Corals and coral reefs

Transcription

1 10 Corals and What you will learn A tiny polyp protecting a giant Increasing in number Formation of reefs Organisms Adaptation to the environment Threats to Endangered organisms 101

2 Corals and 10a A tiny polyp protecting a giant Have you seen a coral polyp? Is it an animal or a plant? A coral polyp is a tubular saclike animal. It has a mouth in the centre. The mouth is surrounded by finger like structures called tentacles. The tentacles are used for defense and for catching food. The polyp cannot move from place to place as it is attached. Polyps: in the daytime Reef building corals produce an outside skeletal cup of calcium carbonate. This skeletal cup protects the polyp. During daytime when the polyps are not feeding the tentacles will be withdrawn into the skeletal cup. At night, they extend their tentacles to capture food. Polyps: at night Inside the tissues of the polyp microscopic algae are found which make the corals appear in different colours. The algae provides food and oxygen for the coral polyps and in return the coral polyps provide protection and access to the light. Do you Know? Corals are included in the same group as jellyfish and sea anemones. 102

3 Coral shapes Shape of corals vary enormously. There are four main forms. Branched coral Eg: Staghorn coral Foliaceous Eg. Lettuce leaf coral Solitary coral Eg. Mushroom corals Massive coral Eg. Brain coral K Ideas!Coral is an animal which has a mouth surrounded by tentacles.? 1 What is a coral polyp? 2 What is the use of the skeletal cup of corals? 3 What is the use of algae that lives inside coral? 4 Why do you think the corals are in different shapes and sizes?!inside the coral tissue lives an algae which is able to make food.!there are four main types of corals which are massive, branched, foliaceous and solitary corals. 103

4 Corals and 10b Increasing in number There are two types of reproduction in corals. Sexual and asexual reproduction. Sexual reproduction involves joining of male and female eggs. In asexual reproduction, the corals may increase in number by budding. Budding occurs when a portion of the parent polyp pinches off to form a new individual.!! Do you Know? Corals are triggered to release millions of sperm or eggs by the phase of the moon on a particular night. This is known as mass spawning. 104

5 Conditions necessary for coral growth Warm water Corals of tropical reefs have a temperature range of º C. Their most favourable temperarture is about 28 º C. Water movement Corals need water movements to remove sand and waste material and to bring fresh supplies of food and oxygen. Moving water also keeps the salt content the same. Light Corals need light to grow. The algae that lives inside the corals need sunlight for photosynthesis (make food). Substrate Corals need a firm surface (substrate) to attach themselves and grow. Clear water Unclear water will slow or stop the growth of coral. Dirt, silt and other things in the water will cover the polyp s mouth and prevent it getting oxygen and food. Dirty water will also stop light from reaching the algae that lives inside corals. Salty water Corals will grow when there is just the right amount of salt in the water. If the water is too salty corals will not grow.? 1 What are the two types of reproduction in corals? 2 Why do corals need clear water to grow? 3 What is the ideal temperature range for corals to grow? 4 Why do corals need light? K Ideas!Corals reproduce sexually and asexually.!corals need warm water, clear water, a suitable substrate, salty water, water movement and light to grow. 5 Write a brief essay on the life as a coral polyp. 105

6 Corals and 10c Formation of reefs Coral reefs are found in most tropical areas. Reef building corals secrete calcium carbonate which acts like a cement. These bind together coral, sand and pieces of rubble to form a more solid structure known as the reef. Types of reefs There are three main types of reefs. Fringing reefs - they grow in shallow water from the shoreline to about half a kilometre offshore. Barrier reef - they are found along the edge of continental shelves. The distance from tne reef to the land may range from 0.5 km to 5 km. Do you Know? Islands range in size from very small mud and sand islands of only a few square metres, to Greenland, which has an area of 2,175,600 km 2. Atolls- They are ring shaped reefs found in the middle of the ocean. 106 The word atoll is derived from atholhu a native name in Maldives.

