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Introduction
Algae belong to the primitive group of plants which evolved very early in the universe. Algae are both microscopic (microalgae) and macrophytic (macroalgae) occurring in freshwater as well as marine waters. In the marine ecosystem, the micro-algae are the major primary producers and the macro-algae are called as seaweeds, which flourish on surfaces of rocks, dead coral, stones, pebbles and any other suitable substrata are available for their attachment. Macro-algae are green algae (Chlorophyceae), brown algae (Phaeophyceae) and red algae (Rhodophyceae). Seaweeds are used as human food from 600 to 800 BC. In China, seaweeds were used from prehistoric time. In China and Japan, seaweeds are used as a stable diet item for a very long period. Fresh, dried and processed seaweeds are utilized for human consumption. Many types of seaweeds are used as food in Japan, China, Philippines and other countries of Indopacific regions. Seaweeds are one of the commercially important marine living and renewable resources of India. Commercial exploitation of marine algal species commenced in India since 1966 (Oza and Zaidi, 2001). One of the reports indicates that 1518 t of (dry weight) red algae and 2285 t of (dry weight) brown algae are utilized for manufacture of agar, alginate and liquid fertilizer (Kaliaperumal et al., 2004). Seaweeds grow abundantly along the coastal waters of Tamilnadu, Gujarat, Andhra Pradesh, Orissa, West Bengal, Kerala, Maharastra, Lakshadeep and Andaman Nicobar Islands. There are also rich seaweed beds around Mumbai, Ratnagiri, Goa, Karwar, Vizhijzn, Pulicot and Chilka. Among the 20,000 species of seaweeds enumerated in the world, 271 genera and 1153 species are present in India with a total standing crop of 6, 77, 309-6, 82, 759 t fresh (Subba Rao and Mantri, 2006). According to Anantharaman et al. (2006), the total potential seaweed wealth is 8, 70,000 t fresh, present natural collection is 22,000 t fresh and through seaweed cultivation is 150 t dry. Natural habits of some of the prominent marine algae are presented in Fig. 1.
Fig. 1.
Some common medicinally important seaweeds. fam. Chlorophyceae: (a) Ulva retivulata, (b) Caulerpa racemosa; fam. Phaeophyceae: (c) Sargassum tennerium (d) Padina gymnospora; fam. Rhodophyceae: (e) Gracillaria edulis, (f) Acanthophora spicifera.
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