What is the coral microbiome?

Healthy digestion and a strong immune system might not be possible without the support of plentiful microbiomes living inside and outside us humans. Did you know that corals also rely on microbiomes to thrive?

Coral is alive!

Coral polyps, appearing like hands with many fingers reaching toward the water's surface. — Coral polyps. UF/IFAS Photo by Tyler Jones.

It is easy for me to forget that corals are animals. I grew up going to the beach, and I favored basking on the sand over swimming for most trips. As a child, I would scour the shore for perfect shells and pretty sea glass to decorate my sandcastles. Too often, I would come across pieces of hard, white, lifeless corals. With such qualities, I would almost equate them to rocks. Although considering their unique structures and seemingly porous textures, I also imagined them like walls for the homes of sea creatures. They are actually animals, and they are also underwater homes. Without the proper environmental conditions and a healthy microbiome, corals can die, and the sea creatures who need them for shelter will also feel negative impacts.

Benefits of the Coral Microbiome

Many microorganisms make up the microbiome of stony coral, including bacteria and microalgae. Bacteria, living in and on coral, help coral take in and process nutrients. Bacteria also act as a line of defense against harmful microbes that cause disease. Corals can’t fight these diseases on their own, so bacteria do the job in exchange for resources like food and lodging. Microalgae help coral for the same reasons. They live inside coral to get sustenance in the form of sunlight. When microalgae perform photosynthesis, the corals benefit from their production of oxygen and sugars. Additionally, the presence and activities of microalgae give corals their vibrant colors.

Poor or changing environmental conditions, such as water temperatures that are too high or too low, can affect corals’ abilities to keep their microbiomes teeming. Without these mutually beneficial relationships, corals can have poor health or die, impacting the sea creatures who use them for protection.

An EDIS publication, “The Coral Holobiont: A Brief Overview of Coral and Their Microbiome,” discusses all of this and more related to the roles of bacteria and microalgae in the coral microbiome. The authors define the coral microbiome and explain other influences on the health of a coral’s microbiome, as well as how certain factors can lead to coral death. To read more, find this publication on Ask IFAS at https://edis.ifas.ufl.edu/publication/SS733.

Learn More

Go to Ask IFAS to read more about other topics related to stony corals. For example, see this publication about artificial reefs as a solution to dying coral reefs: https://edis.ifas.ufl.edu/publication/FR450.

Also, further understand how environmental changes can affect corals by visiting blogs like this one at https://blogs.ifas.ufl.edu/miamidadeco/2025/01/10/extreme-cold-and-what-it-means-in-the-marine-world.