Seaweed is used as a source of potash fertilizer. Such as Spirulina, Scytonema, Oscillatoria, Anabaena, Nostoc etc.
10. Determining the location of spy submarines: Blue-green algae contain pigment particles called phycobilin protein. These pigment particles (C-phycoerythrin, C-phycocyanin) absorb the diffracted rays from spy submarines. The location of the spy submarine is determined by the amount of absorbed radiation.