Environmental Impacts of Seaweed Farming in the Tropics

Seaweeds are multicellular algae that occur in marine and brackish-water and that, at some stage in their lives, are attached to a substrate. World-wide there are approximately 10,000 species of seaweeds and at least 221 species of seaweed are utilised by humans. 145 species are used for food while 101 species are used for phycocolloid production (i.e. alginates, agar and carrageenan). Each year around 2 million tonnes dry weight (approximately 13 million tonnes fresh weight) of seaweed is collected at a value of in excess of US$6.2 billion. 50% of this seaweed (by volume) is cultured and approximately 10% of cultured seaweed comes originates in the tropics. In the tropics the vast majority of seaweed farmed is of the genera Eucheuma or Kappaphycus. Approximately 120,000 tonnes dry weight (t dw) of Eucheuma/Kappaphycus are produced annually compared with approximately 15,500 t dw of Gracilaria and 800 t dw of Caulerpa (Zemke-White and Ohno 1999). Most of the Eucheuma/Kappaphucus is farmed in the Philippines (~95,000 t dw), followed by Indonesia (22,000 t dw), Zanzibar (4,000 t dw), Malaysia (800 t dw), Kiribati and Madagascar (both around 400 t dw). Most of the Gracilaria is farmed in Indonesia (~13,500 t dw) and almost all of the Caulerpa is farmed in the Philippines.