The impact of bleaching on disease susceptibility and defence in reef building corals

Most scientists agree that sea temperature increases due to global climate change have already caused mass mortality of corals throughout the tropics over the last 5-10 years. Given the current climate change predictions from organisations like the Hadley Centre in the UK, it appears likely that increases in sea temperatures will cause the complete collapse of these ecosystems within only a few decades. These estimates may be too pessimistic, because corals are able to adapt to rising temperatures using a variety of mechanisms. However, at the same time coral diseases have become increasingly common, as they have in many other systems and groups of organisms. Several scientists have proposed that these increases in disease are linked to climate change and we aim here to test whether temperature stress increases a corals' susceptibility to disease by monitoring indicators of health, antimicrobial defences and bacterial community structure and function. There are other possible causes of the recorded increase in diseases, however, such as increased transport and transfer of micro-organisms via tourists or ships' ballast water, for example. It is therfore vital that we understand the disease process so that appropriate and effective measures can be used to improve the health of coral reefs.