Coral reefs
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This document summarizes coral reef biology and threats facing coral reef ecosystems. It describes the structure and formation of coral reefs, the requirements for coral growth, and different types of reefs. Corals reproduce both sexually and asexually. While coral reefs support significant biodiversity and provide economic value, they are threatened by overfishing, pollution, coastal development, climate change, and other human impacts. Protecting coral reefs through marine protected areas is important for conserving these fragile ecosystems.
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Coral reefs
- 1. Biology & STATUS oF CoRAl REEFS SUBMITTED TO: DR. S.K.ROUT DEPT. OF AEM SUBMITTED BY: ASIK IKBAL B.F.SC 2ND YEAR FS-06/13 AEM- 216
- 2. What is a “coral reef” ? Biological (“coral community”) Organic, Biogenic Coral and Algal communities Mostly “hermatypic” corals, algae, and other sessile animals Geological features (“reef”) Carbonate In situ build-up Topographic relief Wave resistant Cemented, consolidated
- 3. Corals Class Cnidaria Hermatypic (hard) corals contain symbiotic algae Up to 500 spp. at some sites.Individual animals are called polyps Several polyps make up a colony Corals are closely related to jellyfish and sea anemones—they all contain stinging cells called nematocysts.
- 4. Darwin’s Theory of corals formation Darwin’s theory starts with a volcanic island which becomes extinct. As the island and ocean floor subside, coral growth builds a fringing reef, often including a shallow lagoon between the land and the main reef. As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper lagoon inside. Ultimately, the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon.
- 5. Coral reproduction Corals are capable of both sexual and asexual reproduction. In addition to the splitting of individual polyps, coral colonies can reproduce asexually by fragmentation. This usually occurs as a result of storm damage, when coral colonies can be broken into pieces and the pieces may be scattered. If the coral pieces do not become covered with sand, they may be able to resume growth and form a new colony. This is most common in the branching corals like elkhorn and staghorn corals. All corals are capable of sexual reproduction, although the reproductive strategy varies with species. Some corals are hermaphroditic, where individual polyps contain both male and female reproductive organs. Others are gonochoric, where polyps are either male or female. Some corals release eggs and sperm into the water column and the eggs are fertilized externally—this is called BROADCAST SPAWNING. Other corals keep the eggs inside the polyps and they are fertilized internally and develop into larvae inside the mother polyp. This strategy is referred to as BROODING.
- 7. Building the reef CaCo3 addition - CaCo3 loss = Accumulation Reef-building corals require clear, warm water Shallow areas Most reefs are between 26° N and S latitude There are corals found off Alaska and other cold waters, but they grow very slowly and do not form reefs. Environmental requirements: Physical environment Temperature of 25-31oC (limited Northwards by the 18oC minimum isotherm) Salinity of 34-37 ppt Biological environment Oligotrophic, highly stratified water column
- 8. Types of Coral Reefs Atoll Reef- extends all around a lagoon without a central island. * when an island sinks below the ocean’s surface. Fringing Reef- directly attached to shore. * grow up to the edge of the shore. Barrier Reef- separated from mainland by lagoon. * only grow when there is a change of sea level on the coast adjacent from it. * grow where land is sinking faster in the water.
