Coral and Coral Reef

As an underwater environment, coral reefs offer a wide variety of habitats for plants and animals. Phytoplankton, benthic algae, and bacteria are at the base of the food web. They serve as food for the large variety of animals in the coral-reef ecosystem. If you ever visit a coral reef, you may find that greenery seems relatively scarce; however, six inconspicuous types of plants make coral reefs the marine community with the highest primary productivity. These are the calcareous and noncalcareous green algae, red algae, and brown algae; the hidden ("cryptic") zooxanthallae living in coral tissue and green filamentous algae living in the porous limestone substrate; and the microscopic phytoplankton.

In addition to the species of small zooplankton drifting over coral reefs, the reef water column supports jellyfish and other large invertebrates such as cuttlefish, squid, and octopus; many species of fish and marine reptiles (snakes and turtles); and the occasional mammal species (seals, porpoises, and manatees). As many as 500 species of fish may inhabit a given coral reef. Many of these fish species defend a territory, while others occur in large schools. Many benthic species occur in and on the reef as well. These include the corals themselves, barnacles, oysters, clams, lamp shells, and polychaete worms. All told, as many as 150,000 species may live in some coral reefs.

Coral reefs are subject to small-scale erosion caused by certain organisms that bore into the reef substrate, including bacteria, fungi, algae, sponges, worms, sea urchins, and predatory clams. Their activities create open spaces in the reef, increasing the diversity of habitats and allowing more species to inhabit the ecosystem.