Blue carbon: using our oceans to remove CO2

From kelp forests to seaweed-based 'plastic' packaging
31 August 2021

Interview with 

Sally Ashby, Sussex Kelp Project & Ayca Dundar, SoluBlue




The hot new topic in the world of carbon sequestration is blue carbon, that is using our seas and oceans to remove CO2 rather than our terrestrial ecosystems. The biggest benefit of blue carbon is that it doesn’t compete with land that could be used for farming or for building homes.

In the UK, salt marshes, kelp forests and seagrass meadows all have the potential to either rapidly draw down carbon dioxide from the atmosphere or trap carbon in muddy sediments or both. We’ve only recently begun to appreciate just how good these ecosystems can be in reducing climate change, and as a result, we’re still missing a lot of the key research to quantify blue carbon. But some estimates suggest that saltmarshes, for example, might draw down carbon as quickly as an established woodland.

We’re first going to dive into the world of seaweed and in particular, kelp. This giant seaweed forms underwater forests that have, rather like their terrestrial counterparts, been suffering from habitat destruction and now only small patches remain. But restoration teams like the Sussex Kelp project are hoping to change that, as Sally Le Page heard from project leader Sally Ashby. But what exactly is kelp?

Sally Ashby - Kelp is a term given to the large brown seaweeds or macro algae. They have a holdfast where they attach onto rocks or hard substrate, which are almost like roots, but exposed, clinging to a rock. Then they have a stem that's called a stipe, which extends up, and then they have these fronds, like leaves, that are long and can be up three metres long. So they're large seaweeds.

Sally Ashby - Kelp specifically forms habitats or aggregations like a forest, so highly dense areas. And because they're like trees in their structural form, it has this feeling of a forest. Not only is it a nursery for fisheries, it's also providing shelter and habitats for a whole raft of species that then sustain a healthy functioning ecosystem and food web.

Sally Le Page - So that's like how in a traditional forest you'll have spaces for nesting birds and small mammals. It's the same underwater?

Sally Ashby - Yeah, exactly, it's the same underwater. Ultimately we are aiming to restore a crucial marine ecosystem that supports huge amounts of biodiversity, boosts our fisheries and also protects and maintains those marine carbon stocks that are really important for climate change.

Sally Le Page - How does kelp help us with climate change in terms of carbon?

Sally Ashby - Kelp is highly productive, which means it draws down huge amounts of carbon dioxide from the atmosphere, much like trees and plants do. The difference with kelp is that it doesn't then sequester that carbon into the soil or sediment directly. It takes that carbon and then feeds the secondary production, so the fish that we eat and all the other animals. We think that approximately only 10% of kelp carbon would be permanently sequestered and almost 90% then goes into feeding coastal ecosystems.

Sally Le Page - And what is the state of kelp forests in the UK?

Sally Ashby - The kelp in the south of the UK has experienced serious decline. In Sussex, historically, there were these vast kelp forests in the eighties, but we've lost almost 96% of those kelp forests.

Sally Le Page - And what is that in terms of absolute area? If we've lost 96% and we're down to 4%? What is that in terms of square kilometres?

Sally Ashby - It used to be that the historic kelp bed was about 170 square kilometres. So it's a huge area.

Sally Le Page - And that's just Sussex.

Sally Ashby - And that's just Sussex, but ultimately, globally, kelp is an ecosystem that is in decline and highly threatened by a variety of anthropogenic factors.

Sally Le Page - What is causing the decline in kelp?

Sally Ashby - The impacts on kelp are complex and varied, but pollution, eutrophication, impacts of fishing - there's a whole variety of factors.

Sally Le Page - As part of the Sussex Kelp Project, you are in charge of the restoration. So how do you restore a kelp forest?

Sally Ashby - Specifically in Sussex, what we would hope for is that the kelp is naturally restored. There's 300 square kilometres where bottom towed trawling has been banned, which means the seabed has a chance to recover.

Sally Le Page - What is this kind of trawling? What is it used for?

Sally Ashby - Bottom towed trawling is used to fish for sole and plaice that inhabit the seabed. So it is a very destructive practice for the seabed because ultimately you're towing very heavy gear and picking up everything and anything in its path.

Sally Le Page - And obviously people aren't trawling for the sake of trawling, they're trawling because fishing is their livelihood and it's what allows them to make a living. So will this project just stop the local fishing industry from surviving?

Sally Ashby - No, not at all. We're working closely in this project with the local fishing community. The Nearshore Trawling Byelaw was brought in specifically by the Sussex Inshore Fisheries and Conservation Authority who managed the fisheries. The point of the byelaw is to restore the kelp, to restore the ecology and the ecosystem, so that it supports a really booming fishing industry.

