Underwater forests for preserving climate and biodiversity

by | Aug 31, 2023


We’re very pleased to be able to share with you an exciting excerpt from Vincent Doumeizel’s new book ‘The Seaweed Revolution’.  It explores how seaweed has shaped our past and can save our future. It’s a fascinating read and has reinforced, for us here, the importance and benefits of the seaweed in our seas.

We’ve chosen to share this first excerpt ‘Underwater forests for preserving climate and biodiversity’ as it’s hopeful and informative, just like the rest of Vincent’s book.




‘First of all, our immediate concern is clearly preserving life on earth.

Today, 50% of the carbon on our planet is stored in ocean sediments. The oceans appear to have far greater potential to combat global warming than forests and other terrestrial ecosystems.

The biomass of seaweed in the ocean is greater than that of all the forests on land. The amount of carbon dioxide captured by wild seaweed worldwide is almost equivalent to the amount of gas emitted by France and the UK combined.59 But these carbon retention capacities are under threat. The largest types of seaweed have the greatest potential for carbon sequestration. Unlike many plants, long brown seaweed does not thrive in heat or warmth, but in the cold. It grows in southern Chile, Canada, New Zealand and Norway. Wherever it finds cold water.

Unfortunately, this water is not as cold as it used to be, and is still getting warmer… Global warming means that many of these larger types of seaweed risk being replaced by other smaller ones, or even not being replaced at all. This would lead to the disappearance of the entire surrounding biotope, and the cycle of climate change could be further accelerated.

In California, the Kelp Highway has almost disappeared over the past decade. One of the world’s largest wild seaweed forests, the Amazon of the oceans, home to a rich ecosystem spanning tens of thousands of kilometres, has lost 90% of its surface area in less than five years. As if it’s been wiped off the map.

As early as 1845, Charles Darwin noted that ‘The number of living creatures of all Orders whose existence is intimately dependent on kelp is wonderful. I can only compare these great aquatic forests… with terrestrial ones in the intertropical regions. Yet, if in any other country a forest was destroyed, I do not believe so many species of animals would perish as would here, from the destruction of kelp.’60 In the American West, 750 species face extinction because they depended directly on these ‘miraculous’ kelp forests that absorb so much carbon from the atmosphere and protect the coasts from rapid erosion.61 This worrying disappearance of seaweed is not directly caused by water warming, but is the consequence of the disturbance of ecosystems as a result.

In California, but also in Norway or Japan where the trend is unfortunately the same, the culprits behind this massive deforestation are innocent little red sea urchins. Their destructive proliferation is a consequence of the disappearance of their predators, the sunflower sea star. 

Previously abundant, they were eradicated by diseases during the intense warming of the Pacific and the two years of extreme drought on the American West Coast, which ended in 2015.

Rarely has such a drastic decline in a species been observed. In the absence of the sunflower sea stars, the sea urchins proliferated and, as they grazed on seaweed, they devoured practically all of it. In doing so, they destroyed a habitat that provided food and shelter for juvenile fish, octopus, sharks, crabs, shellfish, birds, herons, otters and even sea lions. Without plants, on land and at sea, there will be nothing left.

Today, California has several thousand kilometres of what some call ‘the lost desert of sea urchins’. Ironically, these sea urchins are not even marketable because there are too many of them and they don’t eat enough to reach a sufficient size.

Sea urchins are unique animals: they can sometimes live for up to 200 years; their vital and reproductive functions do not age; and they are able to modify their feeding behaviour to overcome crises. When resources are scarce, they have the ability to lie dormant for many years, remaining puny and subsisting on any waste matter in sight.

Tasmania used to have huge reserves of giant seaweed, but in similar circumstances caused by global warming and the overfishing of lobsters – which are also fond of sea urchins – it has now lost almost 97% of its Macrocystis.

Sometimes climate change is not the only culprit. Trawling and dredging of the seabed can quickly wipe out a kelp forest. Greenpeace therefore decided to install 180 blocks of granite off the coast of Sweden in order to protect certain species of seaweed by preventing these machines from accessing ‘marine protected areas’ (MPA) where fishing rules were too rarely respected. The destruction of ocean ecosystems is a survival issue for all of us, one that goes far beyond climate change.

Yet, although we are rightly alarmed by a fire on land in the Amazon or Australia, it is rare to see front-page news stories covering the disappearance of aquatic forests, which are the second lung of our planet; because we know so little about these forests and we see hardly any images of them. But the forests are also burning under the sea. Far below the waves, life gradually disappears to give way to a liquid desert of sand and rock, where nothing grows and wildlife is disappearing.

The situation is not hopeless, however, and it is certainly not time to give up. Seaweed has been able to withstand many changes over these billions of years.

Somewhat paradoxically, the predicted melting of the sea ice could lead to a cooling of the oceans, giving hope for a return to more favourable water temperatures and also freeing up space for the development of our underwater forests.

Thus, the types of seaweed disappearing from certain geographical locations will be replaced by others and will be able to develop in new zones closer to the poles, where the conditions are more favourable for them.

And even in areas where kelp forests are disappearing, there are solutions. The great advantage of seaweed is the speed with which it can grow. When a terrestrial forest disappears, trees can be replanted, but it will take years or even decades for it to return to its original state. In the case of a kelp forest, three months can be enough to re-establish the existing vegetation and allow life in all its forms to flourish again.

There are many examples. In the 1970s, Norway lost 8,400 square kilometres of its Laminaria hyperborea forests due to an explosion in sea urchin populations. Climate change plus the development of predatory crabs have enabled 3,400 square kilometres to be restored in just a few years. The socalled ‘green gravel’ method of seeding gravel and dropping it into the sea has proven to be very effective. However, the 15,000 kilometres of coastline north of Troms still suffer from the proliferation of sea urchins. Up to thirty sea urchins can be counted per square metre, when the normal concentration is two. We still need to find intelligent ways of dealing with the problem of sea urchins.

Urchinomics, a young Norwegian company working in California and Japan, is making great strides in this area. Their idea is simple: based on the principle that a well-fed sea urchin is an expensive delicacy in Japan and in a growing number of other countries, the company’s idea is to take sea urchins from the ocean and feed them with seaweed waste in landbased ponds. The company has developed a very specific aquaculture methodology for feeding them and making them grow quickly. Once the sea urchins are fully grown, they are sold at a premium, which pays for the divers to go and collect more. The start-up is therefore transforming a pest into a delicacy. It has even gone a step further, because with sea urchins, only the ‘gonads’ (the inner part) is edible. Urchinomics has therefore managed to find a way to grind up the spines and use them as a very effective fertilizer to accelerate the growth of kelp.

This methodology has yet to be refined and large-scale pilot projects have yet to be developed. But these experiments prove that it is possible to help ‘repair’ anthropogenic damage quickly. Above all, it shows that it is possible for largely degraded marine ecosystems to regain their equilibrium, but that a human touch, carried out with great scientific rigour, is often necessary to enable this reversal.

In the light of these recent experiences, the idea that ‘leaving the oceans alone’ is the best way to restore their lost vitality is proving to be a dangerous gamble. The impact of humans on the oceans is already too great to leave the latter to fend for themselves… We still need to work out how to support our oceans in order to live in harmony with them. We urgently need an approach aimed at protecting, restoring and maintaining these forests, to enable them to carry on impacting our climate.’


Huge thanks to Vincent Doumeizel for sharing this essay from The Seaweed Revolution published by Hero Press. You can buy the book here or pick up a copy in our shop at Halen Môn. Translated by Charlotte Coombe, cmctranslations.com.

Your basket