Coral reefs cover over 100,000 square miles of ocean floor across the globe and exert a widespread influence on both marine and human life. However, since the 1980s, scientists have observed mass loss of their bright coloration, called bleaching. This bleaching is a sign of starvation and has been linked to changing sea temperatures. Current estimates suggest that the world’s coral reefs could be lost entirely by the end of the millennium if no interventions are taken. While governments are attempting to curb global climate change through carbon emission and other policies, some scientists are hoping for a bioengineering approach from some of the smallest inhabitants of coral reefs – bacteria. Just as microbes support human health in the gut by breaking down food, some researchers believe that beneficial coral microbes can help protect their hosts against environmental stress.

Scientists at the GEOMAR Helmholtz Centre for Ocean Research tested this hypothesis by performing coral microbiome transplantation experiments with the reef-building corals Pocillopora and Porites in the Andaman Sea in Thailand. They took the bacteria from heat-resistant donor corals and transferred them into heat-sensitive recipient coral counterparts. Upon exposing the corals to heat stress, they observed their bleaching responses and sequenced their bacterial microbiome. The recipient corals of both species underwent lower levels of bleaching when inoculated with the donor coral bacteria, suggesting that uptake of beneficial bacteria protected the corals from heat-induced stress.

This type of microbial therapeutic presents an opportunity to administer a quick and affordable treatment directly to ailing corals in the wild, or to transplant new lab-bred corals onto dying reefs. Some scientists even see probiotics as having the potential to reverse previous damage. However, further studies are required to determine how these bacteria are providing heat response benefits to the coral, and whether these responses are durable over time. There is also concern that seeding reefs with bacteria may fundamentally alter the ocean ecosystem or cause other unintended coral diseases. While the most cautious road is to wait until we understand more, dire circumstances could potentially mandate an extreme approach.  

Dr. Anna Roik is a post-doctoral fellow at the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg in Germany. Talisa Doering is a Ph.D. candidate at the University of Melbourne.

Managing Correspondent: Lauren Davancaze

Press Articles: “Using probiotic bacteria to protect against coral bleaching,” Phys.org

Original Journal Article: “Towards enhancing coral heat tolerance: a ‘microbiome transplantation’ treatment using inoculations of homogenized coral tissues,” Microbiome

Image Credit: savethegreatbarrierreef.org