The threat of coral bleaching on a global scale is a growing concern both because of the reduction in essential ecological services provided by zooxanthellae (symbiotic algae) containing corals within reef communities, and the potentially devastating economic impacts of their demise. Coral bleaching is the largest natural cause of coral death. During the 1997-1998 El Niño-Southern Oscillation (ENSO), 16% of the world's coral reefs died.
we are currently studying the response of coral tissue under thermal stress, and have found that the coral goes through programmed cell death (PCD). Interestingly, some corals, which proved to be resilient to thermal stress, are capable of biochemically inhibiting PCD (Kvitt et al 2011, Tchernov et al 2011).
The coevolution (if indeed a reciprocal evolutionary change in interacting species has occurred) of scleractinian corals and zooxanthellae started as early as the Norian period (A sub-division of the late Triassic period, from 220.7 to 209.6 Ma.), however, very little is known about the evolutionary mechanism that led to the formation of this symbiosis and to the conditions that maintained it for such a long period. This leads to major questions, such as 1) Perhaps coral bleaching is just a selective mechanism that is an integral part of algae-coral coevolution? And 2) On the other hand, coral bleaching might be a consequence of the latest climatic changes brought about by anthropogenic activity?