Quantifying the Carbon Sequestration Potential of Kelp Farming in the UKEcosystem Services

Maxine Canvin^{1, 2}, Pippa Moore¹, Dan Smale²

¹Newcastle University, UK, ²The Marine Biological Association of the UK, UK

Kelp-dominated habitats are not traditionally considered Blue Carbon ecosystems. However, due to high rates of primary production and carbon export, they may serve as important carbon donors. While seaweeds, including kelp, have been historically hand-harvested in the UK, seaweed farming for various products is an emerging industry. Kelp farming may also provide additional ecosystem benefits and services, such as enhanced fisheries habitat or elevated carbon sequestration, but the evidence base remains poor. As such, quantifying carbon dynamics in and around kelp farms is crucial to determining their viability as a Blue Carbon climate change mitigation strategy. Here, rates of carbon accumulation, release (as particulate and dissolved organic carbon), burial and storage associated with Saccharina latissima was explored within a small-scale, co-cultivation (kelp and mussel) site in Cornwall, UK, using a multidisciplinary approach. Results demonstrated pronounced seasonality in productivity and release of particulate organic carbon as detritus, with a carbon sequestration rate estimated at 0.05 t CO2e ha-1 yr-1. Meanwhile, dissolved organic carbon release rates were comparatively low and highly variable between individual plants and sampling period. Examination of sediment cores from beneath and adjacent to the farm suggested burial of some kelp-derived carbon, likely increasing local carbon sequestration rates. Overall, our study shows that small-scale temperate kelp farms may enhance local carbon release and storage to some extent, but the magnitude and scale of this contribution is relatively minimal. As such, increased carbon sequestration may be considered a co-benefit or ‘stacked ecosystem service’ relating to kelp farming in the UK.