Mass cultures of marine macroalgae (seaweeds) in the sea or on land serve as an "nutrient extracting aquaculture" reducing eutrophication along the Chinese coast or purifying outflow from intensive fish farms in Israel. This beneficial side-effect of seaweed cultures is also used in the recently SEAPURA project fundet by the EU and coordinated by the Wattenmeerstation Sylt (AWI). Outdoor tank cultures of commercially important, perennial red seaweed species are used for extracting nutrients from fish farms in Spain and Portugal, and accompanying research is conducted in Germany and Northern Ireland. The cultivated seaweed biomass will be used for for the human food market mainly in France, for extraction of pharmaceutical substances, or for fish feed additives, with possible antibiotic effects of the cultivated seaweed. Continuous short-day treatment with automatic blinds on top of the cultivation tanks will be used for year-round activation of cell division in the cultivated red algae for preventing the naturally occurring summer dormancy of perennial seaweeds.