Coral Viruses Worsening Because of Increasing Ocean Temperatures, Three-Year Study Finds

The climate crisis has contributed to a major loss of coral reefs, and now, a three-year-long study has identified further threats to reef systems as ocean temperatures increase. Ocean warming can trigger viral outbreaks that impact coral reefs, according to the newly published research.

The researchers looked at corals in the South Pacific in one of very few studies to explore how heat can impact viral outbreaks in corals, particularly across entire reefscapes. The study is the first to look into “dinoflagellate-infecting RNA viruses” (dinoRNAVs), from what triggers them to how they impact the coral. These dinoRNAVs are viruses that infect the algae living within corals.

The study, published in the journal ISME Communications, investigated how viruses could attack the photosynthetic algae that live inside corals and give them their vibrant colors. The algae, which have a symbiotic relationship with coral, can experience more attacks from viruses as ocean temperatures increase.

Researchers collected samples from 54 coral colonies, with different reef zones, around Mo’orea island in French Polynesia. They retrieved samples twice per year from August 2018 to October 2020, noting the most ocean warming during March 2019. During this time of heightened ocean warming, reefs experienced heat-related stress, including coral bleaching.

“Our work provides the first empirical evidence that exposure to high temperatures on the reef triggers dinoRNAV infections within coral colonies, and we showed those infections are intensified in unhealthy coral colonies,” Lauren Howe-Kerr, lead author of the study and postdoctoral researcher at Rice University, said in a statement.

The team found dinoRAV infections in more than 90% of the colonies at any point of the study period. Howe-Kerr explained that the viruses differed in composition and variety for different reef zones, showing that the corals’ environment can also affect outbreaks.

About half of the sampled colonies experienced partial mortality, and ocean-facing forereefs experienced the worst of these impacts. In 2019, when ocean temperatures were at their highest during the study period, the team found more variety of RNA viruses, which could mean an increase in viral production. This was especially true in the areas that were impacted by partial mortality.

“Viral productivity will likely increase as ocean temperatures continue to rise,” said Adrienne Correa, marine biologist and co-author of the study. “It’s important to learn as much as we can about host-virus interactions, because they have the potential to alter the foundational symbiosis that underpins coral reef ecosystems.”

The authors concluded that dinoRNAVs may increase their productivity under warming temperatures, and individual and reef system health may both further influence viral productivity. Further, the researchers warned that viral outbreaks can be expected to worsen with ongoing climate change and ocean warming.