Understanding diseases and control in seaweed farming in Zanzibar

This study identifies some causes of the die-off of the seaweed types Eucheuma denticulatum (commonly known as spinosum), Kappaphycus striatum and K. alvarezii (both commonly known as cottonii) observed in the farming areas of the Zanzibar archipelago. It also makes short- and long-term recommendations to protect the farming ecosystem environment, controlice-ice disease and epiphyte infestation, and boost the seaweed industry in the island.Die-offs are mainly caused by severe cases of epiphyte infestation coupled with a high incidence of ice-ice disease, which has long been observed by farmers to intensify during the hot-dry season and diminish during the wet season. In fact, high temperatures in the farming sites, together with high-light intensity/irradiance, represent key triggers ofice-ice occurrence and epiphyte bloom. Among the recommendations provided in this study are: (i) implementing strict quarantine procedures; (ii) transferring the farming of E. denticulatum and K. striatum to deeper waters (25 m) using longlines or the raft method where practical; and (iii) using a "freshwater shock" or a commercially available anti-fouling agent to eliminate epiphytes if lagoon farming is continued during the hot-dry season