Coral reefs are built by and made up of thousands of tiny animals—coral “polyps”—that are relatedto anemones and jellyfish.
Different types of coral reefs:
- Fringing reefs are reefs that grow directly from a shore. They are located very close to land,and often form a shallow lagoon between the beach and the main body of the reef.
- Barrier reefs are extensive reefs that parallel a shore, and are separated from it by lagoon.
- An atoll is a roughly circular oceanic reef system surrounding a large central lagoon.
Favorable conditions for growth:
- Sunlight: Corals need to grow in shallow water where sunlight can reach them. Coralsdepend on the zooxanthellae (algae) that grow inside of them for oxygen and other things,and since these algae needs sunlight to survive, corals also need sunlight to survive. Coralsrarely develop in water deeper than 165 feet (50 meters).
- Clear water: Corals need clear water that lets sunlight through; they don’t thrive well whenthe water is opaque. Sediment and plankton can cloud water, which decreases the amount of
sunlight that reaches the zooxanthellae.
- Warm water temperature: Reef-building corals require warm water conditions to survive.Different corals living in different regions can withstand various temperature fluctuations.However, corals generally live in water temperatures of 68–90° F or 20–32° C.
- Clean water: Corals are sensitive to pollution and sediments. Sediment can create cloudywater and be deposited on corals, blocking out the sun and harming the polyps. Wastewaterdischarged into the ocean near the reef can contain too many nutrients that cause seaweedsto overgrow the reef.
- Saltwater: Corals need saltwater to survive and require a certain balance in the ratio of salt towater. This is why corals don’t live in areas where rivers drain fresh water into the ocean
(“estuaries”).