Distribution and abundance of diseases on reef corals in Tanzania

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University of Dar es Salaam
Diseases affecting reef corals are on the rise in the world oceans. Warming of the seas, deteriorating water quality and increased human activities in the nearshore waters are considered to play a major role in the prevalence of coral diseases. The goal of this study was therefore to characterize and investigate the abundance of coral diseases and its environmental drivers in reefs off Zanzibar and the main coast of Tanzania. To achieve these, 20 sites were selected along the whole coast of Tanzania and nearby islands. Rapid assessment surveys, line intercept transects and belt transects were used to monitor the selected study sites. In addition, the effect of temperature and nutrients on white syndrome (WS) disease on table Acropora and bleaching on Porites australiencis was assessed through sets of experiments done both in laboratory and in the field. The study has revealed seven coral diseases with significant difference between localities (p < 0.001). The mean prevalence was relatively low ranging from 2.24±1.6% in Pemba to 0.09± 0.3% in Zanzibar Stone town reefs. Prevalence of WS on table Acroporids was significantly higher during warm season 5.63±3.7 than cool season 3.55±2.2% (p<0.05). The progression rate was higher (p<0.05) during cool period where 80.42±15.42 cm2/day was recorded compared to 16.14±8.79 cm2/day recorded during warm period. These results show that there is no relationship between temperature and WS prevalence but the virulence of WS is more pronounced during cool season. When temperature and nutrients were manipulated over bleached Porites australiensis to check the progression rate of bleaching over time scale, the bleached corals did not show any significant difference between the treatments. Similarly, the treatments could not result in bleaching on healthy corals. These results show that temperature and nutrients at the levels used in this study may not have direct impact on corals but may delay coral recovery from any unforeseen impact. Disease prevalence in Tanzania water is low compared to other regions in the world. Low prevalence may be due to low levels of anthropogenic influence as compared to the areas with higher disease prevalence. Coral bleaching is the major threat to coral reefs as when it occur it cover large geographical area and involves many coral species.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THF EAF QL377.C5T34M63)
Corals, Diseases, Tanzania
Mohammed, M. S. (2016) Distribution and abundance of diseases on reef corals in Tanzania, University of Dar es Salaam, Dar es Salaam.Doctoral dissertation,