Coral reefs are highly diverse ecosystems that thrive in nutrient-poor waters, a phenomenon frequently referred to as the Darwin paradox¹. The energy demand of coral animal hosts can often be fully met by the excess production of carbon-rich photosynthates by their algal symbionts^2,3. However, the understanding of mechanisms that enable corals to acquire the vital nutrients nitrogen and phosphorus from their symbionts is incomplete^4,5,6,7,8,9. Here we show, through a series of long-term experiments, that the uptake of dissolved inorganic nitrogen and phosphorus by the symbionts alone is sufficient to sustain rapid coral growth. Next, considering the nitrogen and phosphorus budgets of host and symbionts, we identify that these nutrients are gathered through symbiont ‘farming’ and are translocated to the host by digestion of excess symbiont cells. Finally, we use a large-scale natural experiment in which seabirds fertilize some reefs but not others, to show that the efficient utilization of dissolved inorganic nutrients by symbiotic corals established in our laboratory experiments has the potential to enhance coral growth in the wild at the ecosystem level. Feeding on symbionts enables coral animals to tap into an important nutrient pool and helps to explain the evolutionary and ecological success of symbiotic corals in nutrient-limited waters.

珊瑚礁是高度多样化的生态系统，在营养贫乏的水域中繁衍生息，这种现象通常被称为达尔文悖论¹ 。珊瑚动物宿主的能量需求通常可以通过其藻类共生体过量产生富碳光合产物来完全满足^2,3 。然而，对珊瑚从共生体中获取重要营养物质氮和磷的机制的理解并不完整^4,5,6,7,8,9 。在这里，我们通过一系列长期实验表明，仅共生体对溶解的无机氮和磷的吸收就足以维持珊瑚的快速生长。接下来，考虑宿主和共生体的氮和磷预算，我们确定这些营养物质是通过共生体“耕作”收集的，并通过消化多余的共生体细胞转移到宿主。最后，我们利用大规模的自然实验，其中海鸟使一些珊瑚礁而不是其他珊瑚礁受精，以表明我们实验室实验中建立的共生珊瑚对溶解的无机养分的有效利用有可能促进野生珊瑚的生长。生态系统层面。以共生体为食使珊瑚动物能够利用重要的营养库，并有助于解释共生珊瑚在营养有限的水域中的进化和生态成功。