Publication Date

Spring 2018

Program Name

Tanzania-Zanzibar: Coastal Ecology and Natural Resource Management


Sedimentation is one of the greatest threats reefs face today due to climate changeinduced sea level rise. Mnemba Island has experienced rampant coastal erosion as a combined result of global processes and local anthropogenic impacts, which has in turn caused severe reef degradation. The house reef was surveyed over a 3-week period to determine the amount of sediment deposited on the reef and the impact of this sedimentation on coral reef health. Sediment traps were deployed to measure the sediment flux rate. The line-intercept transect method was used to measure the benthos cover of the reef and point-transect method was used to measure the relative sediment cover of the substrate. Counts of indicator fish species (Scaridae, Balistidae, and Siganidae) and echinoderm (Echinoidea and Acanthaster planci) species were counted using the belt transect method. Overall, the reef exhibited very poor health that calls for urgent attention. Sediment flux rates on the reef are close to the lethal limit, potentially impacting algal growth. The reef is comprised of a low percentage of live coral cover and few herbivorous fish species. Furthermore, much of the reef is overtaken by Echinoidea. These findings suggest that sedimentation is a primary cause of reef degradation in conjunction with significant and direct anthropogenic impacts. Current erosion mitigation practices are not sufficient to adequately protect the shoreline. Recommendations for urgent protection of the island and its reef are discussed.


African Studies | Environmental Health and Protection | Environmental Sciences | Environmental Studies


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