Words by Maddy Simmonds
Images by Sarah Jane Humphrey
For some people, seaweed is the smelly, slimy thing that gets inconveniently tangled in their feet at the beach, for others it’s a beautiful glinting gem in the sand from which they take inspiration, but in reality it is much more than either of these things. Recently there has been a lot of buzz about the role of seagrass in the planet’s health, but its “cousin” seaweed also has environmental superpowers.
Seaweed is easy to grow and is very versatile in its uses, from being used in medicines to beauty products, but it also has an important role to play in combating climate change. Seaweed is a macroalgae and, like plants on land, it photosynthesises meaning it takes in carbon dioxide and produces oxygen. This oxygen production is important in ensuring there is enough oxygen available underwater to sustain life. Declining oxygen levels can have serious consequences such as reduced biodiversity and changes in distributions of species.
Seaweed is also very efficient at storing the carbon dioxide it absorbs – coastal marine systems can absorb carbon at rates up to 50 times greater than forests on land. In fact, seaweeds are thought to absorb 200 million tonnes of carbon dioxide every year globally, which is equivalent to the annual emissions produced by the state of New York State. Trapping carbon dioxide under the water like this is known as “Blue Carbon”.
As part of their carbon absorption ability, seaweed also helps to counteract ocean acidification. When carbon dioxide levels increase in the atmosphere, much of the gas dissolves into the ocean which reduces the water pH and has damaging consequences to the underwater ecosystems. But as the seaweed takes in carbon dioxide for photosynthesis, it helps to raise the pH level again. This has positive knock-on effects for creatures who live in seaweed habitats, like crustaceans and molluscs, whose shells can weaken at lower pHs.
Seaweed can also help mitigate climate change in a more unexpected way – by reducing the methane burps produced by cows! Methane is a much more potent greenhouse gas – it has a global warming potential of about 28 times more than carbon dioxide. And when you realise that each cow can burp between 200-500 litres of methane every day that’s a whole lot more warming going on! But adding seaweed to cattle’s diet can reduce the methane produced thanks to the strong antioxidants and tannins it contains.
Using seaweed as a supplement for cows, and other farm animals like chickens and pigs, also means that less land would be needed to grow feed crops for them which could help reduce deforestation.
Seaweed can also be harvested to be used as a more sustainable food source for the growing human population, as it doesn’t need fertiliser, pesticides, freshwater or land. Its rapid growth means that it can be ready to harvest in six weeks, and it has good nutritional value, providing minerals, iodine and amino acids – one hectare of seaweed can produce more protein than the same sized cattle farm! It’s estimated that if seaweed harvest can be increased to 14% a year by 2050, it could increase the world food supply by 10%.
Seaweed could also help contribute to solving our plastic pollution crisis. Over 300 million tons of plastic is produced each year and over half of this is single-use plastic, much of which ends up in the ocean. Food packaging in particular is behind over a third of the ocean’s plastic problem. Unsurprisingly, the plastic problem has worsened since the pandemic. But seaweed can be processed to form a plastic-like substance which can then be used for things like tea/coffee sachets, wrappers for fast-food, cups and other food containers. These bio-plastics are natural and biodegradable – they can break-down in 4-6 weeks compared to the several hundred years it would take traditional plastic to degrade. The idea of using seaweed in this way is not just being developed in the UK but also places like Indonesia, which is vital as plastic waste isn’t just one country’s problem, we all contribute to this form of pollution and so we must work together to solve it.
Seaweed clearly has huge potential as a solution to many of the problems faced globally, but to really make a difference seaweed farming needs to be scaled up and farmed in open ocean where the size of seaweed production isn’t limited by space. The technology to do this isn’t quite there yet but investments are being made in order to build and test equipment that can survive the harsh open-ocean conditions. There also needs to be a balance between all the different uses of seaweed – we should be harvesting a sustainable amount so that it can feed humans/animals or be used as a bioplastic but also leaving enough where it is in order to act as a carbon sink. Finally, seaweed is only part of the solution. We still need to reduce carbon emissions in other ways, especially as seaweed itself is still vulnerable climate change – let’s try not to kill it off before its full potential has been realised!
“Oh! Calls us not weeds, but flowers of the sea,
For lovely, and gay, and bright tinted are we!
Our blush is as deep as the role of thy bowers –
Then call us not weeds, we are ocean’s gay flowers.”
(By Mary. M Howard in Ocean Flowers and Their Teachings, 1846)