The Coral's Tiny Partners That Make Hormones to Beat the Heat
Corals look like rocks or plants, but they are animals — and they do not face the warming oceans alone. Living in and on every coral is a community of microscopic partners, a microbiome. Scientists have now found that one group of coral bacteria does far more than keep the coral company: when the water gets dangerously hot, the bacteria make steroid hormones the coral itself can no longer produce, helping its cells survive.
The study, from NYU Abu Dhabi and published in Nature Microbiology, looked at corals of the species Acropora pharaonis from the Arabian Gulf, including corals collected near Saadiyat Island. The Arabian Gulf is one of the hottest seas corals live in, which makes it a natural laboratory for studying heat stress.
When the coral's own supply runs low
Steroid hormones — the family that includes testosterone and progesterone — help regulate the immune system. When temperatures rise, corals lose some of their ability to produce these hormones, just when they need a strong immune response to cope with heat stress.
That is where the bacteria come in. The researchers found that Endozoicomonas, a group of bacteria found with corals all over the world, produces steroid hormones including testosterone and progesterone as temperatures rise. The hormones help the coral mount a stronger immune response to heat stress, increasing the survival of coral cells.
"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. "We found that their bacterial partners can compensate by producing these hormones themselves, allowing the coral to activate an immune response that helps its cells survive the heat."
Steroid hormone production is usually associated with complex organisms, and only a small number of bacteria — including some in the human gut — were previously known to make these molecules. Finding coral bacteria doing the same job reveals a previously unknown function of the coral microbiome.
More than neighbours
"These bacteria are doing much more than simply living alongside the coral," said Shady Amin, associate professor of biology at NYU Abu Dhabi and senior author of the study. "They are providing the coral with molecules it needs to regulate its immune response at a time when the coral itself is under significant stress."
The finding adds a new angle to coral conservation. Much conservation work — coral nurseries, restoration, assisted evolution — focuses on the coral animal itself. This study suggests the helpful microbes living with the coral could also matter for helping reefs cope as ocean temperatures continue to rise. It does not, on its own, save a reef: it points to a new direction for research, not a finished solution.
It is also a vivid example of a partnership that GCSE and A-level biology students meet again and again: two organisms, each supplying what the other lacks, surviving together in conditions neither could handle alone. In this case the help arrives in the form of a hormone, made by a bacterium, at exactly the moment the coral's own supply fails.
If your child is learning about ecosystems, symbiosis or the effects of climate change on living things, a first lesson in biology can start with a coral, its bacteria, and a hormone that makes the difference between coping and collapse. Book your first lesson
Sources:
- Mohamed, A. et al., "Steroid hormones produced by coral-associated Endozoicomonas influence coral immune response during thermal stress", Nature Microbiology (2026), DOI: 10.1038/s41564-026-02494-1, as reported 2 November 2026: https://phys.org/news/2026-11-reveals-coral-bacteria-corals-survive.html
London Tutors — post your tutoring request and we will match you with a verified tutor.