In fact, many Pacific islands are made solely of coral that is usually resting on top of a sea mount of volcanic rock. The Great Barrier Reef, in Australia, is the longest continuous series of reefs in the world and is made up of over 1500 individual reefs that rest on a continental shelf that is generally less than 50m deep. There is a rich diversity of fishes and invertebrates on coral reefs. In fact, the diversity of organisms is often argued to be greater than any environment on the planet. Species diversity of a wide range of tropical taxa is greatest in waters around Indonesia.
Rocky reefs are more typical of subtropical, temperate and sub-polar latitudes.
The reefs are generally covered with rich algal habitats. Laminaria is the Northern Hemisphere equivalent. Rock reefs are often subjected to heavy seas that test necessarily robust assemblages of plants and animals. There is great beauty on rocky as well as coral reefs. On rocky reefs the algae move gracefully with the waves, caves and tunnels are often the most colourful areas with a rich diversity of sponges, sea squirts and anemones.