Coral species diversity in relation to geographic location- Seminar Paper

For millions of years, a diverse and abundant bacterial relationship has existed with corals. These bacteria can inhabit a range of niches within the corals; however the variation of bacteria between different coral species and their functional role in relation to the host is still waiting to be understood. The idea of mutualistic benefits between bacteria and the host, from processes such as fixation, has been suggest as a reason for this symbiosis. Microbial communities play an important part in coral symbiosis, and have been shown to have the ability to exclude undesirable bacteria by the production of antibiotics environmental changes are resulting in changes in bacterial community dynamics, however the effect of this shift on coral health is unknown. Therefore knowledge of bacterial communities associated with reef-building coral, aids understanding of multispecies mutualism and helps identify which species play a key role in maintaining coral health.

It is thought that bacterial groups may vary between coral species, but evidence has suggested that coral species in different geographic reefs will harbour the same bacterial communities. The aim of this study was to examine coral-associated communities to test assumptions about specificity in coral bacterial associations. Bacterial profiles of three species of Acropora (A.millepora, A. Tenuis, A.valida) from two locations, Magnetic and Orpheus Island, on the Great Barrier Reef, were used to determine whether genetically similar corals differ in structure of bacterial communities. Data collected from the two locations was compared to identify which bacteria were conserved across the geographically distinct locations. An additional study was carried out on A. millepora samples from Orpheus Island to see whether temporal environmental changes would lead to natural variation in coral bacterial communities. The analysis of samples was done using three culture independent 16s rRNA gene profiling methods: clone library construction, DGGE and TRFLP.

DGGE and TRFLP profiles were found to differ between corals from the different reefs, whereas non-metric multidimensional scaling of TRFLP data showed that the samples were grouped according to location rather than coral species. Overall the results indicated that certain bacterial groups associated specifically with corals, but dominant bacterial genera differed between geographically spaced corals. For the additional samples of A. millepora collected, bacterial communities were found to be consistent throughout the year; indicting a stable community despite temporal changes.

A theory proposed for the variation in dominant members of the microbial community in different locations, was the coral probiotic hypothesis: that corals potentially adapt to new environmental conditions by altering species specific symbiotic bacterial partners. This hypothesis seems to make a lot of sense due to evolution; if an organism wants to survive it must adapt to survive in a specific niche. This theory is also backed up by the authors mention that the reefs at Magnetic Island were more coastal and therefore subjected to greater seasonal sea temperature variation, sedimentation and nutrients. Further research should be carried out testing different environmental factors on the bacterial community composition to see how they are affected.