How much is a kelp forest actually worth? In 2023, a team of more than 20 researchers led by Aaron Eger at the University of New South Wales tried to answer that at a global scale, and landed on a striking number: roughly $500 billion a year, with a plausible range of $465 to $562 billion depending on assumptions about harvest rates.
To get there, the team pulled together over 1,300 fish and invertebrate surveys across six major kelp genera, including the giant kelp, bull kelp and sugar kelp familiar along different coastlines, plus 74 measurements of how fast kelp actually grows and how much carbon and nutrients it contains. They then valued three services kelp forests provide: supporting fisheries, removing excess nitrogen and phosphorus from coastal water, and capturing carbon. Nutrient removal turned out to be the single biggest driver of value, worth an estimated $73,831 per hectare per year for nitrogen alone, ahead of fisheries support at roughly $29,851 per hectare. Carbon sequestration, while real, was the smallest piece of the total, about $163 per hectare per year, adding up to roughly 4.9 megatons of carbon captured annually worldwide. Altogether, the study estimates some 740 million people live within 50 kilometers of a kelp forest.
The authors are upfront about what the number doesn’t include: wild kelp harvesting, tourism and recreation, and coastal protection weren’t part of the model, meaning $500 billion is likely an undercount rather than an overstatement. They’re also candid that the carbon figure is especially uncertain, since how much of kelp’s captured carbon actually gets locked away long-term, versus recycled back into the water, is still being worked out, the kind of question the next study on this page dives into directly. Next steps the team has flagged include better satellite mapping of exactly where kelp grows, and using chemical tracers to confirm which fish species genuinely depend on kelp habitat rather than just passing through it.
Further reading: Eger, A.M. et al., “The value of ecosystem services in global marine kelp forests,” Nature Communications (2023).