Microbes Could Be The Key To Coral Death

"Many 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," says Dr John Bythell, a biologist from Newcastle University. "These microbes can be thought of as being similar to the bacteria that normally live in our guts and help us digest our food."

Changes in sea temperature caused by climate change and global warming affect corals, but they also affect the types of bacteria and other microflora that live with them. When the water warms up, some disease-causing bacteria are more successful and can attack the corals. The corals themselves suffer from heat, which reduces their defences. Also, some of the friendly bacteria that normally live in the corals' guts become weakened, allowing other harmful bacteria to multiply and cause diseases or other problems.

Defensive mucus
A key factor newly identified by the Newcastle team is the role of surface mucus secreted by corals. This seems to act as a shield, preventing disease-causing pathogens such as bacteria and some viruses from penetrating their 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.

"If we want to protect and conserve these reefs for the future, we need to start acting now. And before we can do that we need a better understanding of the processes," says Dr John Bythell. "The mass mortality of two of the dominant coral species in the Caribbean due to disease has been unprecedented in the last 3,000 years, which suggests a strong link to man-made activities."