Corals

Corals live in nutrient poor waters and have certain zones of tolerance to water temperature, salinity, UV radiation, opacity, and nutrient quantities. Scleractinian corals build skeletons of calcium carbonate and when the coral polyp dies, this skeleton remains incorporated in the reef framework.  Scleractinian corals are in the Phylum Cnidaria, and they receive their nutrient and energy resources in two ways. They use the traditional cnidarian strategy of capturing tiny planktonic organisms with their nematocyst capped tentacles, as well as having a obligate symbiotic relationship with a autotrophic microalgaes known as zooxanthellae.  Zooxanthellae live symbiotically within the coral polyp tissues and assist the coral in nutrient production through photosynthetic activities. These activities provide the coral with fixed carbon compounds for energy, enhance calcification, and mediate elemental nutrient flux. The host coral polyp in return provides its zooxanthellae with a protected environment to live within, and a steady supply of carbon dioxide for its photosynthetic processes.  This symbiotic relationship between polyps and zooxanthellae can be disturbed by anthropogenic impacts including overfishing, increased sedimentation and nutrient overloading.