Sixty years ago, Tasmania's coastline was protected by a kelp forest so dense that it trapped local fishermen when they set out on their boats. These underwater forests, rich in giant algae tens of metres high, the "sequoias of the seas", are sanctuaries of biodiversity that are gradually disappearing due to the ravages of human activities and climate change. Yet these kelp forests, like the large terrestrial forests, are carbon traps that could help us in the climate crisis. They still need to be protected and tactfully reintroduced into the environment where they had ceased to exist. Storytelling.
Since the 1960s, Tasmania's once extensive kelp forests have declined by 90 % or more. The main culprit is climate change: these giant algae need cool, nutrient-rich currents to thrive, but regional warming in recent decades has introduced the waters of the warmer East Australian Current into the Tasmanian Seas with devastating effect, wiping out the large forests of giant algae one by one. Warming waters have also increased populations of predatory sea urchins, which gnaw at kelp roots and make the situation worse.
Tasmania isn't the only site of destruction. Globally, kelp forests are located along the coasts of all continents except Antarctica Most of them are threatened by climate change, coastal development, pollution, fishing and invasive predators. Yet these ecosystems offer considerable benefits: they protect coastlines from the effects of storm surges and rising sea levels, they clean water by absorbing excess nutrients, and they also absorb carbon dioxide, which can help reduce ocean acidity and create a healthy environment for surrounding marine life. These forests - which, in the case of the giant seaweed species that grows in Tasmania, can reach heights of up to 40 metres - also provide habitat for hundreds of marine species.
After years of studying these benefits, Cayne Layton, a researcher at the University of Tasmania's Institute of Marine and Antarctic Studies, is now trying to revive some of the struggling kelp forests. Every two or three weeks, he dives to inspect three 12-by-12-metre plots, each containing kelp shoots that grow on ropes attached to the ocean floor. These nurseries are part of Cayne Layton's project to determine whether climate-resistant "super kelps" grown in the laboratory will better adapt to the changing Tasmanian seas. But her experiment is also drawing attention to the extraordinary potential of these algae to absorb carbon and help combat climate change.
The future of kelp
One of the remarkable advantages of kelp is its ability to extract CO2 from the atmosphere. When we talk about how the oceans can sequester carbon, the conversation usually revolves around mangroves, salt marshes and seagrass beds. But," he says. the magnitude of carbon sequestered by algal forests is comparable to that of these three habitats combined".We have to be able to do that," says Carlos Duarte, a professor of marine sciences at the King Abdullah University of Science and Technology in Saudi Arabia. « Algae forests should not be ignored. They have been forgotten for far too long.".
There's a lot we don't yet understand about how algae store CO2. But researchers are beginning to get a better idea of this giant algae and how we could improve its ability to help fight climate change.
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The dilemma is that kelp itself is also under siege from warming seas - which is the focus of Cayne Layton's work. Only about 5 % of Tasmania's original forest remains. Researchers believe these plants have survived through natural variation and selection.
" It seems that some people are adapted and able to live in the modern conditions we have created in Tasmania as a result of climate change".explains the scientist.
From this remaining reserve of wild giant seaweed, he and his colleagues identified what Layton calls "super kelp" that may be more resistant to the effects of warmer seas. He collected spores, which he wrapped in strings and wrapped them around ropes rooted in the sea floor. The hope is that these super kelp spores will develop into young shoots which, in turn, will drift their own spores into ocean currents, sowing new mini-forests nearby.
" For the restoration of the giant kelp to work on a shoreline scale, we're going to have to plant a lot of these seed plots."...explains Cayne Layton. « The idea is that over time, these will spread out and eventually regroup - and there's your giant kelp forest back.".
Other kelp restoration projects around the world are addressing different threats. In Santa Monica Bay, California, conservationists are trying to save the local kelp forests from the voracious purple sea urchins, whose population has exploded since a major predator for them - the sea otter - declined dramatically several decades ago. The urchins' uncontrolled appetite has contributed to the loss of three-quarters of the bay's former kelp forest. Now, fishermen carefully hand-pick sea urchins - with a vested interest: when the kelp is restored, so is the fishery. So far they have managed to clear 21 hectares, which the kelp forest has already reclaimed. « All we had to do was get the sea urchins out."says Tom Ford, Executive Director of Bay Foundationwho's leading this effort.
The success of the project has led others to think about the carbon sequestration potential of these forests, Ford says. For example, the city of Santa Monica recently set a goal of achieving carbon neutrality by 2050, and asked The Bay Foundation how restoring the kelp could help. A non-profit association, Sustainable Surfhas also launched a program allowing the public to invest in the kelp restoration project to offset the carbon footprint.
" These kelp forests grow so fast and absorb huge amounts of carbon."says Tom Ford. In California, the focus is on preserving wilderness lands with carbon credits, he explains. But the increase in regional forest fires means that land-based forests no longer seem to be the safest option. « Now, working offshore may be a smarter option.... "
Also in the United Kingdom, the "Plan"... Help Our Kelp "The project is aimed at restoring 180 square kilometres of historic kelp forest along the south coast of Sussex. It has attracted the interest of two local councils and a water company, who are intrigued by its potential to provide a new carbon sink. « All three organizations are interested not only in carbon, but also in the broader benefits [of kelp forests]".says Sean Ashworth, Deputy Director of Fisheries and Conservation at theAssociation coastal fisheries and conservation authorities, a project partner.
