SEAWEED’S SOCIETAL FOOTPRINT Integrating ecosystem services into the Life Cycle Assessment framework to evaluate societal costs and benefits of seaweed farming

Sammanfattning

Seaweed cultivation is gaining attention as a nature-based solution capable of addressing food insecurity, eutrophication, and climate change simultaneously. Yet the societal costs and benefits of seaweed farming, and how they are distributed across stakeholders and scales, remain insufficiently assessed by conventional environmental tools. This study applies the Ecosystem Services Life Cycle Assessment (ES-LCA) framework developed by Rugani et al. (2019) to offshore Saccharina latissima cultivation at a farm located in Kosterhavet National Park on the Swedish west coast.The assessment follows the four-step ES-LCA structure (inventory, midpoint impact assessment, ecosystem service supply change assessment, and monetary valuation) and identifies ten CICES v5.1 ecosystem service categories affected by the farm. Seven show positive impacts, two negative, and one mixed. The farm's most significant contribution is eutrophication mitigation, generating a net credit of −2.76 kg PO₄ equivalents per tonne of fresh weight and an estimated 49.5 € of avoided external costs, directly addressing the moderate eutrophication status of the Skagerrak. The primary negative externality is the loss of recreational and aesthetic value within the national park.A spatiotemporal distributional analysis reveals a pronounced asymmetry: costs are borne locally while benefits accrue regionally and globally, with no redistribution mechanism connecting them. This raises clear environmental equity concerns and points to structural governance gaps, including the absence of payment-for-ecosystem-services schemes, ES informed marine spatial planning, and multi-level regulatory frameworks aligned with the scale of the benefits generated.The study confirms that the ES-LCA framework is operational in a marine context and highlights a cause-effect chain inaccessible with a standalone LCA or ES assessment, while identifying data gaps and methodological frontiers that define the next phase of framework development.