Forests of golden kelp, a type of brown seaweed that grows in cooler waters, weave along the coastline of southern Australia. But many people aren’t even aware that it’s there, says Adriana Vergés.

“I live in Sydney — it’s Australia’s largest city — and it has absolutely gorgeous kelp forests,” Vergés, a professor of marine ecology at the University of New South Wales (UNSW) in Sydney, tells Mongabay. “But people in Sydney know more about the Great Barrier Reef than they know about their local kelp forests.”

Vergés says there’s also a lack of understanding about what kelp does and the value it holds, even though kelp forests play an important ecological role, acting as the “biological engine of temperate reefs.”

A new paper published in Nature Communications, co-authored by Vergés, aims to fill some of these knowledge gaps by identifying the economic value of marine kelp forests. It suggests that kelp forests across the world provide three main ecosystem services worth billions of dollars annually: the boosting of fisheries production; the removal of excessive nutrients like nitrogen and phosphorus from the water; and the sequestration of carbon dioxide.

Examining six different kelp genera (Ecklonia, Laminaria, Lessonia, Macrocystis, Nereocystis and Saccharina), the researchers find that each of these forest types generate up to $147,100 per hectare ($59,500 per acre) per year worldwide, although the exact amount varied depending on region and kelp type. Collectively, the world’s kelp forests generate up to $562 billion each year — about the same as Sweden’s entire GDP — making kelp forests about three times more valuable than previously thought, the study finds.

Most of this economic value comes from kelp forests’ contribution to fisheries production as well as the uptake of nitrogen, which generates values of $29,000 and $73,000 per hectare ($11,700 and $29,500 per acre) each year, according to the study. As for carbon sequestration, the study suggests that kelp forests sequester about as much carbon as terrestrial forests or seagrass meadows, but only contribute about $163 per hectare ($66 per acre) annually.

“The quantity of carbon that kelp forests capture and sequester is very high, and it’s similar to other very important habitats,” Vergés says. “But the value is low, and that’s just because the dollar value of carbon is low.”

Albert Pessarrodona, a marine ecologist at the University of Western Australia, who was not involved in the study, says it’s also difficult to accurately assess a kelp forest’s ability to sequester carbon since most of the carbon is locked away in the sediment — not the kelp itself.

“This means [it] is pretty challenging to estimate exactly how much carbon may be sequestered (if any), as the carbon needs to be tracked from the kelp forests (the source) to the final sink,” Pessarrodona tells Mongabay in an email. “Many scientists are currently working on establishing the methods and sequestration potential of kelp forests.”

Vergés says the study also didn’t quantify other services like tourism and coastal protection, so the overall value of about $500 billion per year is likely a “severe underestimate.”

Study lead author Aaron Eger, a marine scientist at UNSW and founder and program director of the Kelp Forest Alliance, says the primary motivation in putting together this study was to communicate the value of kelp forests to try and enable better management and protection of these ecosystems, many of which are threatened globally.

For instance, it’s estimated that 95% of the kelp forests around the Australian island state of Tasmania have died due to climate change.

“Once you can communicate that value, people care more about a kelp forest,” Eger tells Mongabay. “And governments and managing bodies can work to serve and manage those ecosystems better when they have an understanding of what’s there and how much it’s worth and how to account during the decision-making process.”

The Kelp Forest Alliance, for which both Eger and Vergés serve on the board of directors, recommends protecting 3 million hectares (7.4 million acres) and restoring 1 million hectares (2.5 million acres) of kelp forests by 2040 to support the biodiversity goals of the Kunming-Montreal Global Biodiversity Framework.

Pessarrodona praises the study for “showcasing the immense value … kelp forest ecosystems bring to coastal societies and economies.”

“This study is the first attempt at assessing the economic value of three kelp forest ecosystem services,” Pessarrodona says. “There [are] still many other ecosystem services provided by kelps that remained unassessed, and much more nuance to be provided in the services that were assessed. This study opens the door for much more exciting research in the future.”