A few of our class poses at the sundial at the Lighthouse on San Salvador, Bahamas. See other beautiful phenomena from the Bahamas.
The Coral Reef
The coral reef is one of the most amazing and under appreciated ecosystems to a vacationing visitor. We appreciate its beauty but don’t understand its contribution to our lives. Not only is it beautiful but it is also a city in its own right. However today we have caused much destruction to this ecosystem due to pollutants. The coral reefs give us indicators of survival which we must pay attention to. Our job is now to look at this underwater environment and see what we can do in order to help it help us.
When looking at an ecosystem the word “ecology” has to be included. Ecology is a term meaning the relationship between the habitat, the plants, and the animals that live there. The reef system is one of these ecosystems that will be explored here. The reef system contains a delicate balance between the animals and plants. Once one of these components are effected it changes everything around it. This balance forms an intertwining of a braid. The coral reefs are very complex and form just one part of this braid; the other parts are the mangroves and sea grasses. The knowledge gained from the coral reefs as a part of this braid helps in the total understanding of this underwater ecosystem. Documentations show that in the past mass global extinctions have been preceded by reef collapses. Small animals that lay a stony skeleton of calcium as they grow upward form these reefs. The coral reef is a complete city under the sea.
There are three main types of coral reefs, the fringing, the atolls, and the barrier reefs. These different types are often explained as just different stages of development for the same reef. The fringing reefs grow in shallow warm waters that closely border the coastlines. They are separated from the main land by a shallow body of water. The animal and plant life there will identify the depth and zone of that reef. The reef crest zone breaks the waves, the fore reef zone has medium energy and the groove buttress zone forms rows of corals with sandy passages between the rows. The atolls are island reefs, which form around sinking volcanos. These reefs develop close to the surface separating a central lagoon. There are those that rise from the deep sea and the ones on the continental shelf. These shallow reefs are one of the most productive ecosystems. The barrier reef contains the coral animals that are stationary to the bottom with the plants that move. Those that are windward are battered by wind and waves that cause a grooved architecture. The largest barrier reef is the Great Barrier Reef along Australia.
Corals are made of small animals called polyps with two cell layers, the epidermis and the gasastrodermis with a non-living tissue layer in between called the megogles. These animals put down a calcium base to build up a wall and secrete mucus to help keep the suit away from the coral or it can’t attach. The coral polyps have cilia and a ring of stinging tentacles that will help to sweep the food, or shoot slings to get its food into its mouth as creatures pass by. There is a tissue that stretches over the surface of the coral between the polyps for protection.. These soft-bodied animals use the skeletons as protection and as they grow upward dividing by two leave the stony body behind. They are considered carnivorous, feeding on small particles floating in the water along with the zooxanthellae. The zooxanthellae help in the food production for the polyps. Corals have a symbiotic relationship with zooxanthellae, a living plant dependent on the sunlight to provide the nutrients within the stomach along with CO2. This helps the coral to speed up the building of their stony skeleton by adding calcium carbonate to help in the calcification of the reef so that the waves won’t erode it away Red coral algae grow on top of reef to help protect it from the waves and lie calcium carbonate to fuse and keep the reef together.
There are two main types of reef formation known as the porous skeleton and the solid skeleton. They form better in the warmer water that is clear, shallow, with little silt and not much in seasonal changes. The polyps settle on a firm place where the reef can grow upwards according to the change in the water level. The reef can grow as much as 10 cm. a day with sunlight and less if there is less sun. The reef community will use the energy created through respiration. This digestion of oxygen takes the food and creates carbon dioxide and water. The enzyme, carbonic anhydrase combines with the calcium of seawater and carbon dioxide from plants to make the outer coat to add to the skeleton. The more sunlight the more the plant can help to make the calcium carbonate. Reefs need new larva to continually take over and grow upward or the reef will run down. Atolls are the first place of formation from volcanoes, the larva and coral are moved by the current to land in different places on the outside of the volcano base in shallow water. The calcium carbonate is laid on the floor to form buds to spread out. Once the mountain sinks it leaves behind a lagoon with the ocean side having algae, and the reef with the sand keeps moving out.
There are many types of corals produced in this cycle such as the horn coral, which are low in depth and build skeletons. The hydroid or “fire coral” assume the shape of its support structure. The “mountainous star coral” is the most important reef builder with a column shape that is knobby with large raised cups. Other types are the “pillar coral”, which is like a fuzzy giant finger, the “brain coral” with rounded heads of folds and groves like a brain, the elkhorn coral, with wide flattened branches with raised polyps giving a knobby texture, “leaf coral” looking like lettuce and “finger coral” with large pores, swollen tips and grows thick in colonies. There are so many types of coral and life here that these are only a few.