Although this particular project is aiming to restore a natural ecosystem with all of its biodiversity benefits, material scientists have also been looking at seaweed's remarkable ability to photosynthesise and trap carbon. And they're trying to put it to use, to solve some of our other global crises. One such entrepreneur is Ayça Dündar, who was frustrated by the climate crisis and also our plastic waste problem. Her solution was to invent a fully compostable alternative to plastic film made instead from sustainably farmed seaweed. Along with her husband Francis Field, they cofounded the startup company, Solublue. Sally Le Page went to visit them both in Cambridge to find out more about this material that they claim can help trap carbon from the atmosphere, prevent food waste and reduce plastic pollution - all from seaweed.

Ayça - Seaweed is a great material that doesn't need land use. It doesn't need fresh water to grow, unlike trees. It captures a lot of carbon - more than trees - and grows really fast. So it's a great material and resource.

Sally - How do you go about turning seaweed into packaging?

Ayça - The main process is seaweed is harvested and, most of the time, it is dried and it goes through a cleaning process. You blend the seaweed with water if it is dry, so you hydrate it and then you cook it. That's the bit that we engineered.

Sally - And in front of us, we have a whole table of goodies here. Can you talk me through what we're looking at?

Ayça - We have samples of some of the structural containers we made as well as film samples. And what we did was several tests of putting fresh food in our packaging. As you can see with this cheese sample, the one that we packed in our packaging is still preserved after two years in unrefrigerated conditions, whereas the same cheese sample packed in plastic got mouldy after three weeks' time in unrefrigerated conditions.

Sally - You say cheese - what I'm looking at is a black and white splurgy, mouldy mess. I'm going to have to take your word that this is cheese, or was cheese, because it's certainly not cheese now. So this is the standard clear plastic film that cheese normally gets wrapped in. Now I've picked up the Solublue sample - your seaweed alternative sample. In terms of the plastic film, it feels the same. I would never have guessed that it's made of seaweed. It's completely transparent, it's very thin, it's very flexible. But it looks like cheese. I mean, it looks like hard cheese.

Ayça - We have tried it and it tastes a little bit like mature cheddar.

Sally - Do you agree with that?

Francis - Yes. I thought it was closer to Parmesan, but it was edible. The discovery that we could actually extend shelf life and reduce food waste was a real breakthrough for us, because today 40% of food produced is never even eaten. We need to tackle that urgently and one way to do that is with our packaging. The seaweed that the farmers are growing is capturing a lot of carbon and it's doing that more effectively and faster than trees are doing it. When we take that seaweed and we make it into our packaging, that carbon remains captured. And as part of the way our product works in use, we're capturing food waste as well. All of that can be placed in the same composting bin - we're simplifying waste streams - and that carbon is captured, retained. And when composted, biomass is getting locked back into the soil.

Sally Le Page - Talk me through it as an example, because right now at the bottom of my fridge I have got a cucumber half wrapped in plastic and it's gone really soggy and mushy and kind of disgusting. What is the alternative if we were to make that packaging out of seaweed, instead of out of plastic?

Ayça - What we have observed is that after three weeks there was no sogginess. There is no mould forming because the seaweed material that we have developed is hydrophilic - it absorbs excess moisture from food. It is not a good environment for bacteria to grow.

Francis - So your cucumber doesn't go to waste and you don't need to cut the packet off it. You don't need to feel guilty about throwing it in the bin because you're putting it to compost.

Ayça - It will be very good for big retailers that right now had to throw away tons of spoiled cucumber to landfill. It can be used as an animal feed or can be composted.

Sally - You said your packaging is edible - edible by humans?

Ayça - Yes, it is edible by humans. And also animals.

Sally - Can I try some?

Ayça - Of course, you can try it.

Sally - Do you have scissors so I can snip off a little quarter?

Sally - Okay, this feels really weird. It's literally just looks like plastic. This is definitely the seaweed one and not the non-seaweed one I'm putting in my mouth, right? Wow, it really absorbs the moisture. It's stuck to the roof of my mouth. It's like eating rice paper. I mean, I've never really eaten plastic so I can't really tell you how it differs from eating plastic.

Sally - I can tell that I can bite through it. It's not just a solid sheet. It's now slightly turning into like a dried out fruit leather almost. It doesn't taste of anything at all, but there we go. And if I haven't died by the time the show is broadcast, we can say that it is edible by humans.

Francis - We don't encourage people to eat it, but you can if you want. And it means that if an animal eats it, it's not going to clog their digestive system or something like that.


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