Msafiri A. Ndawala1, Flower E. Msuya2 ,Amelia S. Buriyo2, Ester Mvungi2
1Tanzania Fisheries Research Institute, United Republic of Tanzania
2Botany Department, University of Dar es Salaam, United Republic of Tanzania.
Euchematoid seaweeds namely Kappaphycus alvarezii and Eucheuma denticulatum are widely cultivated in marine water of Tanzania especially in Zanzibar Island. But recently due to climate change which resulted into change in environmental parameters especially increase in seawater temperature and salinity, diseases prevalence in seaweed has increased which lead to decline in seaweed production in the country. Therefore this study intended to assess the seasonal variation seaweed diseases prevalence, growth and carrageenan properties of two farmed seaweed, Kappaphycus alvarezii and Eucheuma denticulatum in Unguja Island, Zanzibar, Tanzania.
Present study show that the prevalence (%) of seaweed diseases was significant higher low during cold season than in hot season, Kappaphycus alvarezii diseases prevalence mean value were 34.0±2.14 and 44.0±2.1, t(14)=-5.80, P<0.05 while in Eucheuma denticulatum diseases prevalence mean value were 19.33±8.0 and 29.3±2.1, t(14) =-3.50, P<0.05 respectively. However seaweed growth rate (% increase in fresh weight day-1) was significant higher in cold season than in hot season. Kappaphycus mean growth rate values were 3.29±0.06 and 1.57±0.41, F (1) =16.42, P<0.05 while Eucheuma mean values were 3.05±0.35 and 2.77±0.44, F (1) =24.28, P<0.05. (P<0.05) respectively. Carrageenan yield (%) and gel strength (g cm2) of seaweed Kappaphycus were significant higher in cold season which had a mean value of 52.33±0.961% and 310.38±15.82 than in hot season which had a mean value of 33.36±1.37% and 218±5.31, P<0.05. Similarly in Eucheuma whereby in cold season carrageenan yield and gel strength were significant higher with a mean value of 43.82±0.29% and 209±3.41 than in hot season which had a mean value of 36.07±0.79% and 178.92±2.42, P<0.05 respectively.
It is therefore concluded that in order to obtain maximum sustainable yield from seaweed farming, farmers should concentrate on farming during cold season and shift to other activities during hot season. Alternatively, farmers should use biosecurity practices as it has evidently proven to be among of the best mitigate measure in seaweed diseases prevalence. Moreover, the study provides significantly information which contributes to the scientific efforts aiming at sustaining the seaweed industry in Tanzania.
Keywords: Biosecurity practices, carrageenan properties, growth rate, Seaweed, diseases prevalence.