n order to warrant the food security for ten billion people in about 40 years the production of proteins is essential. It happens to be that the protein content and composition of certain seaweeds is such that it is suitable for human food. With regard to the daily need of good quality protein per individual, to protein content as percentage of dry matter, we calculated that no more than 2% of the worlds’ ocean surface is sufficient to produce the proteins for 10 billion people. It is, however, still 360,000km2 of seaweed-based seafarms. In order to do it sustainable, meaning economically feasible, ecologically sound (restoring habitats) and societally accepted, we need at the same time to yield also other components like sugars, the emulsifiers, lipids, etc., we need to sequester GHGs, we need to recycle micronutrients and phosphorus, in short, all elements we already lost to the sea. We have to design seafarms in such a way that they contribute, e.g., to coastal defence.