Why Earth’s giant kelp forests are worth $500 billion a year

The vast swathes of kelp forest growing along the world’s coastlines are estimated to generate US$500 billion a year on average, making them considerably more valuable than previous studies have suggested, according to an analysis that assessed economic contributions made by six types of the seaweed.

The study, published on 18 April in Nature Communications¹, estimates that kelp forests provide services worth between $465 billion and $562 billion a year worldwide, mainly by providing a habitat for valuable fish and seafood species, and by removing nitrogen from contaminated seawater. The results suggest that each type of kelp forest (see ‘Seaweed services’) generates up to $147,100 per hectare annually, a figure that’s more than three times higher than previous estimates.

“Until now, most kelp-forest evaluations were regional,” says Cristina Piñeiro-Corbeira, a marine ecologist at the University of A Coruña in Spain who was not involved in the project. “This study is a step forward in understanding kelp forests and their importance for human well-being on a global scale.”

Kelp forests are widespread in temperate and polar regions, with some 740 million people thought to live within 50 kilometres of one of these tracts of brown seaweed. They provide habitat for more than one thousand species, draw carbon dioxide from the atmosphere and help to remove nutrient pollution, such as nitrogen and phosphorus, from the ocean. “Outside of the tropics, kelp forests are really the dominant [coastal] habitat,” says study co-author Aaron Eger, a marine scientist at the University of New South Wales in Sydney, Australia. “These are the essential threads to marine ecosystems.”

Despite this, few studies have attempted to quantify the economic value of kelp forests on a global scale. To address this gap, Eger and his colleagues assessed the value of common types of kelp forest by considering their contributions to fisheries, nutrient cycling and atmospheric CO₂ removal. They collated kelp-distribution estimates, data from biodiversity surveys and current seafood prices from different regions.

The team’s estimates suggest that kelp forests provide an average harvest for fisheries of more than 900 kilograms per hectare a year, worth about $30,000. In many locations, lobsters and abalone accounted for more than one-quarter of a kelp site’s fisheries value. Pollack, giant seabass, South American morwongs and lingcod were the most valuable fish across the sites surveyed.

Each hectare of kelp forest also removes an average of 657 kilograms of excess nitrogen — which flows into the ocean in waste water and agricultural runoff — from seawater, a service worth almost $74,000 per hectare per year. And together, kelp forests absorb almost five megatonnes of atmospheric CO₂ each year, putting them on a par with other prominent carbon sinks, such as mangrove forests and terrestrial woodland. The economic value of this carbon removal is only $163 a year per hectare of kelp, however, owing to the low market price of carbon and its widespread presence in the ocean, says Eger. “The impacts of nitrogen are quite localized, so there is a higher demand to address the problem,” he says. “Carbon is diffuse and hard to attach to damages in any one location.”

Kelp conservation

Piñeiro-Corbeira says the findings could provide a push for kelp forests to be included more prominently in climate-change policies and could also encourage better ways of managing and conserving them. But she adds that because the study focuses on only three ecosystem services, it could still underestimate the value of kelp forests.

The inclusion of other services — such as coastal protection, tourism and recreation — in the models is likely to further boost kelp forests’ estimated value, says Eger. The value might also increase as more areas are mapped and researchers gain a better understanding of how much kelp is in the ocean. “It has a strong potential to go up,” he says.

Source: Ecology - nature.com