Can underwater forests help us fight climate change?

This is one of the luxurious landscapes that inspired James Cameron for one of the scenes in his film. Avatar 2 – Waterway : this underwater forest of brown algae or “laminariales” (genus) is easily recognizable by its green and gold ribbons stretching across the glistening surface. Laminaria, Macrocystitis and Nereocystis – also called “kelp”).

The most famous kelp forest is located off the coast of Namibia and South Africa – and was notably used as a scene for an Oscar-winning documentary. The wisdom of the octopus (2020), all continents (except Antarctica) are actually covered by more or less extensive underwater forests, some of which still remain unknown.

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6 million km2 of underwater forests

According to a recent study published in the journal Advances in science (9/2022) and relayed watchmanespecially based on analysis of data from participatory science programs.

By carrying out photosynthesis, brown algae capture water-dissolved CO2 – the main greenhouse gas released by human activity – to grow. Some of their organic matter sinks to the bottom of the ocean after the death of either the algae or the organisms that feed on them.

But unlike underwater meadows, or “seagrasses,” composed of aquatic plants rooted in sediment, algae float and therefore cannot store carbon directly in the soil. In addition, we must consider the carbon balance of the organisms living in these underwater forests, which, like us, release carbon dioxide by breathing (Conversation).

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In addition, warming water could reduce the carbon storage capacity of underwater forests, accelerate the decomposition of algae, and ultimately reduce the proportion of organic matter growing on the ocean floor, according to another study (PLOS Biology8/2022).

If their climate assessment is certainly contradictory, on the other hand, the importance of these underwater forests for biodiversity is undeniable. Thus, they provide food and shelter to a variety of fish, such as the common sea dragon.Phyllopteryx taeniolatus), a cousin of the seahorse endemic to Australia’s whale forest and many other marine animals such as the sea otter and gray whale in California.

Most of the world’s kelp forests are not even mapped

Unfortunately, underwater forests face a triple threat: global warming, pollution, and rising sea levels with invasive species. For example, the number of cabbage eaten by the sea urchin off the coast of California has declined by more than 95% in recent years – its population has exploded in the absence of its predator, the starfish, and even been decimated by a deadly disease. to the warming of the waters.

According to a study conducted in New Zealand and published a few days ago, warming water can have a direct effect on the giant algae that make up underwater forests, especially by reducing the germination of reproductive spores.PLoS One12/2022).

What about the lesser-known underwater forests of California or Oceania? It’s hard to say yet. “Most of the world’s pumpkin forests are not even mapped, let alone monitored“, explains Dr. Karen Filbee-Dexter, a marine ecologist and co-author of the published study. Advances in sciencequotes watchman. According to him, this lack of research is associated with the more difficult diving conditions in the cold and hard waters where these forests grow, compared to the calm and pleasant warmth of, for example, coral reefs.

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Researchers nevertheless hope to increase their knowledge of these fragile yet vital marine ecosystems in order to improve their conservation. New technologies like drones, satellites and even artificial intelligence (AI) can help them.

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