Coral reefs are the most diverse marine ecosystems on Earth. Rising ocean temperatures threaten reefs by causing scleractinian corals to lose their dinoflagellate photosymbionts (Family: Symbiodiniaceae) in a process called coral bleaching, which often kills the coral host. While stressors that induce bleaching are relatively well documented, the physiological mechanism(s) underlying the bleaching process remains disputed. Viruses in the family Alvernaviridae, which have been identified in the photosymbionts of multiple coral species, potentially cause bleaching signs by lysing coral photosymbionts. This study tracks the abundance of Alvernaviridae strains in five colonies of the stony coral Pocillopora verrucosa exposed to heat stress for five days. We paired major capsid protein gene amplicon sequencing data with transmission electron microscopy images of photosymbiont cells to correlate viral abundance with photosymbiont health over time.
Results/Conclusions
Virus-like particles appeared in photosymbionts after 24 hours of heat stress, concurrent with photosymbiont degradation signs. Additionally, the relative abundance of certain Alvernaviridae strains changed over time. Our findings help clarify the role of Alvernaviridae in coral bleaching and provide a solid basis for further studies of this relationship in stony corals worldwide.