Calcium Carbonate Production, Coral Cover and Diversity along a Distance Gradient from Stone Town: A Case Study from Zanzibar, Tanzania

Coral reefs near Stone Town, Zanzibar, exhibit significantly lower calcium carbonate production (8.47 ± 4.37 kg CaCO₃ m⁻² yr⁻¹), coral cover (52.4 ± 13.9%), and biodiversity compared to those farther away or within marine protected areas, where values peak at 16.90 ± 9.70 kg CaCO₃ m⁻² yr⁻¹, 67.4 ± 8.7% cover, and higher diversity (H′ = 1.74 ± 0.20). This gradient suggests that human activities—such as fishing pressure, pollution, unregulated tourism, and anchoring—severely degrade reef health, while protection measures mitigate these impacts. The study highlights the critical role of distance from urban centers and management regimes in shaping coral community structure, with reefs closest to Stone Town dominated by stress-tolerant species like Porites lobata and P. rus. These findings underscore the need for targeted conservation efforts to preserve Zanzibar’s reef ecosystems.

Herrán, N., Narayan, G. R., Reymond, C. E., & Westphal, H. (2017). Calcium Carbonate Production, Coral Cover and Diversity along a Distance Gradient from Stone Town: A Case Study from Zanzibar, Tanzania. Frontiers in Marine Science, 4. https://doi.org/10.3389/fmars.2017.00412