Microbiota shifts in the mucus layer of corals

The surface mucopolysaccharide layer (SML) of coral harbours a diverse community of microbiota that is crucial to the health of the coral. This community provides a wide range of functions such as biochemical cycling and antibacterial production. Corals, however, experience SML microbiota shifts as they are moved to laboratory aquaria and this may be a confounding variable in many studies of coral-associated bacterial communities. Such shifts result in less diverse SML microbial communities compared to in situ coral SML samples. Pratte et al. (2014) set to investigate the temporal dynamics of these shifts.

Coral fragments from five scleractinian coral were collected from the Florida Keys National Marine Sanctuary Coral Nursery. Automated ribosomal intergenic spacer analysis (ARISA) was used to investigate the dynamics of the SML microbiota shift of the coral Siderastrea siderea after transfer from a natural environment to aquaria.

Samples from the initial SML bacterial communities and those collected one day after transfer were the most diverse compared to samples from days 7,14 and 28. Initial SML bacterial community samples and those one day after transfer clustered independently from each other and all other samples. This indicates a substantial shift in the SML community after transfer. One week after transfer the SML bacteria showed tighter clustering indicating more similar communities. The SML bacterial communities began to stabilise 7-14 days after transfer. Despite this stabilisation, the initial and final communities were very different. There are many possible reasons for this shift such as a change in available nutrients or disruption of microbial interactions. Another possible explanation is that this shift reflects the coral’s inability to maintain the pre-existing SML community due to stress. This could be further detrimental to the coral if beneficial bacteria are lost. The authors attempted to identify the bacterial community members via clone libraries but GenBank did not contain matches for the majority of the clones sequence suggesting that coral bacterial studies should target the 16S rRNA gene.

This is the first study to examine the temporal dynamics of the shift in coral SML microbiota when host corals are transferred from the reef to aquaria. The results from this study that there might be limited learning potential from lab based experiments if bacterial communities are very dissimilar to natural populations. The use of more in situ studies may be beneficial but would also incur extra costs. If lab experiments are used then they should be left to stabilise for at least 14 days in order to limit any false results from shifting communities. Further understanding of bacterial communities which make up the SML in both natural and lab conditions will help us to understand how these changes affect the coral. This could possibly be used to help limit differences between the two populations and their impact on the coral. This may allow lab experiments to be used with more confidence with results having more ecological significance.

Pratte, Z. A., Richardson, L. L., & Mills, D. K. (2015). Microbiota shifts in the surface mucopolysaccharide layer of corals transferred from natural to aquaria settings. Journal of invertebrate pathology, 125, 42-44

http://www.sciencedirect.com/science/article/pii/S0022201114001876