7 Darwin s volcanic theory The modern theory of coral atoll formation was originated by Charles Darwin Slowly the island starts to sink and the belt of corals becomes more wider and more compact. 1 An atoll originates from fringing reefs surrounding the coast of a volcanic island The island, now almost disappeared, is surrounded by a ring of corals. 4 The island has disappeared. The belt of corals is fully developed. 5 The combined effects of the currents, waves and tides plus the growth of the corals changes the emerged part of the atoll which may rise some meters above the surface forming- sometimes large islands. 5 K Ideas!Three main types of reefs are fringing, barrier and atoll reefs.? 1 In which part of the world are found? 2 What are the main types of reefs? What type of reefs do you think are found in Maldives? 3 Make a poster with diagrams showing how atolls are formed according to Darwin s volcanic theory.!according to Darwin atolls formed when volcanic islands sank as reefs started growing around the island.as the volcanic island completely sink a central lagoon remained surrounded by the reefs which eventually turned into islands. 107

8 Corals and 10d Organisms Coral reef is the home for many organisms like worms, shrimps, crabs, lobsters, sea anemones, sea urchins, octopuses, squids, clams, skates, some sharks and turtles. Many organisms living amongst the reef are brightly coloured. Reef Special body colourings are used by the animals to blend into the colour of their surrounding environment so that they can avoid predators. Sometimes body markings on dangerous organisms act as a warning to others. These markings may be mimicked by other animals as a form of protection from potential predators. These are some organisms found in reef environment. Star fish Parrot fish Sea anemone Moray eel Lobster Giant clam Do you Know? 108 Green sea turtle The world s smallest fish is the marine dwarf goby which has an average length of 8.6mm. The largest fish is the whale shark, with specimens recorded at 12.65m.

9 Lagoon Unlike the reef, fish that live in the lagoon are not very brightly coloured. Organisms that can burrow in the sand like sting rays and sea cucumbers are found in the lagoon. Sea cucumber Sand eel Goby Deep sea Fast moving migratory fish are found in the deep sea. Fish like tuna and shark are generally coloured dark on top and light underneath. These colours merge with the dark seabed when viewed from above and the light sky when viewed from below. Sting ray Shark Tuna K Ideas!Coral reefs are home to many different organisms.? 1 Why do you think that the life forms in coral reef environment are so brightly coloured? 2 Name some organisms that are found in the reef other than the ones mentioned here?!many organisms have colours which are similar to the environment they live in. 109

10 Corals and 10e Adaptation to the environment All living things are adapted to their environment. They fit in where they live. Sometimes the environment changes and the animal has to change with it. Camouflage The stone fish is well camouflaged, looking very much like a weed covered stone. A stone fish in coral rubble is especially difficult to recognise. Many butterfly fish and angel fish are striped and flat. The contrasting lines help them to hide in branching corals. Flat fishes like flounders are able to lie on their sides and change the upper surface colouring to match the sand they are lying on. Octopuses avoid detection by predators by changing colour quickly. They use their tentacles for walking and they are also excellent swimmers. 110 Do you Know? The eyes of an octopus can adapt to rapid changes in the amount of light available as it moves quickly from the depths of the ocean to near the surface.

11 Other adaptations Trigger fish have dorsal spine which can be locked into an upright position. It is used to lock the triggerfish into coral cavities so that predators cannot pull them out. Most sea slugs are brightly coloured and patterned. These features suggest that it is poisonous or dangerous and should be left alone. Puffer fish or porcupine fish can puff themselves up to look twice as big. Sting rays have poison-tipped sting which is used as defence if something stands on it and is also used to attack other rays when fighting for a mate.? 1 How does the following organisms camouflage themselves? a. Butterfly fish b. Flat fish c. Stone fish 2 What is the use of the dorsal spine in trigger fish? 3 Find out about other marine organisms not mentioned in the text that can camouflage and that have special features that they use as protection. Make a poster about these organisms. K Ideas!Living things are adapted to their environment.!animals camouflage themselves to stay alive.!some animals have special features which are used to protect themselves. 111

