The cause of WBD is little understood but by using experimental antibiotic treatments the researchers behind this study have identified a number of pathogens potentially responsible for WBD in Acropora cervicornis, a reef building coral which is now critically endangered according to the ICUN Red List. By identifying causes of the disease scientists may be able to develop treatments to arrest the progress of WBD though the Caribbean reefs.
The team analysed samples of the coral with and without the disease to identify a line up of potential pathogens which were present in the diseased samples but absent in the healthy samples. In total 15 prokaryote (bacteria and archaea) and a diverse community of microorganisms called ciliates were identified.
The team soaked the samples in different antibiotic treatments which aimed to reduce the numbers of the different pathogens to undetectable levels. The antibiotics did not harm the healthy corals and some treatments were able to arrest the development of WBD. Other treatments effectively killed off certain bacteria but were unable to stop the spread of the WBD. This method helped the scientists eliminate some pathogens from their short list. In the end they had ruled out all but three of the potential primary WBD-causing bacteria pathogens.
The team also identified a micro-organism called a ciliate which is also likely to be involved in the disease. The researchers suggest that the bacterial pathogens cause cellular damage and large mobile populations of the ciliate, Philaster lucinda, consume the damaged coral tissue leaving its exposed skeleton.
‘These results highlight why researchers have struggled to find a single agent causing these 'White Syndromes' on coral reefs around the world. It’s likely that many coral diseases are caused by a mixture of micro-organisms and not by a single pathogen’ says Michael Sweet, the author of the study.
While more study is necessary, understanding the pathogens causing the disease may help scientists develop large scale antibiotic treatments in the future.