This factsheet presents DUC6: Lower-trophic level biomass monitoring to inform ocean governance, one of the Demonstrator Use Cases (DUCs) developed within the DTO-BioFlow project. It is intended for environmental agencies, fishing regulators, port authorities, and research institutions that are responsible for ocean governance – particularly the management of fishing quotas, marine traffic, and ecosystem health monitoring. DUC6 aims to develop a system that integrates acoustic and optical monitoring technologies to track plankton biomass more effectively, providing a comprehensive view of lower-trophic level biomass. The Demonstrator Use Cases (DUCs) are at the core of DTO-BioFlow, showcasing how biodiversity observations, AI models, and the Digital Twin of the Ocean (DTO) can deliver digital solutions for marine sustainability.