Yet key questions remain as to where all the stored carbon goes. Trees stay in the same place, so we can reasonably estimate the amount of carbon stored by a terrestrial forest. Kelp, on the other hand, can float to unknown destinations, carried by ocean currents. If it decomposes, the stored carbon can be released into the atmosphere, says Jordan Hollarsmith, a marine ecologist at Simon Fraser University and Fisheries and Oceans Canada. For this carbon to be truly removed from the global carbon budget, these kelp shoots would have to be somehow rooted or transported to the high seas..
In fact, new research is beginning to paint a picture of how algae travel through the ocean. A study conducted in 2016 estimated that about 11 % of the world's macroalgae are permanently sequestered in the ocean. Most of this, about 90 %, is deposited in the deep ocean, while the remainder sinks into coastal marine sediments.
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" If the algae reach a depth of at least 1,000 metres, they are locked up and can no longer exchange with the atmosphere for long periods of time, and can be considered permanently sequestered".says Dorte Krause-Jensen, professor of marine ecology at the University of Aarhus in Denmark and author of the 2016 study. Compared to mangroves, seagrass beds and salt marshes, which deposit carbon directly and reliably in the sediments below, the variability inherent in a kelp forest makes sequestration more difficult to quantify accurately. But this could change if kelp forests were under strict human management - which is already happening with the small species of algae that are grown around the world for food and fertilizer.
Permaculture of kelp
Could we similarly bring vast kelp forests under human control for the good of the planet? Brian Von Herzen, Executive Director of the non-profit organization The Climate Foundationis of this opinion. This organization is a partner in Cayne Layton's project for climate-resistant algae, and Von Herzen is a major player in the field of " marine permaculture« The project is a type of open ocean seaweed culture that mimics wild seaweed forests to regenerate marine ecosystems, enhance food security and sequester carbon.
Von Herzen is currently testing prototype networks in the Philippines to help make algae cultivation more resilient to climate change.
At the heart of Von Herzen's vision is a network on which kelp would grow, hovering 25 metres below the ocean surface. Using solar, wind and wave energy to power their movement, pipes fixed underneath the structure would siphon colder, nutrient-rich water from the depths. This infusion of cold water would recreate an ideal microenvironment for kelp to grow; the macroalgae would then oxygenate the water and create a new habitat for fish - while capturing carbon," says Dr. Von Herzen.
While these deep-water kelp forests are only hypothetical, Von Herzen is currently testing prototype networks in the Philippines to help make algae cultivation more resilient to climate change. Algae growers have suffered significant losses due to warm ocean currents that sweep away and decimate their crops. But with the upwelling of cooler water generated by the new systems, algae are beginning to thrive again.
This project, along with others being developed off the coasts of Europe and the United States, lays the foundation for Von Herzen's ultimate ambition: to dramatically increase algae networks, eventually covering large areas of the deep ocean where they could collectively absorb billions of tons of CO2 while ensuring food security in the form of shellfish farming and fish habitat, providing what he calls "...the ultimate goal of the project...". the support of ecosystem life.".
Kelp could be rooted in the deep ocean to sequester carbon or harvested to produce low-emission biofuels and fertilizers, he says. « We are using the thriving wild kelp forest as a model ecosystem for what we can scale up in the oceans".says Brian Von Herzen.
Based on his research, Dorte Krause-Jensen is optimistic about the carbon sequestration potential of kelp and the possibility that it can be significantly expanded through sustainable agriculture. But from a practical point of view, in countries such as Australia and the United States, says Professor Duarte, "[t]hen you look at it from a practical point of view, in countries such as Australia and the United States," she says. it's harder to get a lease for a seaweed farm than it is for oil and gas exploration.". And global offset systems for carbon sequestration are not yet in place for kelp.
Christophe Jospe, director of development at Nori, a company that works to facilitate the financing of carbon reduction initiatives, says that with such a powerful sequestration tool at our disposal, we should speed up its acceptance - even though algae producers can only guarantee sequestration for about 10 years.
" We are getting into a passionate environmental debate where people are saying that it is not permanent. But nothing is permanent - and it is the carbon pool that we need to increase because of the climate crisis we are in.protests the specialist. « So, in fact, it's a huge environmental value for a program to ensure 10 years of permanence! ».
There are signs that things are gradually moving in that direction. In collaboration with Oceans 2050a global alliance for ocean restoration, led by Alexandra Cousteau, is now helping to develop a carbon credit program that could be applied to seaweed farming. This is helping to imagine a world in which we could one day invest carbon credits in kelp farms or in which restoring wild forests could count as a mitigation measure.
Meanwhile, in Tasmania, Cayne Layton continues to monitor his kelp seedling nurseries, and he urges us to be aware of what the kelp forests are already doing for us right now. « They are exactly like the forests on earth. Not many people question their value."he says. « Some people may not be interested in algae. But they may be interested in fishing, or in making sure that their seaside property is not washed away, or in making sure that their coastal waters are clean. All these things are intimately linked to the fate of kelp forests.".
Emma Bryce, journalist Ensia
Source : Ensiaas part of the Carbon Zero initiative.