With the oceans becoming warmer and more acidic, the world's coral reefs are confronted with increasing danger of heat stress and severe bleaching, as we've seen with Australia's Great Barrier Reef in recent years. Scientists are taking inspiration from recent advances in human microbiome research to investigate how transplantations of helpful bacteria can help increase heat tolerance in vulnerable species, with some promising early results.
So grave is the threat to the world's coral reefs that scientists are exploring all kinds of possibilities when it comes to ensuring their long-term survival. These include protective films to block harsh sunlight, underwater speakers that lure in fish to restore reef structures, and raising turbo-charged coral babies in huge floating nurseries.
The international team of researchers behind this latest study, led by scientists at the GEOMAR Helmholtz Centre for Ocean Research Kiel, set out to explore how a microbiome transplantation could offer susceptible corals a helping hand.
Study of the microbiome in humans has gained momentum in recent years on the back of fascinating findings around how gut bacteria can shape all sorts of health outcomes, ranging from improved blood pressure to Alzheimer's. In humans, scientists have found some success in altering a person's microbiome through fecal transplants sourced from healthy subjects, and the authors of this new study wondered whether corals might benefit from a similar approach.
"The idea is that probiotic bacteria with beneficial functions could help a coral to better withstand heat stress," explains Dr Anna Roik from GEOMAR, lead author of the study. “In the current study, we tested the approach of a 'microbiome transplantation', inspired by microbiome-based applications we know for example from clinical treatments."
For their experiments, the scientists used reef-building coral species from Thailand called Pocillopora and Porites. The team identified heat-tolerant "donor" corals in the wild along with vulnerable recipient corals, and then transplanted material between the two to modify the bacterial microbiome.
“We then used material from the coral tissue of the donor corals to inoculate conspecific, heat-sensitive recipients and then documented their bleaching responses and microbiome changes using a genetic analysis method called 16S rRNA gene metabarcoding,” explains Dr Roik.
This showed that the recipient corals, from both species, bleached more mildly than a control group during short-term heat stress tests, where they were subjected to balmy water temperatures of 34 °C (93.2 °F).
"The results show that the inoculated corals were able to resist the heat stress response for a short time,” explains study co-author Dr Ute Hentschel Humeida.
This isn't the first time we've looked at how helpful bacteria could be used to boost the chances of survival for vulnerable corals. Last year, an international team of scientists published research detailing how coral could be given probiotics to make them more resilient to stress, in a process likened to feeding them a scoop of probiotic yoghurt.
Microbiome transplantations represent another interesting pathway forward for researchers in the field. While scaling up these techniques to address dying coral around the world would be a massive task, studies like this add to our knowledge around coral health, and may feed into a patchwork of conservation strategies to ensure their long-term survival.
The research was published in the journal Microbiome.
