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Coral bleaching due to rising sea temperatures has become an increasingly prevalent threat, with the barren and colorless remnants of destroyed coral reefs observed globally. However, a study led by the GEOMAR Helmholtz Centre for Ocean Research Kiel has revealed the promising potential for microbiome targeting to be implemented as a method of coral heat stress protection.
World Ocean Day, founded in 1992, has become an annual event to celebrate and raise awareness of the crucial role our oceans play. Corals are recognized as an integral part of our marine ecosystem, providing a home to a multitude of species, protecting our coastline from the impact of tidal power, and responsible for over 50% of global oxygen production. Scientists are desperate to combat the devastating effects of coral heat stress if we are to maintain ecological harmony.
The recent study, published in the International Journal Microbiome, has demonstrated the implementation of bacterial transplantation to achieve increased short-term heat resistance in two species of heat-sensitive corals.
Why are Coral Reef Systems Endangered?
Corals are an integral part of tropical marine ecosystems. Home to 25% of all ocean fish and providing a vital habitat for algae which produce 50% of Earth’s oxygen, coral reefs have been granted the title of “rainforests of the sea”. They are also responsible for absorbing 97% of tidal energy, protecting coastal communities from the most devastating impacts.
These backbones of our planet are however under increasing threat from the effects of global warming. As the ocean temperatures continue to rise, coral bleaching continues to increase as a result of the disruption to the symbiosis between the coral and its residing dinoflagellate symbionts. 2016 saw the first mass coral bleaching recorded in the Far-Northern Great Barrier Reef; 85% of the area was encompassed by thermal affliction. As this continues to rise, our coral reefs are now on a trajectory to ecological collapse if immediate action is not taken.
Rising Ocean Temperatures are "Cooking" Coral Reefs | National Geographic
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What is Microbiome-Targeting?
The term microbiome refers to the collective genomes of all micro-organisms living in a unique habitat. Within the human body, this microscopic framework has such a crucial role in supporting our bodily functions that the human microbiome is defined as its own supporting organ, and as such constitutes a huge area of continuing research.
A treatment that has evolved from this is fecal microbiota transplantation. Our gut is a haven of diverse microbes and its careful composition must be maintained for our gut to function smoothly. For those who find this harmony is not maintained, the transplantation treatment involves the transfer of healthy bacteria from a donor into the intestines of the patient to restore the bacterial balance.
However, it is important to note that the microbiome is not solely a supporting organ of humans. All habitats, living organisms, soils, and oceans among many, will have their own unique microbial network. Hence, the team at GEOMAR has identified the opportunity to apply this well-practiced method of microbiome transplantation to the protection of our coral reefs.
How Can Microbiome-Targeting Aid Coral Conservation?
A research group, led by the GEOMAR Helmholtz Centre, has begun a promising investigation into the application of microbiome transplantation to increase the heat stress resistance of coral. As summarised by Dr Anna Roik, lead author of the published study, “The idea is that probiotic bacteria with beneficial functions could help a coral to better withstand heat stress.”
With funding from Kiel University, as part of a wider Future Ocean Network project, the team conducted experiments on two heat-sensitive reef-building corals, Pocillopora and Porites, found in the Andaman Sea of Thailand.
Heat-resistant donor corals were identified and hence utilized as bacterial donors to inoculate the two test species. These were subsequently subjected to a short-term heat stress test, conducted at 34°, throughout which the corals’ bleaching and microbial responses were recorded through the genetic analysis method, 16S rRNA gene metabarcoding.
Although only an initial investigation, the results obtained are certainly promising. Both recipient corals displayed decreased bleaching compared to the control group, providing evidence for microbiome inoculation as a viable method to improve short-term coral heat sensitivity. Detection of the donor bacteria on the host corals also revealed that putative bacterial symbionts constituted the majority of the bacteria successfully transmitted, indicating that corals may favor this particular species. This observation will greatly aid the success of further studies, offering the potential to achieve greater temperature resistivity if bacterial uptake can be optimized.
Continued Research into Coral Conservation
The published study clearly highlights coral microbiome targeting (CMT) as a promising pathway towards reducing coral heat sensitivity. However, it is important to note that this method currently remains in its infancy stage, limited to the consideration of short-term effects.
As such, Dr Roik explains: “further experimental studies are required to unravel the exact mechanism of action, as well as long-term field-based studies to test the durability of the effect", outlining the crucial next steps to the project.
The feasibility of applying such a method to wide-scale coral protection is yet to be determined. The current process of transplantation could certainly be described as a tedious process, and considering coral reefs are estimated to cover 284,300 km2, it does lead to reservations regarding its global application.
The team does, however, recognize this as a potential barrier and propose an alternative avenue to the application of the results: “If scaling up the method will not turn out to be feasible any soon, another perspective is that CMT can serve as an elegant manipulative tool which could help further advance the identification of probiotic bacterial species and strains, which then could be further developed into a probiotic inoculation treatment.”
The study carries great significance for the continued development of probiotic treatment, and the results of further investigation will be awaited to reveal its feasibility in widescale coral conservation. Regardless of the latter outcome, it is important to commend the increased awareness that this will bring to the protection of our marine environment, a key aim behind World Ocean Day.
Announcing UN World Oceans Day 2021
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References and Further Reading
Coral Reef Alliance. (n.d.) Where are Coral Reefs Located? [online] Saving the World’s Coral reefs. Available at: https://coral.org/coral-reefs-101/coral-reef-ecology/geography/ (Accessed 12 May 2021)
Doering, T., Wall, M., Putchim, L. et al.. (2021) Towards enhancing coral heat tolerance: a “microbiome transplantation” treatment using inoculations of homogenized coral tissues. Microbiome 9, (102). https://doi.org/10.1186/s40168-021-01053-6
Gupta, S., Allen-Vercoe, E., & Petrof, E. O. (2016). Fecal microbiota transplantation: in perspective. Therapeutic advances in gastroenterology, 9(2), 229–239. https://doi.org/10.1177/1756283X15607414
Harvard School of Public Health. (n.d.) The Microbiome. The Nutrition Source. Available at: https://www.hsph.harvard.edu/nutritionsource/microbiome/ (Accessed 11 May 2021)
Marchesi, R. (2017) What is a Microbiome? [online] Microbiology Society. Available at: https://microbiologysociety.org/blog/what-is-a-microbiome.html (Accessed 11 May 2021)
NOAA Office for Coastal Management. (n.d.) Coral reefs. [online] NOAA Office for Coastal Management. Available at: https://coast.noaa.gov/states/fast-facts/coral-reefs.html (Accessed 13 May 2021)
Science Daily. (2021) Protecting coral from heat stress and coral bleaching. [online] Science Daily. Available at: https://www.sciencedaily.com/releases/2021/05/210507112016.htm (Accessed 11 May 2021)
Thruthout. (2017) Coral Reefs Could All Die Off by 2050. [online] EcoWatch. Available at: https://www.ecowatch.com/coral-reef-bleaching-2408656490-2408656490.html. (Accessed 11 May 2021)
UNESCO. (n.d.) World Oceans Day. [online] UNESCO. Available at: https://en.unesco.org/commemorations/oceansday. (Accessed 13 May 2021)