Coral reefs

Basic structure The ability of coral to build a massive wave-resistant structure is crucial to the survival of many of the animal and plant communities. Major structural and architectural feature of a living reef is a coral embankment reaching to just below the surface of the water.

Basic structure Hundreds of species of encrusting organisms cover the surface of a reef and bind the coral branches together. Space to grow is one of the major limiting factors on the reef, so any scar put in the coral by a careless fin or break of the coral will be quickly taken over by a boring sponge or bivalve mollusc and may signal the death of the entire coral colony. Be careful!

Basic structure Built of skeletons of tiny marine invertebrate organisms.  Animals themselves tiny, but calcium carbonate skeletons build up and can be extremely strong.  Corals die, but reef remains. Many organisms add to reef structure including algae, molluscs, sponges and worms.  Algae extremely important. While reefs can last for millions of years, the living surface is extremely fragile and easily damaged. 

Value Tourism.  Reefs are beautiful and interesting.  Bring billions each year.  U.S. gets nearly 2 billion a year from reef-visiting tourists in Hawaii and Florida keys.  Imagine how important to developing nations. Food source.  Can provide 10% of world's supply of fish, molluscs and crustaceans.  This is sustainable.  (approx 70 million to U.S.).

Value Complex ecosystem which supports species diversity. Habitats for many organisms.  Diverse environment in relatively small area.  Can have organisms adapted to wave action, those that survive in sandy areas, homes for organisms that do not move (sessile), mangrove organisms, and clingers to rocks on rocky shores. Coral reefs contain 22 of the 23 animal phyla found on the planet. Symbiotic relationships are common. Act as wave barriers and protect shorelines. Pictures from: http://state-of-coast.noaa.gov/bulletins/html/crf_08/national.html 

Types of reefs Fringing reefs and bank barrier reefs In a fringing reef the coral projects from the rocky shore and the reef remains attached to the land. There is no lagoon between the reef and the land mass. The corals are highly varied and often there is no dominant type. Surrounding it are patch reefs composed of a few scattered corals

Fringing reef “An aerial view of a shallow- water, Caribbean fringing reef. Notice the "spur and groove" configurations caused by alternating coral buttresses and channels. The lighter band close to shore denotes a rubble/sand zone."

Bank barrier reef Fringing reefs can gradually shade into bank barrier reefs typical of the Caribbean. They have platforms that are much less extensive and are much closer to the shore than the ancient barrier reefs of the Pacific and lagoons that are much shallower. Fall between fringing and true barrier reefs. Atlantic reefs are less than 20,000 years old.

Bank barrier reef Fringing reefs can gradually shade into bank barrier reefs typical of the Caribbean. They have platforms that are much less extensive and are much closer to the shore than the ancient barrier reefs of the Pacific and lagoons that are much shallower. The bank barrier reefs in the Atlantic are less than 20,000 years old, while the Pacific reefs are hundreds of thousands of years old. How can you explain this discrepancy?

Barrier reefs A barrier reef is a coral reef separated from the land mass by a large lagoon with comparatively deep water. Barrier reefs occur in association with continental land masses. Reefs keep growing out to sea. why? Great rear reef of Australia extends for 1200 mile. Second-largest is off Yucatan coast of Mexico and Belize.

Barrier reefs Barrier reefs grow because of gradual sinking of the land on which they sit or because of rising ocean levels. Caribbean barrier reef probably grew due to rising ocean levels.

Barrier reef

Atoll   An atoll is an isolated ring of coral islands and reefs that nearly, or entirely, enclose a lagoon. Parts of the reef may stick out of the water as coral islands.  There are over 300 atolls in the Indo-Pacific.  

Atolls Develop as a volcanic island slowly sinks due to its weight and the fringing reefs on its shore gradually become barrier reefs as water gets between the reef and the sinking island shore.  Finally have the ring. Darwin developed this theory.  Relates all 3 types of reef.  How would you show that Darwin was correct?

Jamaican reef Back reef;this the reef  shore zone. Area is protected from the surf and is dotted with isolated coral heads. Turtle grass (Thalassia testudinum ) harbors its own community of sea urchin conchs etc. This is the first place to snorkel. See Kaplan for thorough descriptions of the organisms to be found in each area of the reef.

The reef crest In the protected rear zone of the back reef you’ll find boulder corals and those that tend to form large and massive hands such as the brain corals. In wavy areas you will see gorgonian corals.

Reef flat This zone is filled with rubble from broken corals. The water can be quite shallow here so be careful when snorkeling. It is easy to get cut or stung.

Buttress zone A favorite snorkel for our students. Swim into an over the sandy channels between the massive buttresses of boulder coral. Be sure to read Kaplan’s wonderful description of this area before we go so you will know what to look for.