Because algae and reef-building corals need sunlight for photosynthesis, the reef must grow relatively near the ocean's surface to survive.
(algae and reef-building corals; need; sunlight for photosynthesis) (the reef; must grow; L:relatively near the ocean's surface) (the reef; to survive; )
algae and reef-building corals the reef the reef
need must grow to survive
sunlight for photosynthesis
L:relatively near the ocean's surface