This chapter places seaweed production and use within a broader sustainability and value-chain perspective. Building on the preceding chapters, which addressed nutrients, food safety, processing technologies, sensory quality and consumer acceptance, this chapter examines how seaweed cultivation and utilisation align with European sustainability objectives, environmental policy frameworks, and emerging blue-bioeconomy strategies. It synthesises current evidence on environmental performance, nutrient and carbon dynamics, and life cycle impacts, and discusses how these factors influence the long-term viability and credibility of the European seaweed sector. Attention is given to the distinction between conceptual environmental potential and verifiable, measurable sustainability outcomes across the value chain.
7.1. European framework for sustainable blue growth and seaweed cultivation
EU sustainable targets
The EU aims to achieve sustainable and inclusive growth through the European Green Deal (European Commission 2019), which outlines measures to mobilize public and private investment toward climate and environmental goals. The overarching target is climate neutrality by 2050 (European Commission 2018), with legally binding interim goals such as a 55% reduction in greenhouse gas emissions by 2030 (EU 2021/1119). Similarly, the revised Urban Wastewater Treatment Directive (EU 2024/3019) requires member states to cut emissions of total phosphorus and nitrogen by 75% by 2025, and by up to 87.5% and 82.5%, respectively, by 2045.
Seaweeds and the blue bioeconomy
To mitigate climate change and reduce pressure on terrestrial food production, the EU increasingly recognizes the role of the oceans and promotes a transition from “blue growth” to a sustainable blue economy (European Commission 2021a). Within this framework, seaweeds are identified as renewable biomass sources that can provide environmental and health benefits (European Commission 2022). The European Commission actively supports seaweed cultivation through the Sustainable Development of Aquaculture Strategy (European Commission 2021c), the Organic Production Action Plan (European Commission 2021b), and funding mechanisms such as the European Maritime, Fisheries and Aquaculture Fund (EMFAF) under the BlueInvest initiative, which has supported nearly 100 algae-focused companies (Carboni et al. 2025). Despite this momentum, European seaweed cultivation remains a nascent industry, mainly focused on at-sea farming of kelps (e.g. S. latissima, A. esculenta), with smaller pilot-scale efforts on Ulva spp. and P. palmata in land-based or IMTA systems (Barbier et al. 2020; Araújo et al. 2021). In 2022, European seaweed aquaculture produced approximately 1,040 t (wet weight) with a value of €6.3 million, of which some Nordic countries (i.e., Norway, Faroe Island, Denmark) contributed for 33% (Rebours and Sánchez López 2023).
EU water and nutrient policies
Recent EU policy discussions increasingly emphasise on carbon storage and alternative protein production from seaweed. In contrast, the potential of seaweed cultivation as a marine mitigation measure for nutrient recovery, particularly nitrogen (N) and phosphorus (P), remains insufficiently recognised. Existing key regulatory frameworks such as the Water Framework Directive (European Parliament and EU Council 2000), Nitrates Directive (European Parliament and EU Council 1991), and Marine Strategy Framework Directive (European Parliament and EU Council 2008) primarily conceptualise seaweed as indicators of eutrophication or symptoms of eutrophication rather than as active tools for nutrient removal. Large-scale field evidence now demonstrates that cultivated seaweeds can contribute measurably to nutrient uptake and removal, albeit at site-specific efficiencies and with clear spatial limitations (Bruhn et al. 2025). Although the revised Urban Wastewater Treatment Directive strengthens nutrient removal requirements, it does not yet integrate marine biomass production, such as seaweed farming, into broader nutrient management or mitigation strategies. This represents a missed opportunity to link water policy objectives with emerging blue-bioeconomy solutions.
Environmental value of the seaweed sector
Within the framework of the Circular Economy Action Plan (European commission 2020) and the emerging EU Circular Economy Act, seaweeds have been increasingly highlighted as a nature-based solution with potential to support nutrient recovery, recycling and more resource-efficient food systems. Seaweed cultivation is frequently associated with multiple environmental co-benefits, including uptake of dissolved nutrients, low input requirements, and compatibility with integrated multi-trophic systems. However, while the conceptual potential of the sector is well recognised, robust and comparable scientific evidence quantifying its net contributions, particularly with respect to long-term carbon sequestration and nitrogen and phosphorus removal at relevant spatial scales, remains limited and highly context dependent. Recent assessments emphasise that environmental benefits from seaweed cultivation depend strongly on species, cultivation density, site characteristics, hydrodynamics, and the fate of harvested biomass, and therefore cannot be assumed uniformly across production systems (Bruhn et al. 2025). Demonstrating measurable, verifiable and site-specific environmental outcomes will be essential if the seaweed sector is to credibly position itself within EU sustainability frameworks. In this regard, improved monitoring, harmonised metrics and transparent reporting of nutrient removal and carbon flows will be key to aligning seaweed production with the environmental sustainability criteria of the EU Taxonomy for sustainable activities (European Parliament and EU Council 2020). While EU policy frameworks increasingly frame seaweed cultivation as a potential contributor to climate and nutrient objectives, the extent to which these ambitions can be realised depends on the underlying biogeochemical functioning of seaweed systems. Understanding the carbon and nutrient dynamics of cultivated seaweeds is therefore essential to assess their realistic mitigation potential.
