Having it all: Protecting biodiversity, carbon capture, and fish stocks

Image of a fishing boat.

Right now, only 2.7 percent of the ocean is part of a marine protection area, a far cry from the goal of 30 percent by 2030 that many countries have pledged to reach. But even as the coastal nations of the world begin to make headway on adding protections, a group of researchers is pretty sure it has found a better way of going about things.

The group’s research, recently published in Nature, suggests ways to optimize marine protected areas around the globe. The study, done by more than two dozen international researchers, offers insight in the best ways to bolster fish population, biodiversity, and carbon sequestration potential in the ocean.

“The world has decided to invest more into marine protected areas, and we want to make sure that there is a good return on that investment, and for that we need a plan,” said Boris Worm, one of the paper’s authors and a marine biologist at Dalhousie University in Nova Scotia.

Divide and analyze

The research, which began three years ago, saw the large team divvy the oceans into thousands of parcels, each 50 km x 50 km, and analyze environmental data for every one of them. On this fine-scale maritime map, the researchers identified cells that provided benefits to the oceans.

The first of the benefits they looked at is biodiversity. The second is an area’s benefits to fish stock—its ability to enable more fish to spawn. According to the Food and Agriculture Organization (FAO), 90 percent of marine fish stocks in 2018 are either depleted, overexploited, or fully exploited. The third quality is the parcel’s capacity to sequester carbon in its sediment. Some of the team’s researchers previously mapped the carbon sequestration potential of different parts of the ocean, and they found that ocean sediments can sequester more than twice the amount that terrestrial soils can.

The west coast of Vancouver Island in Canada, as an example, has all three attributes. It has a healthy amount of biodiversity. It also is very productive in terms of fish, and when these fish die, they sink to the bottom of the ocean, taking their carbon with them, Worm told Ars.

The team identified which parcels were hot spots for one, two, or all three of these features. The paper shows that only 0.3 percent and 2.7 percent of the ocean have three or two of these factors, respectively. The researchers then developed an algorithm that allows them to maximize the benefits of each zone using marine protected areas. According to Worm, this research could help the world’s governments get the most out of their efforts to protect ecosystems in their waters and the ocean as a whole.

“In the end, we brought it all together to try to understand how the protection of any parcel of ocean space in the world would affect those three objectives: biodiversity, fisheries, and carbon,” Worm said.

The algorithm allows users to weigh the objectives however they like and then provides them with the optimal network to do so—the smallest area you would need to protect to fulfill those objectives.

Less space, more benefits

Hypothetically, if the world’s governments wanted to maximize for biodiversity, they would need a strategically located 21 percent of the ocean placed under marine protected areas. This would raise the average protection of endangered and critically endangered species from their current rates of 1.5 and 1.1 percent to 82 and 87 percent, respectively, the paper notes. This form of optimization would, coincidentally, protect 89 percent of at-risk carbon sequestering areas in the oceans.

Those protections would also come at a cost: 27 million metric tons of catchable fish would be off-limits. According to the FAO, in 2018, 84.4 million metric tons of fish were caught, though research from 2016 suggests that many metric tons of fish go unreported each year. “There are co-benefits, but you can’t optimize everything at the same time necessarily. There are some trade-offs, but they are limited trade-offs because you have these co-benefits,” Worm said.

There’s also an option to deploy the algorithm to optimize all three outcomes, weighed according to the users’ priorities. For example, to weigh food production and biodiversity the same would require protecting 45 percent of the ocean and yield 71 percent of the maximum biodiversity benefits and 92 percent of food benefits—but just 29 percent of carbon benefits. “That’s where you’re trying to find the sweet spot where you get the most return on the investment across all three objectives,” he told Ars.

Further, though the algorithm could be used for each country’s individual coastal waters, it is roughly twice as effective when applied globally, rather than piecemeal. “There are large efficiency gains if the global community were doing this in a coordinated approach,” he said.

To get the full benefits of these optimizations, the targeted regions would need to be wholly free of industrial development and extraction. However, not all marine protected areas have been entirely free of human use. A 2018 study penned by Worm, among others, suggests that trawling for fish is still commonplace—59 percent of marine protected areas in Europe are regularly trawled.

Nature, 2021. DOI: 10.1038/s41586-021-03371-z  (About DOIs).

Doug Johnson (@DougcJohnson) is a Canadian freelance reporter. His works have appeared in National Geographic, Undark, and Hakai Magazine, among others.