Green Algae Bloom

A green algae bloom is a proliferation of green macroalgae, most often Ulva species, that forms floating or stranded mats known as green tides. Driven by nitrogen and phosphorus enrichment in sheltered, shallow coastal waters, Ulva sheets and filaments accumulate into biomass that can blanket beaches and tidal flats. The Yellow Sea green tide off Qingdao is the largest documented, covering thousands of square kilometers of Ulva prolifera each summer. Decaying mats consume oxygen, smother benthic habitat, and release hydrogen sulfide and ammonia as they rot, posing a public-health nuisance. Green tides are a recognized eutrophication symptom under WFD and OSPAR macroalgae assessments.