Seagrass meadows are key ecosystems for biodiversity, sediment stabilization, and long-term carbon storage (“blue carbon”). However, they are highly sensitive to anthropogenic pressures and climate change. Effective protection currently lacks reliable, high-resolution, and dynamic condition data. Current methods, such as optical remote sensing (satellites, drones) or hydroacoustic measurements (sonar), have clear limitations: they primarily deliver two-dimensional, low-resolution data or are constrained by water turbidity and low temporal density. Fine-scale 3D structures, damage, and short-term dynamics usually remain undetected. The proposed project addresses this gap through a world-first combination of drone-borne bathymetric LiDAR and ROV-based LiDAR. For the first time, a consistent 3D model spanning from the water surface to the sediment will be created. This enables the precise derivation of ecological parameters (e.g., shoot density, volume) and sets a new technological standard for the evaluation and long-term monitoring of seagrass ecosystems.