Reading through different coral scientific publication, we came across one, that could be quite relevant for us reef aquarist. In this publication published in Nature, scientist from the Red Sea Research center, from the King Abdullah University of Science and Technology (KAUST) in Saudia Arabia highlight the importance of microbial community in the adaptation of the coral to a different habitat.
Depending on the environment, bacterial community differs on the same coral species. The coral ‘holobiont’ together with its dinoflagellate association also harbor an important and particular community of bacteria, important for a whole range of biological functions like Nitrogen fixation, sulfur cycling, and protection against pathogenic bacteria.
Further, microbial diversity was shown to increase with depth in several coral species, possibly allowing corals to access a broader range of food sources. In addition, some studies have found seasonal fluctuations in coral-associated microbiomes and tide-related shifts on much shorter time scales, while other corals maintain temporally stable microbiomes.
This study try to elucidate whether coral microbiomes can recover from chronic pollution, i.e. return to a state that resembles conspecific microbiomes at unaffected sites upon transplantation of coral fragments from affected to pristine sites. Coral fragment were moved between pristine and human polluted damaged sites.
This finding would explain why some corals don’t do well when they are transplanted from a very healthy environment to a disturbed environment. It’s very helpful in restoration project but also would explain some of the problems we can encounter in aquaria, and the huge knowledge gap that need to be fulfilled. We know for a long time the importance of bacteria in reef tanks, but we still only have scratched the surface.
The combination of the coral host, the dinoflagellate associate that exist in many species and strains, plus the complex bacterial community would explain why 2 pieces of corals are different, even from the same species, and the same habitat. There is practically no such a thing of two identical corals. Each coral need to find a corresponding bacterial community depending on the particular environment. This will explain, why some coral go to a long vegetative stage before starting to grow again and color up.
An increase in bacterial diversity in coral microbiomes often accompanies the stress response as a result of emerging opportunistic taxa that are otherwise absent or suppressed. Also, increased bacterial diversity has been repeatedly observed in diseased coral microbiomes. Explaining why corals are more susceptible to disease in impacted sites, even though some non pathological bacteria were also present in higher numbers.
This would also explain why no two aquariums are the same. If empirical methodology was the main driver in our industry in the past, a lot of new science aquarium based technology keep coming up, and hopefully, with science based knowledge, it will help us understand these mechanism that in turn will help us save the reef.
Importantly, it has to be considered that corals are in general long-lived, sessile animals that are unable to escape changes in their environment. And because of their long generation times, evolutionary change is supposedly slow. Strategies to cope with and survive rapid environmental change are therefore critical.
One mechanism by which corals may adjust more rapidly to change may be through their association with different bacterial taxa, whereby selection occurs for the most advantageous and beneficial microbiome in a particular environment. This could help to answer why in mariculture, for example only a couple specimen of one species survive a stressful event, and all the other one die. Leading to another path to adaptation through the use of bacterial community.
Finally the last interesting conclusion, is that reducing and removing sources of pollution and sedimentation may result in the reversal of bacterial community. This finding holds the promise of microbiome recovery, encouraging the reduction of anthropogenic pollution, even in reef areas where coral assemblages are already degraded.