A survey was carried out along the intertidal and subtidal areas of the Gulf of Mannar (from Rameswaram to Tuticorin) to identify places of seaweed abundance, to study seaweed species diversity and document rare/threatened/ endemic species, to identify localities where commercial harvest of seaweed is being undertaken and to recommend areas for sustainable seaweed harvesting. 99 species were recorded, of which 21 were classified as rare. Gracilaria edulis which was abundant earlier is now rare due to over exploitation and is listed as endangered. Harvesting of Sargassum and Turbinaria could be continued to be allowed as both seaweeds have rich biomass. Meeting of scientists and seaweed collectors may be arranged periodically to explain about the importance of sustainable harvesting and GOMBRT should make efforts to involve the seaweed industry as a partner in the cultivation of commercial seaweed.