Content area
Full text
Abstract
Since 2011, seaweed farmers and traders have experienced serious decreased production and income. This study identifies some causes of the seaweed die-off of Eucheuma denticulatum (commonly known as spinosum) and Kappaphycusstriatum and K. alvarezii (both commonly known as cottonii) observed in the farming areas of Unguja and Pemba (Zanzibar archipelago). It also makes short- and long-term recommendations to protect the farming ecosystem environment, control (prevention and mitigation) of ice-ice disease and epiphyte infestation, and boost the seaweed industry in the island.
Die-offs are mainly caused by a severe case 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. High temperature in the farming sites (29.5-35.5 °C) is determined as one of the main triggers of the ice-ice occurrence as well as the bloom of epiphyte infestation. Another factor is high light intensity/irradiance. As seaweed farming in Zanzibar is mainly done in shallow intertidal lagoons, seaweeds are almost in direct contact with the bottom substrate during low tides and hence exposed to higher levels of temperature and light intensity. This combination predisposes seaweed to opportunistic pathogens, manifesting the thalli whitening popularly called ice-ice disease. Bacterial infection leads to softening of the thalli and to their eventual fragmentation.
These infestations and diseases are a continuing threat to the commercially farmed eucheumoids and makes seaweed production in Zanzibar to be highly season dependent from what used to be a continuous year-round of plant-harvest-plant cycle done every 30-45 days, providing a steady income to seaweed farmers who are 90 percent women. The study recommends short-term measures and long-term strategies that include: (i) implementing strict quarantine procedures; (ii) transferring the farming of E. denticulatum and K. striatum to deeper waters (2-5 m) using longlines or raft method where practical; (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; (iv) promoting the farming of a variety of E. denticulatum called million-million; (v) improving the genetic stock with alternative local strains; (vi) promoting income-generating activities for farmers, such as value addition using harvested seaweed; (vii) developing multitrophic sustainable aquaculture by integrating seaweed aquaculture with other...