Corals depend on their microbiomes to endure heat stress

A recent study led by Penn State University found that corals’ microbiomes (comprising a large array of viruses, bacteria, and fungi) play a fundamental role in the ability to withstand rising ocean temperatures. Scientists also identified several coral genes and photosymbionts residing within their tissues which may improve corals’ responses to heat stress.

“Prolonged exposure to heat can cause ‘bleaching’ in which photosymbionts (symbiotic algae) are jettisoned from the coral animal, causing the animal to die,” said study co-author Monica Medina, a professor of Biology at Penn State. 

“We found that when some corals become heat stressed, their microbiomes can protect them from bleaching. In addition, we can now pinpoint specific genes in coral animals and their photosymbionts that may be involved in this thermal stress response.”

While previous studies on the mechanisms underlying corals’ heat-stress tolerance tended to focus only on the animals or their photosymbionts, this new study analyzed how the entire holobiont (the coral animal, its photosymbionts, and microbiome) is involved in the stress response. 

By performing a heat-stress experiment on three species of corals known to differ in their sensitivities to heat stress and the composition of their holobionts, the researchers investigated the varying contributions of each holobiont member to the corals’ stress tolerance. 

“Our goal with this research was to determine if there have been lineage-specific innovations to heat stress in corals and their algal photosymbionts, as well as whether all members, including bacterial communities, differentially contribute to holobiont robustness,” said co-author Viridiana Avila-Magaña, a former doctoral student at Penn State. 

The gene-expression data revealed that the three coral holobionts differed in their responses to heat-related stress, and that members of each holobiont had different contributions to the corals’ ability to cope with thermal stress. The scientists concluded that the greater thermal tolerance observed in some coral holobionts, such as the starlet coral, are partly due to the higher number and density of their thermally resistant microbes in their microbiomes.

“We found that some corals harbor a stable and diverse microbiome translating to a vast array of metabolic capabilities that we have shown remain active during the thermal challenge. By contrast, we found that less thermally tolerant species had reduced bacterial activity and diversity,” reported Dr. Avila-Magaña.

“Corals have been highly impacted by climate change, and the methods we developed in our study represent an excellent tool for scientists trying to understand the adaptive potential of populations and species,” the researchers concluded. 

The study is published in the journal Nature Communications.

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By Andrei Ionescu, Earth.com Staff Writer