Coral Reefs and Oil Spills: A Guided Tour

November 2, 2006

Note: The following guided tour refers only to coral reefs found in shallow tropical waters.

Part 1

One of nature’s most spectacular creations, coral reefs are also among the most complex, diverse, and economically valuable ecosystems in the world. Sadly, coral reefs are being rapidly damaged from both natural and human causes. This tour will give you a basic overview of coral reefs, some of the threats they face, and some of the ways we can restore reefs that have been damaged.

Individual corals, or polyps, are sac-shaped organisms, each with a central mouth surrounded by a ring of tentacles.

What are coral reefs?


Tiny individual coral polyps, related to sea anemones, create reefs by secreting limestone skeletons. Coral polyps divide as they grow and form coral colonies, creating a coral reef.

Each individual polyp harbors symbiotic algae, called zooxanthellae. Zooxanthellae use sunlight to make oxygen and food that the polyps use, and the polyps, in turn, produce wastes that the zooxanthellae need. Thus, coral reefs can only grow where water is clear enough to allow adequate light penetration for photosynthesis.

Not all corals build reefs, however. Soft corals, which include sea fans, sea plumes, and sea whips, are important components of coral communities.

Coral reefs provide food and shelter for many fish and invertebrates. For example, sea turtles shelter in reef overhangs and forage for sponges and other food items; manatees feed in reef-associated seagrass beds.

How are coral reefs structured?

Coral reefs form in regions of the world where there are warm currents, mainly between the Tropics of Cancer and Capricorn. There are four main reef types: fringing, barrier, atolls, and patch reefs.

Fringing (or apron) reefs directly border shorelines:


Barrier reefs are similar to fringing reefs except that they are separated from the shoreline by lagoons that are often deep and wide:


Atolls are circular-shaped reefs that form on the rim of submerged volcanic islands; patch reefs are small, isolated formations that are not attached to a major reef structure:


Figures source: Mann, K. H., 1982, Ecology of Coastal Waters – A Systems Approach, Chapter 6: Coral Reefs, 160-182, Berkeley and Los Angeles: University of California Press (as modified).

Continue the tour at NOAA



  1. another interesting site is
    CREST: Coral Reef Education for Students and Teachers

  2. Thank you for giving us this link. I’m sure the many students (as well as our other readers of course!) who continue to use this site for their research and assignments will find it very useful.

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