Near Saadiyat Island in Abu Dhabi, coral bacteria may be doing more than sharing a home with their host: as the water heats up, they can make hormones that help coral cells survive.
The finding comes from a study by researchers at NYU Abu Dhabi, published in Nature Microbiology. It offers a closer look at how corals and their microscopic partners respond to heat stress, a growing concern as ocean temperatures rise. The researchers say the results could help guide future reef conservation, though they do not describe a ready-to-use treatment.
The team studied Acropora pharaonis corals from the Arabian Gulf, including corals collected near Saadiyat Island. They found that Endozoicomonas, a group of bacteria commonly associated with corals around the world, produces steroid hormones when temperatures rise. The hormones include testosterone and progesterone. In the study, these molecules helped corals mount a stronger immune response to heat stress and increased the survival of coral cells.
That bacterial contribution matters because heat can weaken the coral’s own hormone production. “When temperatures become high, corals lose some of their ability to produce steroid hormones that are important for regulating their immune system,” said Amin Mohamed, a research associate at NYU Abu Dhabi and the study’s first author. He said the bacteria can make up for that loss, helping the coral activate an immune response that supports cell survival.
Steroid hormones are usually linked with complex organisms. Only a limited number of bacteria have previously been shown to produce them, including some bacteria in the human gut. The discovery that coral-associated microbes can supply such molecules to their host adds a new role to the coral microbiome—the community of tiny organisms living with the coral.
“These bacteria are doing much more than simply living alongside the coral,” said Shady Amin, an NYU Abu Dhabi associate professor of biology and the study’s senior author. The research was carried out through the university’s Center for Genomics and Systems Biology, in collaboration with John Burt and the Marine Microbiomics Lab.
The work points to a possible shift in how scientists think about reef protection. Coral nurseries, restoration projects and assisted evolution focus mainly on the coral itself. This study suggests that beneficial microbes may also be part of the picture, by providing functions that help corals cope with harsh conditions. It does not establish that adding bacteria to reefs would protect them, but it gives researchers a specific relationship to investigate further.
With marine heat stress continuing to challenge reefs, the next step is to understand how these bacteria and their hormones work across coral species and real-world conditions. For now, the study shows that a coral’s ability to withstand heat may depend not only on the animal, but also on the microscopic partners living alongside it.