No one knows for sure how many kinds of staghorn corals there are, but scientists estimate there may be nearly 400 species. And only scientists can tell them apart; these corals grow in a confusing variety of shapes and colors. A single small reef may have hundreds of Acropora colonies growing on it.
But in all their variety—from flat platelike colonies to pillowlike clumps to the branching, antlerlike form from which they get their common name—these fast-growing corals are consummate reef builders and important members of coral reef communities around the world.
Coral reefs around the world are in danger. Silt (fine soil) smothers coral when it washes off the land from farm fields, roads and building sites. More towns and resorts near shore mean more sewage, oil and chemicals in the water. Global warming and changes in weather patterns create conditions that corals can't survive. Even recreational diving on reefs takes a toll: boat anchors break off coral heads, and corals die where divers kick or grab them.
Acropora corals grow fast in order to shade out other corals and gain more space on the reef. But fast is relative in the coral world; a colony of staghorn coral may only grow four inches (10 cm) per year.