Coral Reef Habitats PDF

1 Coral Reef Habitats & Reef Zones Coral: Plant, Animal, or Rock?  Coral: Plant, Animal, or Rock? Corals are in fact animals Kingdom Animalia Phylum Cnidaria, Class Anthozoa Relatives of jellyfish and sea anemones  Over 800 known species of reef-building coral worl...

1 Coral Reef Habitats & Reef Zones Coral: Plant, Animal, or Rock?  Coral: Plant, Animal, or Rock? Corals are in fact animals Kingdom Animalia Phylum Cnidaria, Class Anthozoa Relatives of jellyfish and sea anemones  Over 800 known species of reef-building coral worldwide Hundreds of species of soft corals and deep-sea corals. (click on link above)  Cover less than 0.015 percent of the ocean Yet coral reefs harbor more than one quarter of the ocean's biodiversity. No other ecosystem occupies such a limited area with more life forms. The ‘rainforest’ of the sea both reef-building corals and the giant trees of a rain forest create a 3-dimensional framework that is home to an incredible assortment of organisms  largest geological features built by organisms  Conditions for Reef Growth 1. Salt water 2. Clear water 3. Shallow water – Needed for zooxanthellae algae  4. Warm water – coral can only grow and reproduce if the water temperature is above 20°C (68°F) ideal 21–29°C (70–85° F). – Water that is too warm is bad for corals … upper temperature limit is around 30-35C (86-90F)  5. Hard-bottom substrate – For larvae to settle and grow 6. availability of food such as plankton 7. Presence of species that help control macroalgae, like urchins and herbivorous fish – To prevent seaweed and other algae from overgrowing the reef Question Why aren’t there extensive reefs on the Northeast coast of South America? Kinds of Coral Reefs 1. Fringing Reefs 2. Barrier Reefs 3. Atolls  1. Fringing Reefs Most common Grow in a narrow band or fringe along the shore Vulnerable to sediment, freshwater runoff, and human disturbance  2. Barrier Reefs Separated from shore by a shallow lagoon Lagoon protected by waves and currents Patch reefs form in lagoon  Ex. Great Barrier Reef 2000 km (1200 miles) along NE coast of Australia Complex system of reefs, lagoons, channels, islands, and sand cays 21 3. Atoll Ring of reef with a steep outer slope and encloses a central, shallow lagoon Tropical Indian and western Pacific Found far from land  Atolls (continued) No river silt and very little runoff Coral flourishes How atolls grow – Starts as fringing reef and builds up on sediment as island sinks – Deep below the lagoon of an atoll, scientists have drilled to find the original volcanic island rock 27 REEF ZONES 1. outer slope - good coral growth 2. buttress zone - heavy pounding of waves smashes all but the densest coral 3. algae ridge - coralline algae withstands wave pounding 4. reef flat - often exposed at low tide, good coral variety 5. leeward islands - densest coral due to lack of waves 29 30 31 Adaptations: Versatility, symbiosis and a variety of niches help reef organisms respond to an unproductive environment. Reefs have no plants. Primary productivity is provided by the zooxanthellae, a dinoflagellate algae that has developed a mutualistic symbiosis within the coral animal. 32 Corals provide protection for the algae. Coral waste products (carbon dioxide, nitrates and phosphate) supply materials for photosynthesis. In return, the algae supplies the food and aids in calcium carbonate secretion of the coral skeleton. 33 Competition is intense for space, light and nutrients. Habitat stratification around the fore reef, flats, forward wall and back reef provide for a variety of populations. Reef fish are brightly colored to identify and attract mates. Sex-changes are common among reef fish to provide enough mating couples. Many are camouflaged to blend in with sponges and sea fans. Some are poisonous and are very aggressive. 34 The nocturnal - diurnal patterns, and natural disasters such as hurricanes also help reduce overcrowding. Some animals, like the crown-of-thorn starfish, parrotfish, cowries and bristle worms, eat coral and pass it through their bodies to form sand. The process is called bioerosion - erosion is caused by living organisms. 35 36