![]() The heterogeneous reef structure also fosters niche specialization and biological diversification. ![]() The accretion of corals’ calcium carbonate skeletons generates intricate tridimensional structures that provide habitat, nursery, and breeding grounds for reef and offshore species. The complex symbioses and interactions between corals, microbes, and viruses that make up a coral holobiont provide organic matter and nutrient turnover that sustains large trophic webs that extend well beyond the reef. We propose that combined predation pressures from fishes and viruses control energy fluxes, inhibiting the detrimental accumulation of ecosystem energy in the microbial food web.Ĭoral reefs harbor over 30% of the ocean’s biodiversity but are some of the most impacted ecosystems by anthropogenic threats. The results presented here support the hypothesis that viral predation of bacteria is associated with high coral cover and, thus, coral health and stability. However, these relationships were non-linear, with reefs at the higher and lower ends of the coral cover continuum displaying a narrow combination of abiotic and biotic variables, while reefs at intermediate coral cover showed a wider range of parameter combinations. While fish biomass was not a strong predictor of coral cover, the relationship between fish and corals became apparent when analyzed in the context of viral predation: high coral cover (> 50%) occurred on reefs with a combination of high predator fish biomass (sum of sharks and piscivores > 200 g m −2) and high virus-to-bacteria ratios (> 10), an indicator of viral predation pressure. Statistical learning showed that the abundance of turf algae, viruses, and bacteria, in that order, were the variables best predicting the variance in coral cover. Here, we investigated the relationships between live coral cover and viruses, bacteria, benthic algae, fish biomass, and water chemistry in 110 reefs spanning inhabited and uninhabited islands and atolls across the Pacific Ocean. We hypothesize that viral predation of bacteria has analogous effects to the top-down pressure of macroorganisms on the trophic structure and reef health. Viruses that infect bacteria can control microbial densities and may positively affect coral health by controlling microbialization. A major biological component that has been poorly integrated into the reefs' trophic studies is the microbial community, despite its role in coral death and bleaching susceptibility. This variability is likely a result of the complex interactions between coral reefs’ biotic and abiotic dimensions. However, the extent of these cascading effects can vary considerably across space and time. Predation pressure and herbivory exert cascading effects on coral reef health and stability.
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