Monitoring seaweed aquaculture in the Yellow Sea with multiple sensors for managing the disaster of macroalgal blooms

Multi-sensor remote sensing is a critical part of the surveillance of coastal ocean for hazard management. The world's largest green macroalgae blooms (green tide) in the Yellow Sea since 2007 are caused by the macroalgae of Ulva, which are disposed as biofoulings into sea water when workers recycle seaweed (Porphyra) farming facilities. We traced the development processes of seaweed cultivation in which area since 2000 and the variation in macroalgal blooms since 2007 through multi-sensors (satellite, Unmanned Aerial Vehicle, and ground spectroradiometer) remote sensing in this study. We found that the sudden occurrence of large-scale green tide in 2007 and the increasing trend since that year were caused by the seaweed aquaculture in a specific mode at specific locations. A numerical simulation and satellite observations on the relationship between the timing of recycling seaweed facilities and the volume of green tide suggest that the green tide is manageable. Adoption of multi-sensor, multi-scale, and multi-temporal observations, translocating seaweed farming sites, and changing the cultivation mode are deemed as key tools for controlling the green tide and sustaining the seaweed aquaculture.