Lush kelp forests that line long stretches of the world’s coastlines provide huge ecosystem services that benefit humanity to the tune of $500 billion a year.
This striking figure comes from the first ever global economic assessment of these macroalgae, finding that especially when it comes to providing habitat that supports fisheries and slurping up nitrogen pollution, these ecosystems have an enormously under-appreciated value in our lives.
There are over 100 kelp species, some of which grow as tall as the tallest rainforest trees, and fringe 25% of global coastlines. For millennia people have used kelp itself as a food source, or relied on it for the marine biodiversity its thicket-like ecosystems support. Kelp has cultural and recreational importance, too. Yet until now there have been no thorough estimates of its value—which matters because we have no sense therefore of what the hidden costs of losing these underwater forests might be.
Valuing these ecosystems economically ‘is just an additional tool for people to understand, and for us to communicate, the importance of these ecosystems,” says Aaron Eger, a marine scientist at the University of New South Wales, and lead author on the new Nature Communications study.
Eger and team reached their estimates by first of all mapping out the occurrence of six major kelp genera across the ocean—from the North Pacific to the South Atlantic. Then, for each kelp type and region they were able to estimate what these forests contribute to three key ecosystem services: providing habitat to support fisheries, absorbing nitrogen pollution, and sequestering carbon. (Kelp does many other things including buffering coastlines against storms, but this was beyond the remit of the study to explore.)
Using current market rates—i.e. the dollar amount paid in 2020 for a carbon credit, for the clean-up associated with pollution, and to fishers for their catch—the researchers could then attach a value to these ecosystem services.
From this dataset, the researchers calculated that each of the six kelp genera produce services with a potential value of between $64,400 and almost $150,000 per hectare, per year—threefold more than the per-hectare value that previous studies have estimated. All together, this puts the value of global kelp forests at between $465 and $562 billion each year. Averaged out, that’s a not inconsiderable $500 billion annually.
Most of this figure is thanks to fish and the capture of nitrogen. The commercial capture of fish species that wouldn’t exist without kelp habitat amounts to a potential value of almost $30 million per hectare of kelp forest, per year. Meanwhile, the biggest economic benefit comes from the capacity of nitrogen pollution-slurping kelp fronds to absorb almost $74 million per hectare per year in would-be clean-up costs.
The amount of carbon that kelp forests lock away proved trickier to estimate, because there are still-evolving scientific estimates about what share of the carbon that kelp sequesters in its fronds is then released when the seaweed washes ashore and decays, or is permanently contained when kelp sinks into the deep sea.
To get around this the researchers made a highly conservative calculation, calculating what would happen if just 10% of the carbon that kelp absorbs gets permanently locked in. They determined that over the course of 30 years global kelp forests could therefore lock away between 14 and 292 megatons of carbon, putting these ecosystems on a par with others like seagrass meadows and terrestrial forests.
Yet, this carbon potential represents the lowest economic returns of the three ecosystem services the study investigated—just $163 per hectare per year—partly because of the low market value of carbon credits. It’s a reminder, the researchers say, not to value ecosystems by their carbon offset potential alone, because this can limit our appreciation of the full scope of benefits they provide.
Throughout the study they frame kelp’s huge economic contribution only as a ‘potential’ benefit. The main reason for this is that most of kelp’s ecosystem services currently aren’t given any real-world economic value. Its pollution-clearing potential, fish provision, or carbon storage have no formal place in markets; in many ways, we currently take these services for granted. And yet if kelp were to disappear, it would undoubtedly leave immense costs for us to pay in lost fisheries, pollution clean-up, and the climate impacts of more carbon emissions.
The researchers hope that putting a financial value on these services—building on top of kelp’s intrinsic cultural, recreational, and social value—will increase the momentum to protect these forests. “As governments and businesses around the world look to expand the ‘blue economy‘, I think now there’s a nice opportunity to value nature,” Eger says. “When we have these sort of evaluation figures, we can start to invest in and protect nature—kelp forests, in this case.”
Eger et. al. “The value of ecosystem services in global marine kelp forests.” Nature Communications. 2023.
Image: ©Anthropocene Magazine
