Red algae contains the pigment phycoerythrin  Phycoerythrin reflects red light and absorbs blue light  As blue light has the ability to penetrate water to great depths, phycoerythrin allows red algae to absorb the light needed to produce the fuel essential to their survival  Because of their need for light, red algae cannot survive in waters where the surface is covered with other plant life or debris
300 years ago, Japanese cultures began cultivating red algae for food
Red algae was not cultivated in Japan until 300 years ago.