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The Undersea Environment of Coral Reefs

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Presentation on theme: "The Undersea Environment of Coral Reefs"— Presentation transcript:

1 The Undersea Environment of Coral Reefs
Coral reefs are the most biologically diverse marine ecosystems on earth, rivaled only by the tropical rainforests. They provide homes and nurseries for almost a million fish and other species. Incredibly, coral reefs occupy only one quarter of one percent of the earth's marine environment, yet they are home to more than a quarter of all known fish species. Let’s take a look at these fascinating communities under the sea that have been in existence for almost 200 million years.

2 Presentation Overview
Biological characteristics of reefs Functions of reefs Potential Diseases and Hazards These are the three important topics we will discuss in this presentation.

3 Coral reefs are like undersea cities.
Communities of coral reefs can be compared to our cities. They are complex ecosystems that rely on the various occupants and the surrounding environment to sustain their vitality. These undersea cities provide food, shelter, and breeding grounds for their inhabitants.

4 Each coral within a reef is similar to an apartment complex in a neighborhood with many tenants
Corals can be compared to a condominium - a home for many different people. A coral reef is simply a community of many of these condominiums, or coral homes. There are many species of coral that grow throughout the world’s oceans, but most all corals have common structural characteristics. Corals have been in existence for nearly 200 million years but reached their current level of diversity only 50 million years ago.

5 A coral is actually a home for billions of tiny soft-bodied animals called coral polyps.
Is a coral an animal or a plant? Many people think that because corals stay stationary on the bottom of the ocean that they are plants. In fact, a coral is actually a home for billions of tiny soft-bodied animals called coral polyps.

6 These polyps reside within a cup-like calcium carbonate skeleton
These polyps reside within a cup-like calcium carbonate skeleton. They have a central opening surrounded by tentacles which can be extended to feed on phytoplankton in the water column. A coral contains a very thin outer layer of living coral polyps. Although most corals contain hundreds or thousands of polyps, some contain only one. The polyp is a hollow, cylindrical animal with a mouth that is surrounded by tentacles armed with stinging cells for capturing food. Underneath these coral polyps is the dead coral skeleton composed of calcium carbonate. Each coral polyp excretes a calcareous exo-skeleton that lives in a symbiotic relationship with zooxanthellae, host algae located in the tissue of the polyp, that gives the coral its green, blue, purple or brown color.

7 There are two different types of corals
Hard Corals known as scleractinians Soft Corals know as gorgonians There are two main types of corals; hard corals composed of stony calcium carbonate, and soft corals made up of a protien/calcium carbonate material. Scleractinians, or hard corals such as brain, star, staghorn, elkhorn and pillar corals have rigid exoskeletons, or corallites, that protect their soft delicate bodies. Gorgonians, or soft corals such as sea fans, sea whips and sea rods, sway with the currents and lack an exoskeleton. Soft coral Hard coral

8 Corals are located in three primary locations
Western North Atlantic Indo-Pacific Coral reefs are located in three primary regions of the world oceans: the Indo-Pacific, the Western North Atlantic, and the Red Sea. These three regions lie between 20N and 20 S of the equator. The Indo- Pacific region stretches from Southeast Asia through Polynesia and Australia, eastward across the Indian Ocean to Africa. This is the largest and richest assemblage of reefs in terms of coral and fish species present. The Western North Atlantic region stretches from Florida to Brazil, and Includes Bermuda, the Bahamas, the Caribbean, Belize and the Gulf of Mexico. The Red Sea is the smallest of the three regions, located between Africa and Saudi Arabia. It is considered a separate region because of the high number of coral reefs found only in this area. Red Sea Indo-Pacific

9 They survive in unique conditions that require...
Adequate sunlight Water temperatures between Celsius Shallow water depths Low siltation In order for corals to live, they require healthy living conditions including adequate sunlight, clean water with low levels of siltation, relatively shallow depths and stable water temperatures. Drastic changes in any of these Conditions for significant periods of time can contribute to the death of corals.

10 Corals obtain food via…..
Zooxanthellae photosynthesis Predation upon zooplankton and phytoplankton Absorption of dissolved organic material Corals obtain their food in three ways. One is through zooxanthellae photosynthesis. Photosynthesis, as you may remember, is the process plants use to convert trapped sunlight energy, water and carbon dioxide into oxygen and carbohydrates (sugar). The zooxanthellae take in carbon dioxide through photosynthesis, and then give off oxygen as a by-product that is used by the host polyp. Both oxygen and carbohydrates are essential elements in the energy production of corals. Algae “leak” these elements into the polyp’s tissue where they are absorbed and used for energy production. Besides playing an important role in coral nutrition, zooxanthellae are also essential in the process of skeleton deposition. The polyp, on the other hand, provides protection for the algae. Corals also obtain their food through more active means. They prey on different types of algae called zooplankton and phytoplankton. These microscopic algae generally float in the water, although some are able to swim short distances, migrating from the bottom of the reef during the day, and back up to the top at night. This is why feeding, for most marine Organisms, is much more active at night. The corals “come alive” at night, eating by extending tentacles to capture their prey. The coral nematocysts sting and immobilize their prey so that the tentacles can withdraw and bring the food down into digestive cavity of the polyp. Polyps can also release mucus in the form of thin sheets over the whole colony or in strands or sheets into the water. Plankton, bacteria and organic debris get stuck to mucus and, the cilia on the tentacles help to bring the mucus back into the digestive cavity. The third way corals obtain food is through the absorption of dissolved organic molecules (DOM), particulate organic material (POM), and from sharing of food. For example, DOM such as glucose and certain amino acids can be absorbed from water through the polyp's body wall by means of tiny fuzzy projections called "microvilli.” These organic molecules enter the water column from decomposing animals and plants. Particulate organic material, such as bacteria, decomposing organic matter and fish fecal material (detritus), are directly ingested by the polyp. Food can also be shared in some species of colonial corals whose digestive cavities are interconnected Thus, food obtained by one polyp can be transported throughout it's own body or to other polyps.

