Determining the contribution of temperate seaweed farming to local sedimentary carbon stocks and climate change mitigation

Seaweed farming, often regarded as a low-impact aquaculture practice, may deliver ecosystem services like carbon sequestration. Yet, empirical evidence for its climate change mitigation potential is limited. Sediment cores were collected at increasing distances from a seaweed farm in southwest UK and analysed for carbon stocks, carbon sedimentation rates, potential carbon sources, and sediment characteristics. The upper 3 cm of sediment, linked to farming activity, held ~2 t C_org ha^-1 with sedimentation rates of 0.23 t C_org ha^-1 yr^-1. eDNA revealed low, inconsistent contributions of kelp and mussels, while seagrass, red algae, and likely phytoplankton, dominated. The sedimentary environment remained largely unchanged pre- and post-farm establishment or with increasing distance from the farm, highlighting the limited carbon sequestration potential at this scale. Future research should focus on identifying potential carbon sinks through hydrodynamic modelling and sediment analysis to inform the climate-conscious, sustainable industry expansion.