12 Corals and 10f Threats to There are both natural and human destructions to corals. Naturally corals are eaten by crown-of-thorn starfish, coral eating fishes like parrot fish and boring organisms like tube worms. Crown of thorns Tube worm Parrot fish When natural disturbances like cyclones, hurricanes, actions of earthquakes and volcanoes are not frequent, reefs can recover. However, human activities tend to create widespread and long term disturbances. Human threats Trash dumped into the water can kill the coral reef and the organisms that live there. Garbage at the seaside often ends up in the sea and disrupts the coral reef s delicate environment. Careless boating, diving, fishing, and other recreational uses of coral reef areas can cause damage to. 112 Do you Know? Fishing with dynamite, cyanide, or bleach has killed many especially in the Indo-Pacific region.

13 Dredging to make harbours covers the corals with sand. Mining corals for building purposes kills the whole reef area where mining occured. In Maldives mining cannot be carried out on house reefs. Dredging Mined corals Due to overfishing, reef fish population greatly decreases in number. The removal of large number of reef fish causes disturbance to their natural environment.? 1 What are the organisms that destroys corals? 2 List other ways that are not mentioned in the text of how human activities can destroy? 3 Imagine you live on an island and you need to protect the reef environment. Discuss the ways that you can protect the reef environment. Ideas K! Corals are destroyed naturally as well as by human activities.!corals are threatened by marine pollution, overfishing, dredging, anchoring, trampeling, coral mining and collection. 113

14 Corals and 10g Endangered organisms Endangered organisms are those in danger of disappearing from the face of the earth if its situation is not improved. When its race has not been seen in the wild for over fifty years, we say that it is extinct. Those organisms that may soon become endangered are called threatened species. Blue whale What causes extinction? Extinction has been occuring naturally for million of years and it continues to do so today. The current problem is that organisms are becoming extinct because of humans. One reason is that there are more people on the earth every day and they kill organisms for food and sometimes for fun. Another way humans endanger animals is by changing the environment. Also extinction can come from pollution such as oil spills and waste. Here are some marine organisms that are endangered in Maldives. Can you think of ways to save them? Napolean wrasse Giant clam Turtles Black coral Sea cucumber Do you Know? Oyster whale shark Blue whale is the largest ever mammal. There are about 500 individuals today in the southern hemisphere, down from an estimated 250,

15 Endangered marine organisms in the world Coral Green sea turtle (velaa) Bottlenose dolphin Logger head turle (boabodu velaa) Humpback whale Great white shark? Mako shark 1 What are endangered organisms? 2 Why do you think these organisms are endangered? What are the threats to them? 3 Make a poster showing endangered marine organisms of Maldives. 4 Discuss how you can protect endangered species. Ideas K!Endangered organisms are those that are in danger of extinction.!in Maldives some endangered marine organisms are: a whale shark b mother -of-pearl c giant clams d black coral e turtles 115

16 Corals and SIR JOHN MURRA URRAY ( ) Born in Canada of Scottish descent, Murray came to Scotland to be educated and eventually entered Edinburgh University, to study medicine. Instead he joined a whaler as surgeon for a seven month voyage to the Arctic. Murray is noted today, and particularly in the USA, as the founder of modern oceanography. He studied ocean basins, deep-sea deposits, and coral-reef formation. As a marine scientist, he took part in the Challenger Expedition ( ), the first major ocean graphic expedition of the world. He was first to observe the Mid-Atlantic Ridge and the existence of marine trenches. He attempted with Buchan to construct from temperature and salinity observations a qualitative theory of water movement in the world s oceans. With A. Agassiz, he put forward a modified hypothesis for coral reef development, arguing against Darwin s hypothesis and suggesting that subsidence was not always a controlling mechanism. He died in 1914, killed by a motor car. 116