In the SE Persian/Arabian Gulf, a small basin with weak connection to the main Indo-Pacific reef-belt and, reef decline was observed that can be clearly linked to climate change. Two heat anomalies in 1996/8 caused coral mass mortality but apparently surviving corals had higher heat-tolerance since bleaching in 2002 and 2007 resulted in only minor coral death. Corals had the highest bleaching thresholds in the world. However, a triple bleaching event (2010/11/12) led to disease outbreaks comparable to those known from the Caribbean and to comparable coral losses. The two ocean basins now share similar degradation dynamics – first Acropora populations were reduced to ecological insignificance, and then diseases massacred the Porites harrisoni complex, the ecological equivalent of the Montastraea annularis complex in the Caribbean. In the Gulf, diseases killed corals that might otherwise have demonstrated a reef system’s capability to adapt to climate change. The Gulf’s shift into a warm-phase suggests that continuing stresses will likely only allow persistence of a highly degraded system. This represents a disruption of a community pattern that exists since the Pleistocene.