GITA ROSHNI NARAYAN, HILDEGARD WESTPHAL
Leibniz Center for Tropical Marine Ecology (ZMT), Biogeochemistry & Geology, Germany
Tropical reefs provide a number of important ecosystem services and a resource base for generating fisheries income and act as the food source for island coastal communities. Reef ecosystems in Zanzibar for instance, are currently threatened by local anthropogenic disturbances including: untreated, urban wastewater pollution; increased boating activities; overharvesting of marine resources and the effects of future predicted climate-driven ocean warming. These factors and especially high nutrients and climate"=driven warming are deleterious to benthic, marine calcifiers such as corals and large benthic foraminifers (LBFs). Both corals and LBFs possess algal"=symbionts, however stressors such as oceanic warming increase mortality, resulting in the expulsion of symbionts and subsequent bleaching. Increased atmospheric CO leads to acidification and a decrease in abundance and richness of species. Large benthic foraminifera (LBFs) are found in high abundance and taxonomic diversity in reefs world-wide. In the past decade they have been increasingly used as a tool for monitoring water quality and in quantifying reef health. Unlike corals, their high sensitivity and fast reproduction results in a fast response to environmental changes. Therefore, LBFs provide a rapid, cost"=effective way to assess reef"=scale changes crucial for future ecological forecasts due to human disturbance, eutrophication, warming temperatures and ocean acidification. In Zanzibar's reefs, LBFs are prolific calcium carbonate (CaCO3) producers contributing to the carbonate budget and stability of reefs. The comparison between communities from impacted and non"=impacted reefs shows warning signs of degradation due to local impacts. Long term monitoring is crucial in securing the economic welfare of Zanzibar's reefs.
Keywords: Eutrophication, fisheries income, large benthic foraminifers, ocean acidification, overharvesting, tropical reef ecosystems, urban wastewater pollution, Zanzibar