Peptide biomarkers predict coral survival from heat stress

Researchers have discovered molecular characteristics that distinguish which corals can withstand a bleaching event, and which are susceptible.

When seawater temperatures become too hot, corals expel their colorful algal symbionts.. The algae that live within corals support them by supplying nutrients and energy from photosynthesis. Corals are animals and cannot make their own food. The loss of their algae turns the corals white. The corals then become weak, struggle to reproduce and are at risk for widespread demise.

A recent project showed that the type, amount, and interactions of proteins and peptides –- the proteomics of the coral – is a key indicator of whether it could overcome a thermal-induced bleaching event. 

“Some corals are very resilient and very robust. To improve reef restoration efforts, we performed studies to determine how to identify and select resilient coral for propagation purposes and to assure they would have offspring,” said Brook L. Nunn, research associate professor in the Department of Genome Sciences at the University of Washington School of Medicine in Seattle. 

She heads the UW Environmental Proteomics Lab, which uses bioinformatics and tandem mass spectrometry to catalog and quantify proteins and peptides in samples from the environment. The lab focuses on marine environments and, as part of the School of Medicine, incorporates marine diagnostics as one aspect of its diverse research activities. Nunn is particularly interested in understanding life forms in extreme conditions and the limits of life and is a co-lead of NASA’s Network for Life Detection (NFOLD). She is also on the UW Astrobiology Program faculty.

Organisms produce an array of proteins to carry out a myriad of functions. Amassing information about proteins produced by life under particular conditions can offer clues to how life is sustained and what nutrients limit or enhance their success. 

Based on their studies in coral, the researchers determined that the protein signature associated with recovery from a thermal bleaching event could act as a signature for hardiness. 

“This approach boils down complexity to a few biomarkers that are trackable,” Nunn said. “These diagnostic biomarkers in coral could apply in managing and restoring coral reefs.”

Currently, marine biologists randomly select small fragments of coral to try to regrow coastline and offshore coral beds. The UW team set off to determine if they could provide a more science-based approach to the selection process. 

“We have now identified peptide-based biomarkers that can be rapidly measured from rice-sized snippets of coral samples by using targeted proteomics, allowing us to select the best candidate corals for propagation and enhance reef resilience in the face of climate change,” she added. 

A scientific paper describing this work was featured in Communications Earth & Environment, a Springer Nature scientific journal. The project brought together collaborators that included four members of Nunn’s team in genome sciences; UW fisheries and aquatic scientists; UW biology department faculty; and environmental researchers and biologists from UCLA and Villanova University.

"The work provides a blueprint for identifying corals most likely to survive future bleaching events, offering critical insights to predict and enhance reef resilience in a rapidly warming world,” said senior researcher Jaqueline Padilla-Gamiño, associate professor of aquatic and fisheries sciences at the UW.

Excess heat can also harm the coral microbiome -- the collection of tiny organisms like bacteria and archaea that live in the coral’s mucus, gastric cavity, or stony skeleton. Disrupting this microbiome could damage some of the coral’s protective defenses against disease. 

Coral death, if widespread, can cause the downfall of total biological communities that make the reef their home. 

The coral species studied in a recent project was considered to be one of the most resistant to thermal bleaching events. However, mortality due to bleaching events sometimes occurs among this coral. 

Nunn recalled. “Jackie’s team collected many samples through time to understand nutritional status on egg development.  As we discussed all the projects we could do, I proposed that we conduct a secondary blind study on the corals we already sampled to examine their molecular physiology before bleaching. I figured that quantitative proteomic analyses could unravel active and failing metabolic pathways.”

She pointed out that the genome of corals is not fully annotated, as it is in some other animals. This makes it difficult to study the effects of protein-coding and non-coding genes on coral survival. 

The researchers experimentally bleached a type of Hawaiian coral called Montipora capitata to explore the differences between the corals that recovered and those that died. The scientists chose this species because it tends to have a greater heat tolerance than other species in Hawaii. 

Corals from this species were monitored by Padilla-Gamiño and her team for eight months after bleaching to pick out those with long-term resilience.

The researchers emphasized that the coral’s metabolic capacity before, during, and after bleaching is critical to survival. Without adequate carbon and nitrogen, coral cannot replace its cells, repair its tissues, or defend against infections.

“This suggests that the thermal threshold and physiological condition of the coral host may be the most important factors in determining resilience to bleaching stress and mortality,” the study scientists noted. 

Additional research showed that, before thermal stress, coral better suited to withstand the effects of heat had a more diverse microbiome and produced abundant proteins for acquiring carbon, keeping beneficial algae around, and resisting pathogens. The coral that couldn’t tolerate heat stress had a protein signature congruent with early rejection of the helpful algae. Those susceptible corals also utilized urea, a chemical important in cellular metabolism, to obtain carbon and nitrogen. 

Corals that can outlast heat stress and bleaching can regain their algal symbionts, fully get back to their previous physiological performance and produce healthy reproductive cells for spawning new generations. The time for recovery does vary, from a few weeks to up to years. 

The next phase of this research will be to test the peptide biomarkers they discovered on a variety of other corals to determine how translatable the science is to coral on other coastlines. 

Applying new knowledge about what enables some corals to survive is important because large-scale, thermal-induced coral bleaching events are becoming more common worldwide. This increase is driven by rising temperatures on the surface of seawater around the globe, as well as from marine heatwaves along coastal regions. 

“Our research highlights the critical molecular and microbiome factors that support coral resilience,” Padilla-Gamiño noted. “By identifying key biomarkers of survival, we can develop targeted strategies for reef conservation and restoration, ensuring these ecosystems endure for future generations."

The work on this project was supported in part by the University of Washington’s Proteomics Resource (UWPR95794), by National Foundation grants IOS-IEP 1655682 , IOS-IEP 1655888-IOS 2041497, an NSF GFRP award and an NSF CAREER 2044840 award, an  NIH-F31 award, an Alfred P. Sloan Research Fellowship and  by CCN (private funds to support environmentally relevant research aimed at making a difference). 

Read the research paper: Protein signatures predict coral resilience and survival to thermal bleaching events | Communications Earth & Environment

For details about UW Medicine, please visit http://uwmedicine.org/about.