1. Coral Reefs

2. Coral reefs are usually found in warm, clear, shallow ocean habitats that are rich in life
The reef's massive structure is formed from coral polyps, tiny animals that live in colonies; when coral polyps die, they leave behind a hard, stony, branching structure made of limestone.
Coral reefs develop in shallow, warm water, usually near land, and mostly in the tropics; coral prefer temperatures between 70 and 85 ° F ( °C).

4. Types of Reefs:
Fringing reefs are reefs that form along a coastline. They grow on the continental shelf in shallow water.
2. Barrier reefs grow parallel to shorelines, but farther out, usually separated from the land by a deep lagoon. They are called barrier reefs because they form a barrier between the lagoon and the seas, impeding navigation.
3. Coral Atolls are rings of coral that grow on top of old, sunken volcanoes in the ocean. They begin as fringe reefs surrounding a volcanic island; then, as the volcano sinks, the reef continues to grow, and eventually only the reef remains.

5. 1. Fringing Reef: Polynesian island

6. 2. Barrier Reef

7. The Great Barrier Reef (off the coast of NE Australia) is the largest coral reef in the world. It is over 1,257 miles (2000 km) long.

8. 3. Tuanake Atoll in French Polynesia

9. What are coral polyps? There are two types of corals:
Coral polyps are small marine invertebrate animals. Most polyps live in large colonies.
There are two types of corals:
Hard corals: secrete calcium carbonate skeleton (forms the reef when the coral polyp dies)
Soft corals: have soft internal skeletons

10. Great Star Coral: each polyp is about 1cm in diameter

11. 1). The mouth is surrounded by tentacles armed with stinging cells for capturing plankton. During the day these tentacles are folded in the digestive sac.
2). Microscopic single-celled algae that give the coral its green, blue or brown colour are located in the tissue of the living coral.
(3). These symbiotic algae (Zooxanthellea) process the wastes produced by the polyps. Through photosynthesis they generate oxygen and organic compounds which the polyps themselves can use. They may also help the polyp lay down calcium carbonate.

12. Corals are carnivorous!!
Corals are carnivores that eat zooplankton (like copepods and tiny marine larvae). They catch food using tentacles that surround the mouth; the tentacles have poisonous stingers (called nematocysts)
Zooplankton: Small animals that generally have limited or no swimming ability and are transported through the water by currents and tides
examples: amphipods, shrimp, fish larvae, copepods, invertebrate larvae, protozoans and rotifers

14. Coral reproduction:
Corals reproduce either asexually (the polyp grows another polyp out of its side) or sexually (polyps can be male, female, or male and female)

15. Predators
Corals are eaten by the crown-of-thorns (a large starfish that eats coral polyps), parrotfish, and other animals.

16. Threats to Coral Reefs:
Human Contact: Touching Reefs, even slightly, can harm them. Boats and dropped anchors can cause severe damage to these fragile ecosystems. Frequent human contact kills the reefs over time. 
Runoff Water: Silt from eroded soil in runoff water can block sunlight. Without sunlight, photosynthesis does not occur and reefs gradually die. 
Sewage: Untreated or improperly treated sewage promotes the growth of algae, which harms coral reefs. 
Cyanide Fishing: Some fishermen stun fish by squirting cyanide, a very toxic poison, into reef areas where fish seek refuge. The poison does not kill, but disorients the fish in the coral where they hide.  The fisherman then rip apart the reefs with crowbars to capture the fish. In addition, cyanide kills coral polyps and the symbiotic algae and other small organisms necessary for healthy reefs. Cyanide fishing is common in the South Pacific and Southeast Asia. 
Fertilizers & Pollution: Fertilizer runoff, pesticides and other chemicals can poison reefs. 
Blast Fishing: Shock waves from blast fishing can destroy coral reefs.
Increased UV rays: causes coral bleaching (when the zooxanthellae die and leave the coral white. 

17. Reef Diversity

18. Blue-green coral (left) and orange popcorn coral (right) are just a few examples of the variety of colors found in tropical corals. This color may be primarily from their symbiotic zooxanthellae (as in the blue-green coral) -or- produced by the coral animal itself (as in the orange popcorn coral).

19. Cavernous star coral heads may be over five feet wide.

20. Fire coral looks like a miniature castle.

21. Tube coral, is one of the more delicate species
Tube coral, is one of the more delicate species. Each polyp makes a long tube attaching to its neighbour at the bottom only - making it easily broken in storms, as in this picture.

22. Table coral is closely related to staghorn coral but grows like a table from a stump. These table corals are often the home for small fish hiding in cracks and crevices. Here (right) a diver just swam over this table coral and the fish "dove for cover" in the cracks. New research done at Heron Island shows that most of these little fish never leave their table coral - they come in as babies and spend their entire life on one table coral.

23. Fish may depend on the coral for protection
Fish may depend on the coral for protection. This mound of staghorn coral has a small group of fish that use it for cover.