Substantial impacts on community structure have been observed in coral reefs during periods of warmer than normal sea temperatures. Poised near their upper thermal limits, coral reefs have undergone global mass bleaching events whenever sea temperatures have exceeded long-term summer averages by more than 1.0 [degrees]C for several weeks [41, 47]. Six periods of mass coral bleaching have occurred since 1979 and the incidence of mass coral bleaching is increasing in both frequency and intensity [41]. The most severe period occurred in 1998, in which an estimated 16% of the world's reef-building corals died [48]. The impact of thermal stress on reefs can be dramatic, with the almost total removal of corals in some instances [41, 49, 50, 51]. In some cases (usually smaller or shorter thermal anomalies), thin-tissued, branching acroporid and pocilloporid corals have bleached and/or died preferentially, leaving more massive species like Porites spp intact. In other cases, all coral species have been largely removed [51, 52]. Estimates of how ecosystem species richness and community structure have changed after bleaching events are generally unavailable, but such changes are suspected to be large.