Coral reefs are underwater ecosystems composed of calcium carbonate structures secreted by corals. They are built by colonies of tiny marine animals called polyps that cluster together in waters with few nutrients. Animals have adapted to use coral reefs as a safe habitat and find food sources within the reefs.

1. The Coral Reefs are diverse underwater
ecosystems held together by calcium
carbonate structures secreted by corals.
Coral reefs are built by colonies of tiny animals
found in marine waters that contain few
nutrients. Most coral reefs are built from stony
corals, which in turn consist of polyps that
cluster in groups.
Information found here:
http://en.wikipedia.org/wiki/Coral_reef

2. HOW ARE ANIMALS ADAPTED TO CORALS REEF?
Animals have adapted to the Corals Reef by
using it at a safe place to stay away from
predators.
Animals have also adapted to get their food
source from in the corals reef.