Global warming affecting coral microbes

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The litany of woe continues for coral reefs, with microbiologists now identifying a new threat to their survival " the bacteria that live on them.

Speaking at the 162nd meeting of the Society for General Microbiology, Dr John Bythell of Newcastle University identified the changing microbial flora living on corals (due to global warming) as being yet another agent of destruction of coral reefs.

According to Dr Bythell, any of the deaths we see in the coral reefs, which occur following coral bleaching events, when huge areas of reef die off like in 1998 when 17% of the world's reefs were killed, can be put down to changes in the microbes which live in and around the reefs.

Climate change and global warming result in changes to sea temperature, which in turn can change the composition of the bacteria and other microflora living on corals.

Increasing sea temperatures may cause some disease-causing bacteria to proliferate and weakens the defence mechanisms of the corals.

This leads to increased susceptibility to diseases, a process that may be bolstered by the fact that beneficial bacteria living in the corals' guts decline with increasing temperatures, allowing other harmful bacteria to take over and wreak havoc.

Dr. Bythell and his co-workers have also identified the surface mucus of corals as a key factor in reef health.

This mucus layer apparently acts as a barrier, preventing pathogens such as bacteria and some viruses from penetrating the corals' tissues.

The reefs' defensive mucus or slime is also at risk from stresses brought on by climate change. This seems to happen just at a time when some of the key functional microbe groups are changing, reducing the corals' other defences and boosting some disease-causing bacteria, making them more virulent, says Dr Bythell.

For more information on this subject, see the following studies:

Ritchie, KM (2006) Regulation of microbial populations by coral surface mucus and mucus-associated bacteria. Marine Ecology Progress Series 322, pp. 1"14.

Lesser, MP, JC Bythell, RD Gates, RW Johnstone and O Hoegh-Guldberg (2007) Are infectious diseases really killing corals? Alternative interpretations of the experimental and ecological data. Journal of Experimental Marine Biology and Ecology 346, pp. 36"44.