A new study finds that even as mariculture expands globally, the industry could actually decrease its current biodiversity impact by 30%—if they get smarter about where they farm. But the same study also cautions that seafood farming in the wrong locations could just as easily ramp up current marine biodiversity impacts by over 400%.
One-fifth of the fish we consume is provided by farmed seafood, and that figure is only projected to rise as global demand for protein grows. The new research, published in Nature Ecology & Evolution, calculated that mariculture—the controlled production of shellfish, bivalves, and finfish in coastal areas and in the open ocean—will need to increase by 40.5% from 108,729 hectares to 152,785, to meet this growing demand by 2050.
To understand how this expansion will affect ocean biodiversity, the team of scientists developed an impact index that considered how nutrient pollution and habitat degradation from seafood farms affect over 20,000 individual ocean species. This was based on data about species vulnerability to these pressures, and the probability that those species would occur in the vicinity of fish farms. Then the researchers developed a model to project these impacts out to 2050, according to the expected mariculture expansion. The model also took into account how a warming ocean will drive shifts in species ranges.
The result was a varied global picture showing where in the world the greatest mariculture impacts would unfold in the future—and also, where expansion would come with a lesser cost.
First of all, looking at current-day mariculture impacts, the research showed that nutrient pollution has the biggest biodiversity impact globally, accounting for almost 80% of the harms done. The modelling also showed that Southeast and East Asian countries, including China, Vietnam, Indonesia and the Philippines, have the highest concentrations of mariculture, and also the highest marine species richness overall—and in combination, that gives seafood farming in these regions the biggest biodiversity impact overall.
Under a worst-case future scenario, where mariculture expansion occurred only in biodiversity-rich regions such as these, the effects could be profound: the cumulative biodiversity impact of seafood farming would increase by an average 270% at the country level, and by 420.5% at a global scale, compared to current impacts. Species-wise, the worst affected by mariculture under this extreme scenario would be large marine mammals including whales and seals, because these animals have considerable ranges that would overlap with more open-ocean farms.
But just as there’s a worst-case scenario, the researchers also posit a best-case scenario—one we could achieve, they say, if we take a more strategic approach.
“The best case scenario refers to all mariculture farms in 2050 [being] placed in sea areas with low [impact], including relocating existing farms and the new farms,” says Deqiang Ma, postdoctoral researcher at the University of Michigan School for Environment and Sustainability, and lead author in the new study. The model showed that if farms of the future were almost exclusively sited away from biodiversity hubs, the cumulative effects of mariculture would be on average 27.5% lower at the country level compared to 2020. Taken at the global scale, that equaled an impact reduction of 30.5%. Under this best-case future scenario, almost all marine species considered in the study would experience lower impacts compared to the current-day harms of seafood farms.
“The main takeaway is that planning could substantially reduce mariculture impacts on marine biodiversity while meeting the demand for expanding mariculture,” says Ma.
This impact reversal would involve relocating almost 90% of existing bivalve and finfish farms, many of these from high-biodiversity areas currently, to low-impact zones. One location, for example, might be the waters off the United States, where there is a large untapped area available for mariculture development, and also where species richness is lower compared to, say, Indonesia.
While the study paints the possibility of marrying increased production with thriving biodiversity, the researchers picked out some caveats and concerns. The first is that while the future overhaul of mariculture would require shifting the majority of seafood farms elsewhere, the placement of these new and expanding farms must be sensitive to other needs, like those of local fishing communities who should not be displaced by new industry, the researchers urge.
Another point is that even under the model’s best-case scenario, future expansion still had some impact on marine mammals. So even if it were reorganized, mariculture would still have a cost.
The study also notes that biodiversity impacts aren’t only down to location. Bivalves like mussels and oysters double as ocean filters, actually cleansing nutrient pollution as they go, and consistently turned up as the lowest-impact form of mariculture in the research. This hints at an opportunity to move mariculture even further towards sustainability by changing the makeup of what we farm.
The researchers hope their study provides an initial guide on how to manage mariculture, before its expansion causes avoidable harm. A bit of strategic thinking, they write in their study, could “help bridge the important compromise between meeting the world’s nutritional needs and protecting the ocean’s biodiversity.”
Ma et. al. “Strategic planning could reduce farm-scale mariculture impacts on marine biodiversity while expanding seafood production.” Nature Ecology & Evolution. 2025.
Image: NOAA Sea Grant
