The growing narrative positioning seaweed aquaculture as a climate solution and a tool for ecosystem restoration is not supported by robust evidence. A meta-analysis published in Reviews in Fisheries Science & Aquaculture concludes that while seaweed farming can contribute to water quality improvement, there is insufficient evidence to confirm consistent benefits for climate regulation or biodiversity.
The study, which reviews 134 studies across 30 countries, questions one of the sector’s key value propositions: its role as a carbon sink.
According to the authors, seaweed aquaculture can accumulate a median of 1,546 kg of carbon per hectare per year in biomass, with lower estimates for long-term carbon burial or deep-sea export (725 kg C/ha/year) and even more limited net mitigation (384 kg C/ha/year).
However, these figures show high variability and are strongly dependent on environmental and operational conditions.
Crucially, the study highlights major uncertainties regarding the ultimate fate of the carbon fixed by seaweeds. A significant proportion may be rapidly remineralised or returned to the atmosphere, while emissions associated with harvesting, processing and supply chains can offset part or all of the potential climate benefits.
As a result, the authors caution that seaweed aquaculture cannot be universally considered a net carbon sink, particularly in the absence of industrial-scale life cycle assessments.
In contrast, the evidence for water quality regulation is more consistent. Seaweeds can remove dissolved nutrients from the water column, with median values of 83 kg of nitrogen and 23 kg of phosphorus per hectare per year. This function is particularly relevant in integrated multi-trophic aquaculture (IMTA) systems and in eutrophic coastal environments.
Findings on biodiversity are far more variable. While seaweed farms can provide habitat for a range of species, there is no clear evidence that they enhance biodiversity compared to natural ecosystems such as seagrass meadows or kelp forests. In some cases, neutral or even negative effects have been reported.
The study attributes much of this uncertainty to the lack of standardised methodologies for assessing ecosystem services, as well as to the high variability across species, locations and farming systems.
In this context, the authors suggest a shift in perspective: environmental benefits linked to seaweed farming — particularly climate regulation and biodiversity — should be considered potential co-benefits of biomass production, rather than its primary justification.
The paper also highlights the need for robust Monitoring, Reporting and Verification (MRV) frameworks and long-term data to properly assess the sector’s real impact at scale.
Reference:
Swanlund, H., Burrows, M. T., Fedenko, J., O’Dell, A., & Hughes, A. D. (2026). A review and meta-analysis of the ecosystem service enhancement from seaweed aquaculture: Limited evidence to support climate and biodiversity gains. Reviews in Fisheries Science & Aquaculture. https://doi.org/10.1080/23308249.2026.2647211
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