Institute of Marine Sciences, P.O. Box 668, Zanzibar, Tanzania

muhando@zims.udsm.ac.tz

The 1998 coral bleaching and mortality event was the most severe natural calamity ever recorded in Tanzania. The coral mortality was not uniform. In most areas, mortality was higher on the reef flat than on the reef slope and Acropora was the most affected coral group. The extent of mortality differed even between nearby reefs, e.g., while mortality around Tutia reef in Mafia was about 80%, it was less than 30% in Chole Bay, about 8 km north. Similarly, live coral cover decreased from 52 % in 1997 to 28 % in 1999 on Chumbe reef while it increased from 53 % in 1997 to 57 % in 1999 and from 45% to 53 % on Bawe and Pange reefs, respectively. High coral mortality was noticed on Misali reef in Pemba and on Tutia reef in Mafia and lowest mortality was observed on reefs around Zanzibar and Kunduchi, north of Dar-es-salaam. Three factors, seawater temperature, current system and size of shallow water area together appear to explain the discrepancy in the extent of observed mortality.

There were no obvious changes on the distribution and abundance of macrobenthos that could be associated with the coral bleaching and mortality event. The notorious coral eating starfish crown-of-thorn starfish was and is still present in low numbers on most coral reefs surveyed in 1997 and 1999. The abundance of invertebrates of commercial value, such as lobsters, sea cucumbers, octopus, and shelled molluscs was low due to over-exploitation even before the bleaching event. Reef fish composition has changed in favour of herbivorous fish (e.g., 39 % increase in Mafia) while the total numbers does not appear to have changed much. Macroalgae abundance have increased on some reefs, e.g., on Chumbe reef (8.8 % to 18.4 %), Kwale reef (16.6 to 26.2 %) and Tutia (1-15.4 %) and have remained low on reefs in Bawe, Changuu, Mnazi bay, Chole Bay, Dar-es-salaam and Misali reefs in Pemba.

The artisanal as well as commercial fisheries do not appear to have been affected by the bleaching event. Similarly, there are no specific complains from the tourism sector indicating that the tourism has been affected.

With the exception of Kwale reefs on the south west of Unguja, preliminary investigations indicate that coral recovery has started. The survived coral colonies are growing fast and new coral recruits are settling (0.1 - 4 m^-2 ). However, because of various reef-degrading activities carried out on Tanzania reefs, rapid recovery will depend on effective enforcement of existing legislation that protects reef environment and its resources. Research and monitoring as well as mitigation (restoration) measures are needed to guide the management of coral reef environment.