- 9. A small atoll in the Maldives Inhabited cay in the Maldives
- 10. Coral reef distribution This map shows areas of upwelling in red. Coral reefs are not found in coastal areas where colder and nutrient-rich upwellings occur. Boundary for 20 °C isotherms. Most corals live within this boundary. Note the cooler waters caused by upwelling on the southwest coast of Africa and off the coast of Peru. Location of Coral reef
- 11. Examples The Great Barrier Reef- Queensland, Australia; the largest coral reef system The Belize Barrier Reef- along the coast of Belize down to the Bay Islands of Honduras; second largest coral reef system The Red Sea Coral Reef- coast of Egypt and Saudi Arabia Pulley Ridge- Florida; deepest photosynthetic coral reef The New Caledonia Barrier Reef-length of about 1500km The Great Barrier Reef is on the northeastern coat of Australia The Belize Barrier Reef
- 13. Threats to coral reef systems Overpopulation Bioerosion Unsustainable fisheries Coastal development Global climate change
- 14. Ecosystem effects of fisheries Removal of predators Removal of algal grazers Change in dominance Californian Sea Otters Urchins Crown of Thorns starfish “COTS” (Acanthaster planci) Changes in size frequency of animals
- 15. Terrestrial impacts Pollution Sewage Agriculture Aquaculture Rubbish Sedimentation Eutrophication Construction on reef flats Coral mining Mangrove destruction
- 16. Impacts of tourism Terrestrial development Land reclamation and creation of beaches Mangrove removal Sand on reef flat Boats Anchors Diver/snorkeller impacts and fish feeding Sewage Harbour dredging
- 17. Human impacts on coral reefs Overfishing Sedimentation Nutrient enrichment Chemicals/oil Physical damage (anchors, fishing, groundings)
- 18. Conclusion Coral reefs form some of the world's most productive ecosystems, providing complex and varied marine habitats that support a wide range of other organisms. Coral reefs deliver ecosystem services to tourism, fisheries and coastline protection. Coral reefs protect shorelines by absorbing wave energy, and many small islands would not exist without their reefs to protect them. So in this time the protection of coral reefs is highly importance. Biosphere reserve, marine park, national monument and world heritage status can protect reefs.
- 21. THANK YOU
Notas do Editor
- Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients. Most coral reefs are built from stony, which in turn consist of polyps that cluster in groups. The polyps belong to a group of animals known as Cnidarian, which also includes sea anemones and jellyfish.
- Symbiosis:Many hard and soft corals (and some jellyfish and sea anemones) contain a symbiotic single-celled brown dinoflagellate (algae) called zooxanthellae. This relationship between corals and algae is a type of symbiosis. Both the coral and the algae (known as zooxanthellae) benefit from the partnership, so this is an example of a mutualistic symbiosis. The zooxanthellae are safe from predators inside the coral tissue (remember, corals have stinging cells) and the coral provides them with nutrients in the form of excreted nitrogen and phosphorus. In return, the zooxanthellae provide the coral with sugar compounds that they make when they photosynthesize. Most corals appear brown in color. This is a result of the millions of brown zooxanthellae that are found in their cells. Occasionally, when corals are stresses by high water temperature or other factors, the zooxanthellae will be lost, leaving the corals appearing almost pure white. This phenomenon is known as coral bleaching. The coral may die following bleaching, but often it will recover and become repopulated with zooxanthellae.
- Genetic studies have shown that hermaphroditic corals are capable of self-fertilization as well as cross fertilization (where sperm would come from another coral colony).
- Coral reefs form in tropical areas. Since plants need sunlight in order to make food, reef-building corals can only survive in fairly shallow areas where sunlight can penetrate. Most corals cannot tolerate cold water temperatures; those that can handle the cold do not grow very quickly and do not form reefs.
- Patch reef – common, isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or seagrass Apron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore Bank reef – linear or semicircular shaped-outline, larger than a patch reef Ribbon reef – long, narrow, possibly winding reef, usually associated with an atoll lagoon Table reef – isolated reef, approaching an atoll type, but without a lagoon Habili – reef specific to the Red Sea; does not reach the surface near enough to cause visible surf; may be a hazard to ships (from the Arabic for "unborn") Microatoll – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using radioactive carbon dating and have been used to reconstruct Holocene sea levels[21] Cays – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, forming an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout thePacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land Seamount or guyot – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded and guyots are flat; flat tops of guyots, or tablemounts, are due to erosion by waves, winds, and atmospheric processes
- Coral reefs are estimated to cover 284,300 km2 (109,800 sq mi), just under 0.1% of the oceans' surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%
- Overfishing: Changes trophic structure, Many large predators are no longer present, Grazing fish species are being collected as food fish, May allow algal overgrowth of corals. Nutrient enrichment: Nutrients are elements needed for growth.If there are not enough of certain types of nutrients, they are said to be limiting nutrients Most common limiting nutrients in the marine environment are N and P.