change, the need for seaweed is undeniable. With the myriad of options for seaweed's use following cultivation enumerated above, in addition to the promising but less certain uses of seaweed as biofuel and bioplastic, I have no doubt that kelp farming and seaweed aquaculture can form a market domestically, it's just a matter of planting the seed.