Are Coral Reefs Doomed?

Probiotics to the rescue!

Would you like to swim in the midst of scintillating fish in coral reefs? Would your kids? The future is bleak for diving fans, with the ever-increasing bleaching of these gorgeous ecosystems.

Despite the dark situation, there’s hope to save the corals. Coming from bacteria.

Indeed, other organisms beyond algae associate to the coral’s holobiont, contributing to its biology — in particular, to stress tolerance and adaptability, more specifically through nitrogen fixation, sulfur cycling, scavenging reactive oxygen species (ROS), antibiotic production...

The scientists simulated a heatwave by exposing corals in aquariums to heat, with the highest point reaching 86°CF/30°C for 10 days, and they sprayed aquariums with either a control saline solution or Beneficial Microorganisms for Corals (BMCs), namely with a consortium coming from the natural reef’s ecosystem. The BMCs selected were an association of Bacillus lehensis, Bacillus oshimensis, Brachybacterium conglomeratum, Planococcus rifietoensis, and Salinivibrio sp.

These bacteria were selected based on the absence of antagonist activity against other selected BMCs, and no previous record of being harmful to humans or other marine life. Beneficial traits included nitrogen fixation, denitrification, dimethylsulfoniopropionate degradation, ROS scavenging potential, and antagonistic activity against two coral pathogens, Vibrio coralliilyticus, and Vibrio alginolyticus.

After the challenge, the stressed control corals expressed a 40% mortality, while the corals exposed to the beneficial bacteria consortium all survived. They were much quicker to recover their photosynthetic efficiency.

Stressed corals seem to have a quicker uptake of bacteria from their environment. When they are weakened by the heat and absence of their algal symbionts, it appears crucial to bring on board good bacteria, which will occupy the niche and create a barrier effect, protective against the colonization by pathogens — quite similar to what happens in humans. But there’s much more to it.

Transcriptomics, the science that reveals how genetic expression changes in response to their environment, showed reprogramming in over 2000 groups of genes with pronounced differences between the control and probiotic-treated group. It was possible to identify that the short-term genetic responses involved immunity, inflammation, apoptosis (the process of programmed cell death), and cellular reconstruction, among others.

This splendidly confirmed the usefulness of the probiotic approach to sustaining coral reefs.

Interestingly, the BMCs appeared to influence the overall composition of the coral’s microbial community, although at T3 the probiotics delivered were no longer discernable.

While it is easy to spray bacteria in a tank, it is much more difficult to do so in the vastness of the oceans. According to Raja Dhir, co-founder of Seed Health, a probiotic company partnering with the research project, even depositing the bacteria directly on the surface of the corals gives them very little probability of attaching.

One option explored by Raja Dhir and Raquel Peixoto is to deliver the bacteria through a sort of patch coated with a gel-like material that mimics the coral mucous layer and could help bacterial transfer. The team also evaluates the feasibility of using robots to cover more coral reefs more quickly, in this race against time.

The coral problem is not solved yet, and our responsibility and first action should of course remain to mitigate climate change, but we can also start to address the downstream effects of our human activities.

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