Ecological features

    Cards (10)

      • The water in tropical seas is often deficient in nutrients so biological productivity may be low
      • however the animals that form coral reefs have inter-species relationships that use nutrients very efficiently and allow a high biomass of life to thrive
      • corals belong to the phylum cnidaria which is made up of over 10,000 species including the jellyfish
    • Coral nutrition -
      • Cilia: these are finger like projections on the coral polyp tentacles which trap planktonic items floating past the polyp which are then passed down to the stomach where they are digested
    • Nematocysts -
      • these are stinging cells that harpoon planktonic organisms floating past the polyp
      • these are then carried by the cilia to the stomach
    • Symbiotic algae -
      • zooxanthellae are photosynthetic algae that live inside coral polyp cells
      • absorb sunlight and provide food energy for themselves and the coral polyps, the polyps and algae have have an efficient method of recycling nutrients
      • carbon dioxide and excretory waste products produced by the polyp are absorbed directly by the algae for photosynthesis and growth
      • the algae produces oxygen and glucose which the coral polyps need ,coral polyps gain over 95% of their food energy from this symbiotic relationship
      • in return the algae have protected habitat and a supply of nutrients
    • Symbiotic algae continued -
      • much of the carbon dioxide produced by the respiration of the polyps is used by the algae for photosynthesis
      • surplus carbon dioxide is incorporated into calcium carbonate that forms coral
      • other wastes from the polyps provide the nutrients needed by the algae which they may not have been able to absorb from the nutrient deficient sea water
    • Reef building corals -
      • many species of corals secrete limestone base which is continually added to, building up into a reef
      • other cnidarians such as sea fans and soft corals do not produce a hard skeleton so they do not add to the reef
      • the physical structure of the reefs also provides many places for animals to live as well as being a rich source of food that supports a complex food web
    • Abiotic conditions -
      • tropical coral reefs are only found where there are very specific abiotic conditions which makes them vulnerable to environmental change
      • Light - the symbiotic algae within coral polyps require bright sunlight. In the tropics there is bright sunlight in shallow water for about 12 hours almost every day
    • Abiotic conditions -
      • Temperature : must be warm and constant in the range of 25-29 degrees
      • Immersion : Polyps must be covered in water almost all the time to prevent them drying out. They cannot live in deep water because not enough light would reach them for algal photosynthesis. Many coral reefs are found where the tidal range is small so they can live near the water surface without being uncovered at low tide
    • Abiotic conditions-
      • Turbidity: the seawater must have very low turbidity. Turbid water reduces light penetration so photosynthesis would be reduced. Suspended solids carried by the water could also settle on the reef, sticking to the cilia and blocking the entrance to the stomach. The survival of coral reefs often relies on mangrove forests and seagrass beds that trap the eroded soil washed off the land and prevent it settling on the reefs
    • Abiotic conditions-
      • Salinity: Coral polyps do not have the ability to regulate water concentrations within their cells. If the salinity of the water changed outside the narrow range of tolerance of the corals the cells would be killed by osmosis with water flowing into or out of the cells