34 December 2011 Environmental changes and their impact on seaweed farming in Tanzania Flower E. Msuya1 When seaweed farming started in Tanzania in 1989, the two species that are farmed commercially, Eucheuma denticulatum (spinosum) and Kappaphycus alvarezii (cottonii), were thriving with no differences in growth (Msuya in press). Recently, however, there differences in the growth of the two species have been observed, with one species, cottonii, being severely affected by changes in environmental conditions, leading to die-offs. The possible causes of the die-offs are stated in Msuya (this issue of World Aquaculture). The other species, spinosum, is not much affected though some seasonal reduction in growth has been observed. The impact and effects of the die-offs are shown by changes in production of the species, change in number of farmers, use of cultivation sites, fouling and effect on community services. In this article, effects of the changes in environmental conditions on the above mentioned issues as well as efforts to curb (or cope with) those conditions are discussed. Effects on Seaweed Production The effect of environmental changes on the production of cottonii is shown by the severe decline in seaweed production in areas where much of that species was previously produced. One such area is Songosongo island2 in southern Tanzania (Figure 1), an island that had a village that produced large volumes of cottonii. In addition, seaweed farming in Songosongo, just like in other parts of Tanzania, had proved to be an important for the livelihoods of the people. However, the village severely hit by die-offs of cottonii has seen its seaweed production decreasing drasFig. 1. Map of Tanzania coast showing the seaweed farming areas. tically since 2004. Production varied from an annual tonnage of 420 t dry seaweed worth about US$60,000 during the peak in 2003 to 26 t in 2008 worth only US$3,000. This has had disastrous effect on the farmers who were depending for much of their income from farming seaweed. A similar situation was observed in Zanzibar where farming of the species has failed in many areas where it used to grow. Combining the failure of cottonii and low price obtained from spinosum (Msuya in press), production of cottonii has severely decreased over the years; for example from 1,048 t in 2001 to 16.5 t in 2008. In mainland Tanzania, production of cottonii in all the cultivation sites has also decreased in recent years. According to the Department of Aquaculture statistics, production of cottonii decreased from 1,500 t in 2003 to 887 t in 2008/2009. Effects on Seaweed Farmers Use of cultivation sites. The farmers have been practicing “shift cultivation,” in which they move from one farming site to the next trying to see if the seaweed will grow. In Songosongo, for example, farmers have been changing the cultivation sites when they observed that production is failing (Msuya and Porter 2009). Whereas, seaweed was previously planted throughout the island, the cultivation sites are now concentrated on the southern part of the
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