Reef-building corals farm and feed on their photosynthetic symbionts

Summary

This study elucidates how reef-building corals overcome nutrient limitation in oligotrophic waters by farming their algal symbionts. Through long-term experiments, the authors show that dissolved inorganic nitrogen and phosphorus uptake by zooxanthellae is sufficient to support rapid coral growth, with corals acquiring these nutrients via selective digestion of excess symbiont cells. A large-scale natural experiment (seabird-fertilised versus unfertilised reefs) validates that efficient nutrient utilisation by symbiotic corals enhances growth at the ecosystem level.

Regional applicability

This is a fundamental marine biology study conducted on tropical coral reef ecosystems (not United Kingdom-based). The findings have no direct applicability to UK terrestrial or temperate marine farming systems, though the mechanisms of host–microbe nutrient exchange may inform understanding of symbiotic relationships in other agricultural contexts.

Key measures

Nitrogen and phosphorus budgets in host and symbiont compartments; rates of symbiont digestion; coral growth rates under varying nutrient regimes; ecosystem-level coral growth in reefs with and without seabird fertilisation

Outcomes reported

The study demonstrated that symbiont uptake of dissolved inorganic nitrogen and phosphorus is sufficient to sustain rapid coral growth, and identified that corals acquire these nutrients through farming and selective digestion of excess symbiont cells. A natural ecosystem experiment showed that enhanced nutrient availability from seabird fertilisation increases coral growth in symbiotic corals.

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