corals

• Coral first appeared in the Cambrian period. 
• Corals can be solitary where one polyp secrets a single skeleton and lives alone. They can also be colonial where may polyps live together. 
• Most corals have septa which are plates that increase the strength of the calcium carbonate skeleton. 
• Coral contains an algae called zooxanthellae. Where the coral and the algae have a symbiotic relationship. The algae can photosynthesis due to the chloroplasts in their cells, they use the waste of the corals and the corals use the algae waste. 
• 90% of the organic material photosynthetically produced by the zooxanthellae is transferred to the host coral. 
• Soft bodied polyps sit on top of the coral and extent their tentacles to extract food by paralysing them or trapping them in mucus. 
• Solitary corals live in temperate or tropical water. Reef building corals can only grow in tropical waters between 30 degrees n+s of the equator. They need to grow at or just below sea level where light levels are high, they also need clear water to allow the light through. They also need clean waters so no mud or sediment can clog their pores, they live in high energy environments to circulate oxygen and nutrients. They need warm waters of between 23 and 29 dc. 
• Coral skeletons are made of calcium carbonate so modern reefs are made of limestone. Using uniformitarianism we can determine the environment the rocks were deposited in.