Corals have many ways in which they can reproduce from asexual, sexual, and budding. Sexually they can do a mass spawning, which allows there to be a better chance of survival, it also leaves a greater chance of producing a hybrid. In this method eggs and sperm are sent to the top of the water to be fertilized. From this a zygote forms into a larva, which will float down and attach to a suitable substrate where it will grow a new colony. There is also brooding where the fertilization happens before they are released and float to the top to settle and also form new colonies. Asexually it reproduces by fragments that are broken off and attach to a new surface where it can begin new colonies. Budding pieces can form from the top or bottom of an old polyp, which will grow into a new colony of coral.
There are many organisms that depend on the reef for life and protection. Many types of sponges live on the reefs varying in color and shape. Sponges are made of two and three types of cells. They consist of holes, which filter the water to gather its food made of many different plankton which make up bulk and with sand help reef build up. Sea anemones a relative of the coral and jelly filled hydroids, are inhabitants of the porous and solid skeleton of the corals. Clown fish is a fish, which is able to live among the deadly sea anemones because of the mucus on the outside that confuse the sea anemone as self. This relationship provides safety for the clown fish and the sea anemone gets the left over food or animals that follow the fish in. Other fish that live among the corals have a unique ability to change their sex. There are some, which stay male or female, their whole life called gonophores. There are those that can change from one sex to another called hermaphrodites. These fish can change for reproduction; however once they have changed they cannot change back. Most will make the change from female to male such as the parrotfishes, gobies, cods, groupers, snappers, and damselfishes. The anemone fish is one that changes from male to female. Then there are the hamlets, which have both male and female reproductive systems so they can switch back and forth to mate as both. Another endangered species is the sea turtle, which goes between the corals and the sea grasses. The turtles use a magnetic field to help navigate between the corals to the open sea. The corals contain many predators with which the turtles must pass through.
There are a variety of animals that inhabit the crevices of the coral reefs. One third of all the fish live among the coral reefs throughout the world. These animals usually do not have to adapt much to weather changes because of the constant weather conditions. Hermit crabs and snails being part of the herbivore community use their shells as hiding places among the color of the coral as camouflage along with the use of purple ink for protection. The sea urchin is another plant eater which helps keep the algae and plant growth down on the reef. It uses sharp teeth for cutting but can also be harmful to coral in that the sharp teeth can also bite off some of the calcium carbonate of the reef. Sea cucumbers can hide and help to break up sand as well as eating the blue green algae. They are dark in color, which helps them to hide. One of their defenses against predators is to release their digestive tract that preoccupies the predator. Pearl fish use the cucumber as protection during the day by going into the cucumber backwards. The mullets are herbivores that ground up the sand that will be deposited at the base of the reefs. Sea club and red lip blenny which have front and back teeth will eat the plants as well as some crabs and clams from the open water and those that live at the coral. They are fast swimmers and rush out to get a bite. Damselfish come in different shapes and colors to match the environment and are very territorial, theyattack intruders and are browsers to help farmer by cleaning out unwanted plants. Surgeonfish travel in schools with a large scalpel at the end of the tail for protection they also eat the algae from the coral. Parrotfish have chopping beaks that grind coral as well as eat the algae. The octopus finds the reef a great hiding place in the caves eating crabs and animals that it can reach with its arms; along with having a hard sharp beak. The moray eel looking like a large land snake will also hide among the corals to attack for its food. Snappers, grunts, and emperors travel in schools for protection eating cucumbers at night. However they make a great meal for the barracuda that preys on the schooling fish with its broad tail to move quickly for a short time. Groupers are very large fish that will feed at dawn and dusk hiding in the coral caves. The top predators of the chain are barracuda, largest groupers, moray eels and sharks. The bottom dwelling sharks are more docile and live among the reef hunting at night. Reef sharks hunt in late afternoon and eat larger fish going deep at night. Diatoms and plankton are plants of the open water. They make great meals as they are pushed by the waves toward the reef. The dinoflagellates of the reef create plant tissue as well as becoming zooxanthellae. Even though the dinoflagellates are helpful to corals in a symbiotic relationship are poisonous to fish and decorate the night waters with flashes of light. Corals are the most abundant plankton catchers where the animals wait at night to make a meal as they brush up against them as the current carries them in. Reef fishes have changed very little over time. Most reef fishes are small, skinny and colorful which helps them hide among the coral. They use their color as camouflage, by changing as warning of danger or as a poisonous fish, such as the batesian who mimics the colors to avoid predators. Some change their color as the water color changes due to the reflection and refraction of the light. The petite butterfly fish within its color has a fake eye near the tail to confuse the predator. Comet fish will hide in caves backwards to look like an eel and anglerfish will combine color and body shape to blend in with the sponges. Some fish have a cleaning symbiosis among the coral heads where larger fish will come to have smaller fish clean fungi, dead skin, and parasites from them with out becoming prey.
Many plants grow among the coral and are known as the producers of the food chain. Photosynthesis is the first level of the chain. They produce the energy, which is stored in sugar. Without plants all life forms would eventually die out. Red and green algae help in the growth of the reef. The halimeda, and sea bottle are plants that help the coral to build up the sand around the plants that grow best among the corals.
