藻类作为珊瑚的共生体，为珊瑚提供食物和氧气。

The algae act as ___symbionts for the coral, providing it with food and oxygen.

这些藻类作为珊瑚的共生体，帮助它们进行光合作用。

These algae serve as ___symbionts for corals, helping them perform photosynthesis.