11 Reefs play important roles in the coastal and ocean environment
Habitats for many marine species Breeding grounds for lobster, shrimp, and various fish Food and shelter Barriers protecting the coasts from storms Sources of sand for beaches Recreational areas for snorkelers, divers and fishermen Coral reef ecosystems have important ecological and economic functions for our coastal regions. It is evident that the reef is a significant link to the vitality and sustainability of other environments. Reefs form a natural and self-repairing barrier that protects the coasts by absorbing violent wave impacts of ocean storms and hurricanes. Corals and calcareous algae are major sources of sand. Fish graze on coral and then excrete organic material that contributes to the bottom sediment. Reefs also provide habitat, shelter, food and breeding grounds for many commercially valuable species such as lobsters, shrimp, grouper and snapper. Many regions located close to reefs rely heavily on these fragile ecosystems for their economic stability. Take the Florida Keys for example. This region depends on nearly 2 million tourists visiting the Keys and their coral reefs annually. Tourists come to snorkel, fish, scuba dive and see the sites. Commercial and recreational fishing is another industry that relies on the health of the reefs. The coral reefs support the fish that attract local fisherman, the second-most important economic and traditional force in the Keys.

12 Reefs also clean the surrounding water through sponges that have filtering systems similar to water treatment plants Another function of the reef is to clean and filter surrounding waters. In this way, reefs can be compared to water treatment plants. Filter- feeding sponges, bivalve mollusks, crustaceans, worms, and echinoderms all help to clean the waters surrounding the reef.

13 Many natural and human-induced factors can harm reefs
Bioerosion by fishes and other marine organisms Diseases Storms Overfishing Coastal development Pollution Several frequently observed conditions have been identified as harmful to corals: black band disease (BBD), white band disease (WBD), bioerosion, and coral bleaching. These conditions are all stress-related. However, anthropogenic, or human-caused, stresses can increase a coral's susceptibility to these conditions.

14 Many inhabitants, such as angelfish and parrotfish, utilize the reef as a source of food and shelter. But too much feeding causes bioerosion of the reef. Another condition that can cause coral mortality in the reef is bioerosion. For example, the sea urchin Diadema antillarum functions as both a grazer on algae that can smother coral, and as a bioeroder of corals as it feeds on them. Other bioeroders include crown of thorns, parrot fish, and boring worms. All of these marine organisms manage to weaken the coral structure the coral skeleton, making it more susceptible to breakage during storms.

15 Global warming causes increases in water temperature which can cause harm to the coral reef environment in the form of coral bleaching. Coral bleaching is a symptom of the stress that occurs when water temperatures exceed the coral’s maximum tolerable temperature range. Corals typically grow in warm tropical waters between degrees Fahrenheit. Coral bleaching occurs when sea temperatures rise or when other stresses occur That cause the corals to expel their symbiotic algae.

16 Diseases such as blackband and whiteband disease are caused by excessive warming of waters
Two diseases frequently observed on corals are blackband and whiteband disease. These diseases actually kill coral tissue while advancing in a band around the coral and leaving the white coral skeleton behind. When blackband disease kills part of a colony, the skeleton is then available to be colonized by other coral species recruits. In fact, some scientists suggest that blackband disease may actually help maintain coral diversity because it is most prevalent in coral species that form large colonies. Studies have shown, however, that there were no coral recruits among corals infected by blackband disease after 25 months. It is believed that whiteband disease is caused by a bacterial pathogen not yet known. It affects corals much as blackband disease , leaving behind a white, lifeless coral skeleton. Unlike blackband disease , scientists do not see whiteband disease as being beneficial to reefs. Scientists have shown that whiteband disease destroys the reef structure because algae, invertebrates, gastropods and boring sponges colonize the dead coral skeleton. This colonization works to weaken the coral skeleton,making it more susceptible to breakage during storms.

17 We need to protect our reefs not only for their intrinsic value, but for the economic and recreational resources they provide. Coral reefs deserve protection not only for their intrinsic natural value, but also for the economic benefits - such as tourism, fishing and recreational resources - they provide to tropical areas around the world. If we don't get involved in protecting these fragile ecosystems, the first generation to discover scuba may be the last to enjoy coral reefs.

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