Reef-Building Corals Feed on Photosynthetic Symbionts

Coral reefs, often existing in nutrient-poor waters known as the Darwin paradox, are highly diverse ecosystems.

Coral animals primarily rely on their algal symbionts to satisfy their energy demands, mainly through the production of carbon-rich photosynthates. However, our understanding of how corals obtain essential nutrients such as nitrogen and phosphorus from these symbionts remains incomplete.

Through extensive long-term experiments, we've shown that the symbionts' uptake of dissolved inorganic nitrogen and phosphorus alone can sustain rapid coral growth.The team also discovered a process termed as "symbiont farming," where corals obtain these nutrients from their symbionts and transfer them to the host through the digestion of surplus symbiont cells.

Additionally, a natural experiment involving seabird-induced reef fertilization highlights how the efficient use of dissolved inorganic nutrients by symbiotic corals in our laboratory experiments could potentially boost coral growth in the wild on a larger scale.

In essence, coral animals accessing this nutrient source by consuming their symbionts is a crucial factor explaining the evolutionary and ecological success of symbiotic corals in nutrient-scarce marine environments.