Natural environmental changes affect the coral reefs. Global changes in the environment are first reflected in the reef community. The change in water levels such as the lowering of water will leave the reef above the water where they die but leave behind an account of their existence in fossils. Most corals have died out at one time or another due to these changes. Glaciation where the melting caused the water to rise the corals can survive as long as the rise is slow. If it is fast then the coral has less of a chance because it needs shallow, warm water with sunlight to survive. The absence of these reefs also affects our coastlines through erosion, due to waves, hurricanes and tidal waves. Natural forces such as waves can shrink the mountain bases where the coral polyps settle to create new colonies causing an erosion of this ecosystem. However the dying corals can give a new base for new corals to grow closer to the surface. The waves also break down the coral to sand. Another predator is the sea urchins who drill holes into the base of the reef to eat the inside causing the outside to crumble displacing the animal and plant life of this ecosystem. The destruction of these reef communities also affects the inhabitants of the land. Reefs are very fragile and can only tolerate a narrow range of environmental conditions.
Man has become one of the reefs most feared predator. We have caused much of the reefs destruction probably not realizing it at first. Now we have to make changes on our part to help protect this wonderful world below the sea. Some of what we have done is the over development which sends sediment into the water which coats the coral making it unable to survive. The destruction of the mangroves and sea grasses, for mans development, which are a natural buffer for the corals, cause more silt and nutrients to enter the water by changing the water drainage. The extra nutrients also cause algae to grow more rapidly, which will cover and suffocate the coral. This pollutant drainage and sewage also adds to coral diseases that come from bacteria, fungi and viruses that grow more rapidly due to human waste. Some of these diseases are black band disease, coral bleaching where the zooxanthellae leave the coral, discoloring spots, rapid wasting disease, red band disease, white band disease, white plaque disease, white pox disease and yellow blotch/band disease. The movement of the warm current can spread these diseases carrying these diseases with it. Coral mining can cause the left behind corals to die off also by taking the living top part. Anchors from boats break off parts of the coral. Man has also become very over zealous in making of money through over fishing dredging, and explosions. This causes many changes to the food chains in the reef, which disturbs the balance of survival on the reef. The islanders started by providing enough food to feed their families. Now we not only feed our families but also go for the money for bulk fish supplies and big businesses. Over fishing in many ways destroys the balance of fish life in predator prey. Many of these fish also help in maintaining the reefs. However the destruction of the corals also affect the reef fisheries causing more starvation. The removal of different species in the balance of the ecosystem will cause changes elsewhere. For you cannot make a change in one area without it affecting many others.
There are other habitats that help to balance the ecosystem of the corals which when destroyed cause more danger to this underwater wonderland. The mangroves are the closest to the land and help to filter pollutants and sediment from entering the ocean reefs. There are three types of mangroves. The red mangroves trees are the farthest from land and tolerate the most salt by using reverse osmosis to keep salt out of the roots. They transfer the salt to the leaves. The black mangroves are closer and also remove the salt through their leaves through special pores that the Indians used by scraping the leaves as food. White mangroves are the closest to the land with the least amount of salt, which is removed form the base of the leaves. These trees live in hydrogen sulfide muck that is low in oxygen. The get their oxygen from projections that surround the trees by sticking out of the water. These mangroves also receive the most pollution and sediment. The mangroves absorb the nutrients that are passed along to the sea grasses and corals. The sea grasses closest to the corals help to filter the nutrients after the mangroves from the land. The mangroves and sea grass help in keeping the nitrogen and phosphorus from creating algae blooms that will destroy the coral reefs. The herbivore fish also add to the reefs immune system by helping to remove the algae from the coral.
This has looked generally on the parts of this underwater city. The many braids that are woven in this environment are all connected. Once one is changed it changes aspects of the rest. Now we have to make changes on our part to help protect this wonderful world below the sea. The question now is what can be done to help save this marvelous city which in turn may save us.
Alan Emery, The Coral Reef. Ontario,CBS Broadcasting Corporation, 1981
Osha Gray Davidson, The Enchanted Braid. New York, John Wiley & Sons,Inc., 1998
David Alderton, Fiona Campbell, Charlotte Evans, Don Harper, Nigel Henbest, Tony Juniper, Mark Oakley, Dene Schofield, The Ladybird Discovery Encyclopedia of the Natural World. London,UK, Ladybird Books, 1998
Joseph D. Exline, Ed.D., Jay M. Pasachoff, Ph.D., Barbara Brooks Simmons, Carole Garbuny Vogel, Thomas R. Wellnitz, Prentice Hall Earth Science. New Jersey, Pearson Education, Inc., 2002
Dr. Frank H. Talbot, Under the Sea. Australia, Weldon Owen Pty Limited, 1997
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