Ocean warming intensifies viral outbreaks within corals

The breathtaking colors of reef-building corals in part come from photosynthetic algae that live inside the corals. A three-year Rice University study has found that viruses may increase their attacks on these symbiotic algae during marine heat waves.

Few studies have examined how heat and other forms of stress affect coral virus outbreaks, and fewer still have looked at the reef-scale dynamics of those outbreaks. The U.S. National Science Foundation-supported study published in ISME Communications does both.

It is also the first research to analyze the reef-wide prevalence, persistence, triggers and health impacts of dinoflagellate-infecting RNA viruses, or dinoRNAVs, single-stranded RNA viruses that infect the symbiotic algae that live inside the corals.

Lead author Lauren Howe-Kerr said coral and marine disease researchers are paying closer attention to coral viruses in the wake of studies that found evidence suggesting viral infections of symbiotic dinoflagellates might be responsible for stony coral tissue loss disease. One of the deadliest coral diseases ever recorded, SCTLD has been decimating reefs in Florida and the Caribbean since it was first identified in 2014.

The study was carried out at the NSF-funded Moorea Coral Reef Long-term Ecological Research site on the South Pacific island of Moorea in French Polynesia. Moorea, which is about 20 miles from Tahiti, is ringed by coral reefs.

Samples from 54 coral colonies around the island were collected twice a year between August 2018 and October 2020. The warmest water temperatures during that span were in March 2019. Reefs across the island suffered heat-related stress during this period, including widespread bleaching.

The study sites were in a variety of reef zones that were subject to different kinds of environmental stress. For example, ocean-facing forereefs are deeper, with cooler and more consistent water temperatures, while near-shore fringing reefs in lagoons are subjected to the highest temperatures and greatest temperature variability.

"Viral productivity will likely increase as ocean temperatures continue to rise," said co-author Adrienne Correa. "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."