Safe inside the corals, the plantlike algae flourish in the tropical sun. In turn, the algae produce sugars and proteins that help nourish the corals. What corals build, other forces tear down Reefs change from moment to moment in an ever-shifting balance of growth and destruction. Sponges and clams tunnel into the coral rock, weakening the reef. Parrotfishes and puffer fishes nibble and crunch, changing coral rock to coral sand.
Butterflyfish pick at individual coral polyps .
Hurricanes roar over tropical seas, bringing crashing waves and surges that can pound entire reefs into rubble or smother them beneath churning silt and sand. But change and destruction open opportunities as well. New corals take hold where older ones have broken away. Sponges, other animals and algae move in to colonize places left bare by storms or grazers. Staghorn corals grow rapidly, but are easily damaged in storms.