Seaweed Farming in Chwaka Bay: A Sustainable Alternative in Aquaculture?

In Chwaka Bay, aquaculture (the farming of aquatic organisms) is represented by a small-scale but much debated activity; farming of marine macroalgae, or seaweed farming. Aquaculture as a whole dates back several millennia in areas like South-East Asia, but has during the last decades become heavily promoted as an alternative livelihood in developing countries to (i) reduce pressure on overharvested natural resources (e.g. fish stocks) and (ii) supply cheap food and income (Tacon 2001). Many promises of this “Blue Revolution” have, however, not been fulfilled, because technical know-how and experience is often lacking (Dadzie 1992; Machena and Moehl 2001), and because some of the hitherto dominating forms (for example farming of giant shrimp/prawns) have been riddled with huge sustainability problems of their own (Deb 1998; Bryceson 2002).

Seaweed farming is, in comparison to e.g. intensive shrimp farming, an alternative form of aquaculture, which has been described as “the most sustainable” form of aquaculture. This is primarily because (i) farming can be conducted in shallow coastal areas or the open ocean (instead of in dugout ponds), (ii) the seaweeds require no addition of fertilizers or pesticides, only enough light and water mo- tion, (iii) the rapid growth rate (up to 15 percent per day) results in relatively short farming cycles (Mshigeni 1976; FAO 2002), and (iv) farming generates a cash income to farmers. Most open-water seaweed farming involves two genera of tropical red algae (Rhodophyta); Eucheuma and Kappaphycus (Zemke-White and Ohno 1999), farmed for the extraction of carrageenan; a valuable polysaccharide used as a stabilizing, emulsifying and thickening agent in food, cosmetics and pharmaceuticals.