Ecological health of coral reefs in Zanzibar

Coral reefs are important ecosystems in terms of their biodiversity and ecosystem functions. Particularly at local scales, coral vulnerable to natural anthropogenic disturbances, leading the degradation reef health. Here, we employed two different methods monitor First, conducted line transect surveys record benthic community structure infer ecological Secondly, trace metal concentrations sediment samples a bioindicator sponge species, Haliclona fascigera, were compared among sites detect cryptic unknown sources pollution. The study area comprised six situated along coast Zanzibar’s main agglomeration, Stone Town, subject types disturbances conservation management schemes. Overall, health was found decrease with increasing proximity living hard cover being particularly low on closest which coincided greater fishing, tourism, pollution pressures. Reef assessments based analyses differed from surveys. All showed high levels arsenic cadmium contamination, some revealing concerning chromium, copper zinc. significantly between each other concentration for both sediments (p = 0.031, PERMANOVA) 0.001, PERMANOVA). Trace not correlated distance highlighting downstream effects industrial urban sewage even remote reefs. assessment be dependent survey method employed, is why recommend combination complementary methods.