Seaweeds or macroalgae belong to the lower plants, meaning that they do not have roots, stems, and leaves. Instead they are composed of a thallus (leaf-like structure) and sometimes a stem and a foot. Macroalgae represent a diverse group of eukaryotic, photosynthetic marine organisms. Unlike microalgae, which are unicellular, the macroalgal species are multicellular and possess plant-like characteristics. They are typically composed of a blade or lamina, the stipe, and a holdfast for anchoring the entire structure to hard substrates in marine environ­ments. The general features of these structures are very diverse in the various taxa comprising macroalgae. There are forms of which the primary feature comprises long blades, forms that are branched, and others that are leafy and that form mats. Moreover, some forms possess air bladders that act as flotation devices that enable some species to stand upright or occur free — floating on ocean surfaces. They are often fast growing and can reach sizes of up to 60 m in length (McHugh, 2003). They are classified into three broad groups based on the composition of photosynthetic pigmentation: (1) brown seaweed (Phaeophyceae), (2) red seaweed (Rhodophyceae), and (3) green seaweed (Chlorophyceae). Seaweeds are mainly utilized for the production of food and the extraction of hydrocolloids.