7.2. Carbon and nitrogen removal potential of seaweed
The potential of seaweed cultivation to contribute to nutrient removal and climate mitigation is closely linked to its carbon and nitrogen dynamics, which vary across species, cultivation systems and environmental conditions.
The carbon-to-nitrogen (C:N) ratio of seaweeds has been used as an indicator of nutrient level in many studies (Chapman and Craigie 1977) and reflect nutrient conditions and climate adaptation throughout the growing period. C:N ratios are also fundamental for understanding many oceanic biogeochemical processes, such as nutrient flux and climate regulation (Sheppard et al. 2023). Kelp species can utilize ammonia instead of nitrate, making these seaweed good candidates for integration into an integrated multitrophic aquaculture system where predominantly ammonia-rich effluents are released from fed aquaculture (Handå et al. 2013; Wang et al. 2014). Similarly, the potential of the cosmopolitan and euryhaline genus Ulva has also been well documented for bioremediation of nutrients with high efficiency for uptake (from 40% up to 90%) resulting high biomass yield (40–100 g of DW m-2 day-1) (Neori et al. 2004; Bruhn et al. 2011; Nielsen et al. 2012; Lubsch and Timmermans 2019) with preferences for ammonium (Vandermeulen and Gordin 1990; Hernández et al. 2002). Furthermore, seaweed systems, both natural ecosystems and aquaculture, have been considered potential contributors to carbon dioxide removal (CDR) and climate mitigation (Duarte and Cebrián 1996). This expectation results partly from the hypothesis that seaweed productivity exceeds that of terrestrial plants (Froehlich et al. 2019; Yong et al. 2022). However, there is still non-consensus on whether seaweed systems act as net carbon sinks or sources. Evidence shows that natural ecosystems often exhibit high carbon fluxes and are generally net autotrophic, comparable to or exceeding other vegetated coastal habitats (Filbee-Dexter et al. 2023). Yet, other studies indicate that they can be net heterotrophic, functioning as CO2 sources when their productivity depends on organic carbon from external sources (Gallagher et al. 2022).
Carbon dynamics
In aquaculture, seaweeds may also act as temporary carbon stores rather than long-term sinks, since biomass is typically consumed as food or feed, leading to rapid carbon remineralisation (Fujita et al. 2023). Consequently, Hurd et al. (2022) advocate for a “forensic analysis” of carbon flows in seaweed systems to quantify organic carbon fluxes and storage. This is particularly important because seaweeds have short production–consumption cycles and can release substantial amounts of dissolved and particulate organic carbon, as well as very short-lived halocarbons, e.g., bromoform (CHBr3), methyl iodide (CH3I) and diiodomethane (CH2I2), which can alter the ozone layer and biogeochemical cycles (Stemmler et al. 2015; Keng et al. 2020). Understanding their sources, quantifying emissions, and addressing existing knowledge gaps is therefore essential in the context of expanding seaweed aquaculture in a changing climate (Keng et al. 2020).
Although seaweeds can assimilate carbon and nutrients during growth, the environmental significance of this uptake depends on how biomass is harvested, processed and used. Evaluating the sustainability of seaweed-based products therefore requires a full value-chain perspective, which is commonly addressed through life cycle assessment (LCA).
7.3. Sustainable value-chain design
Life Cycle Assessments (LCAs) play a central role in corporate sustainability, policy development, and assessing seaweeds’ contribution to the wider bioeconomy. Current global seaweed cultivation practices are associated with low emissions, typically 0.02–0.08 kg CO₂-eq. per kg wet seaweed, with key environmental hotspots arising during processing (particularly drying), transport, and the use of farm infrastructure such as ropes (Seghetta et al. 2016; Waqas et al. 2024; Thomas et al. 2024). Seaweed farming is therefore considered among the lowest greenhouse gas (GHG) “blue foods” (Gephart et al. 2021). However, thermal drying and freezing remain major contributors to impacts (van Oirschot et al. 2017; Thomas et al. 2021). Environmental performance is strongly influenced by the energy source used for drying (Error! Reference source not found.) as well as by farm scale, which affects the relative contribution of drying, transport, and storage (Koesling et al. 2021). Packaging and transport typically add 5–20 kg CO₂ eq. per tonne of fresh seaweed. Lower values correspond to short transport distances, efficient logistics, and lightweight packaging, while higher values are associated with long-distance road transport across Europe, refrigerated distribution, or more material-intensive packaging solutions (Seghetta et al. 2017; Thomas et al. 2021).