3, 2, 1… let’s go!” shouts João Franco while rolling backwards from the boat and entering the water. The water temperature is 14 degrees Celsius and the visibility is poor – something that concerns Franco’s dive partner, Álvaro Sánchez. “I hope we can see something down there,” he says before the pair start their descent. The duo dives down to 20m and starts exploring the luxuriant kelp forest. The environment is shady, largely due to the poor visibility, but marine life is rich and abundant. Small fish of different species abound in this habitat. Large sponges of different colours and shapes cling to the few rocks that are not covered by algae. 

A few minutes later, one of the divers identifies the presence of sori (reproductive structures that contain and produce kelp spores) in one of the kelp blades. He cuts the section with a knife and places it in a container along with sea water. Hand signals are exchanged to end the dive and the team ascends to the surface. The dive represents the first phase in a process being developed that could help restore abundant kelp forests to the ocean.  

Innovative solutions will play an important role in counteracting the ever-intensifying trend of habitat loss and destruction that the ocean is currently facing. One of the more effective land-based solutions being used to counteract deforestation is based on replanting trees. This restoration process recovers lost habitats and their associated biodiversity, and increases the absorption of greenhouse gases. The equivalent of terrestrial forests in the ocean are kelp forests. Kelp is the general name given to a group of brown algae species, some of which can grow to more than 60m tall. Kelp forests are found along 25% of the world’s coastlines, generally in cold and nutrient rich water, in temperate and polar regions. These marine forests play a critical role in balancing the health of the ocean and the planet. They provide food and shelter for many marine species, create complex habitats, and are considered hotspots of biodiversity. According to some studies, kelp and other types of marine vegetation absorb up to 20 times more carbon dioxide per acre than terrestrial forests. But they also reduce the ocean’s acidity, counteracting the worrying trend of acidification that is affecting species, habitats, and ecosystems. In short, these forests are an important weapon in the battle against climate change.

Despite this, the degradation and loss of these submerged forests is happening at an alarming rate. It is estimated that half of the world’s kelp forests have been in decline in coastal areas for 50 years. Pollution, overexploitation, coastal development, marine heatwaves, and ocean warming are some of the factors causing the degradation. To counteract the loss of terrestrial forests, several reforestation initiatives have emerged worldwide, some of them having produced promising results. The question then arises: can we reforest underwater habitats too? The difficulties inherent to working underwater, the costs involved, and the complexity of the species’ biology make ocean replanting significantly more challenging than the equivalent process on land. Considering these challenges, any prospective replanting process needs to be scalable, easy to deploy, and relatively low-cost. This ‘accessibility’ of deployment is ultimately what will enable meaningful restoration, and even the creation of new forests in locations with favourable conditions. 

Of the many global initiatives working to overcome these challenges, the ‘Green Gravel’ technique being developed by Portugal-based Seaforester is particularly interesting. Developed by scientists in Norway and Australia, the Green Gravel methodology is simple: kelp spores are attached to small stones in a laboratory, where they germinate under controlled conditions. After that, the stones are dropped into the sea and, if the conditions are favourable, the small kelp plant that has attached itself to the stone will grow and further attach itself to the substrate, potentially contributing to a healthier kelp forest – or giving rise to a new kelp forest entirely. 

Seaforester is part of the Green Gravel Action Group, a network of research centres working on the development of this special methodology. In the long-term, they think the process could play an important role in global kelp forest restoration given the limited barriers for people and organisations wanting to contribute to this mission. Thomas Wernberg, one of Seaforester’s founders, a professor at the University of Western Australia and Researcher at the Institute of Marine Research in Norway, describes ‘Green Gravel’ as “a technique that should be adaptable for use with a variety of kelp species and deployable by community groups, institutions and conservation organisations alike”.