The 1997/1998 Mass Mortality of Corals: Effects on Fish Communities on a Tanzanian Coral Reef

The abnormally high surface temperatures in the worldʹs oceans during 1997/1998 resulted in widespread coral bleaching and subsequent coral mortality. An experiment was performed to study the effects of this coral mortality as well as the influence of the structural complexity on fish communities on a Tanzanian coral reef. Changes in fish communities were investigated on plots of transplanted corals after 88% of these corals had died. A distinct shift in fish community composition was found, although diversity was not affected. Fish abundance rose by 39% mostly due to an increase in herbivores, which seemed to benefit from enhanced algal growth on the dead corals. Fish abundance, species diversity and community composition were also strongly influenced by the structural complexity provided by the live and dead corals. This suggests that a coral reef can support abundant and diverse fish populations also after the corals have died as long as the reef structure is sustained.