In their natural environment, macroalgae grow on rocky substrates and form stable, mul­tilayered, perennial vegetation, capturing almost all available photons. Due to the fact that seaweeds are fixed to their substrate, values for maximum productivity may be 10 times higher for a seaweed stand than for a plankton population and can be as high as 1.8 kg C m~2 y_1. Commercial farming of seaweed has a long history, especially in Asia. The kelp Laminaria japonica is the most important, with 4.2 million tons (Mio. t) cultivated mainly in China (Luning and Pang, 2003). Approximately 200 species of seaweeds are used worldwide, about 10 of which are intensively cultivated, including the brown algae Laminaria japonica and Undaria pinnatifida; the red algae Porphyra, Eucheuma, Kappaphycus, and Gracilaria; and the green algae Monostroma and Enteromorpha (Luning and Pang, 2003).