Hidden gems - Underwater forests could help tackle the climate crisis

Kelp absorbs CO2 and has high nutritional value-but it is under threat from rising temperatures, pollution and invasive species

- Lucy Sherriff

Bubbles stream furiously behind Frank Hurd as he gently parts the curtains of giant kelp. Green and gold ribbons reach upwards through the cold waters of the Pacific Ocean towards the sun.

Hurd, a marine biologist with environmental organisation the Nature Conservancy, is diving in a kelp forest off Anacapa Island, one of the protected rocky volcanic islets that form the Channel Islands national park, an archipelago off the coast of southern California.

This thick, healthy kelp – a type of seaweed – forms a small part of underwater forests that blanket the coastline of nearly every continent. Some are relatively well-studied, including the Great African Sea Forest, a rich stretch of giant bamboo kelp spreading north from Cape Town, South Africa, to the Namibian coastline that was the setting for the film My Octopus Teacher; and the Great Southern Reef, a giant kelp forest hugging Australia’s southern coastline. But many more of these forests are unnamed and unknown – hidden underwater.

Despite being one of the fastest-growing plants on Earth, kelp has historically been hard to map because of the difficulties of measuring ocean depths with satellites. However, research published in September found that seaweed forests are more extensive than previously realised.

An international group of scientists from eight countries, led by Dr Albert Pessarrodona from the University of Western Australia, manually sifted through hundreds of studies – including local plant data records, online repositories and citizen science initiatives – to model the global distribution of ocean forests. They found that underwater forests cover between 6m and 7.2m sq km – an area comparable to the Amazon rainforest basin.