About coral reefs

Coral reefs are large masses of natural structures composed of the skeletal material produced mainly by reef-building (or hard) corals, small organisms that grow in shallow water . Corals are found in both temperate and tropical waters. They leave their exoskeletons when they die and the tide movement slowly layers them to form many types of coral. The corals can only grow within 30 meters (100 feet) of the surface where the temperature is above 16° . Corals are hydroids, in a polyp form . Reefs can only form within approximately 30° of the Equator. A healthy reef normally has a lot of algae, including turf algae, coralline algae, and macro algae. The coral itself does not actually produce the amazing pigments that make it so pleasing to look at. The colour comes from an algae which has a symbiotic relationship with the coral. A symbiotic relationship is when two plants and or animals live with each other and they both benefit from the relationship. The corals provide a safe place for the algae to live, and the algae give the corals food. The algae is called zooxanthellae. Coral reefs support a very diverse variety of marine animal and plant life, the most biodiverse type of marine ecosystem in the world. It takes many years to form a reef, (the average growth rate being a minute 1 mm per year) yet with the new modern threats such as dynamite fishing, it can take a few seconds to destroy one.

Types of Reefs

Fringing Reef

A fringing reef is either bordering a shore, separated by a shallow channel/lagoon, or attached directly to it.

Atoll Reef

Atoll reefs are like circular and continual barrier reefs. They go all the way around a lagoon where a volcanic mountain has collapsed. The highest part of the reef is only barely covered with water. The central lagoon often contains small islands, formed from coral and debris that has been ground to sand by erosion. The biggest atoll reef surrounds a lagoon which is over 97 kilometers (60 miles) long.

Barrier Reef

Barrier reefs are by far the biggest type of reef. The largest barrier reef, the Great Barrier Reef, is over 1,930 kilometers (1,200 miles), and has more intricate landscape than the Grand Canyon. Barrier reefs are found in the Carribean, Belize, and Bahamas.

Types of Coral

Brain Coral

Brain coral is named for it’s likeness in appearance to the human brain. The polyps grow outward, forming an overall shape resembling a boulder. Brain coral is covered with long ridges which are of a different colour than the surrounding surfaces. The whole coral, including the long ridges, is covered in tiny ridges. Each tiny ridge goes halfway across a long ridge or from the center of a area separated by the long ridges to the edge of it, in a radial, sun-like pattern. Brain coral is fairly common.

Pillar/Cathedral Coral

Pillar coral grows in tall pillar shapes which sometimes branch off. This type of coral is very rare. Pillar coral is inhabited mainly by tiny neon fishes. It grows slowly, even compared with other coral, and gets very tall.

Staghorn Coral

Staghorn coral is similar and related to elkhorn coral. It is very delicate, and the tips often break. Staghorn coral does not grow tall like pillar coral, but rather it grows many branches and covers a wider area.

Inhabitants of Coral Reefs

Coral reefs are home to both Chordates and Invertebrates.

Chordates

Chordates (animals with backbones) include:

• Sharks and Rays (Cephalochordata)
• Snakes, Turtles, Crocodiles (Reptilia)
• Marine Birds (Aves)
• Sea Squirts (Urochorda)
• Bony Fish(Osteichthyes)
• Hagfish and Lampreys (Agnatha)
• Dolphins,Whale, Seals, Sea Lions (Mammilia)

Phylum Cephalochordata

Sharks and Rays

Sharks and rays are related to hagfish and bony fish. Their skeleton has no real bones in it, it is made entirely out of cartalidge. Rays and some sharks do not have teeth, instead they use grinding plates to crush their prey. Sharks are the largest fish and have existed for over 400 million years. They are very smart. There are approximately 350 species of sharks, and approximately 425 species of rays. Sharks are generally harmless to humans: only about 5 humans are killed by sharks each year, however many millions of sharks are killed by humans each year. Sharks are endangered by humans and mostly they are only hunted for their fins, and thrown back into the sea still alive, to starve and bleed to death. Human and other sharks are their main predators. Some sharks lay eggs that can take up to to 9 months to hatch, while others give birth to live young. Sharks and rays eat many different things depending on the species, some eat plankton, some fish, some other sharks, etc. Some ray species sting with venom from barbs on their tail and some can produce electric shocks. The fastest shark can go 20 body lengths per second.

Phylum Reptilia

Reptiles

Cold-blooded like all reptiles, these saltwater-dwelling reptiles live in the warm tropical and sub-tropical reefs. They include sea snakes, sea turtles, and crocodiles.

Sea Snakes

Sea snakes are excellent swimmers, equipped with a flat, paddle-like tail and nostrils that close underwater. They have small fangs with extremely toxic venom which quickly kills the fish, eels, and crustaceans they eat. Most of the humans they bite die as well from this potent venom. Many sea snakes have colourful rings around their bodies. The adults can grow up to 2 meters long. Sea snakes are eaten by eagles, sharks, large predatory fish, eels, and, occasionally, crocodiles.

Sea Turtles

Sea turtles are found in oceans all over the world, but are especially common in the warm seas near the Equator. They have a body covered in tough, leathery, protective material and bony plates fused to their spine.They use their powerful paddle-shaped limbs to propel themselves through the warm waters which they inhabit. These turtles get much larger than their relatives, the freshwater turtles, the largest growing up to 2.8 meters in length and weighing about 500 kilograms. The diet of these reptiles changes drastically from species to species. Jellyfish, sponges, mollusks, crustaceans, fish sea urchins, and seaweed are some of the things consumed by sea turtles. They have no teeth, but a sharp beak with a formidable cutting edge is used for these sea creatures’ meals. Their predators are sharks, crocodiles, and mainly humans. The turtles venture onto land only to lay eggs. When the eggs hatch, they must make the dangerous journey down to the sea, and many of them are often eaten by any meat-eaters present, including crabs.

Crocodiles

Crocodiles are large, lizard-like reptiles that live mainly in freshwater. However, there are 2 species that live in reefs. Crocodiles are covered in thick, scaly skin and can live only in warm water. They have long, paddle shaped tails and webbed back feet. Their large, dangerous teeth stick out from their jaws and thus are visible even when their mouths are closed. Crocodiles have great eyesight and hearing which lets them stealthily sneak up on their prey while remaining just below the surface of the water and out of sight. Then using their hind legs, they launch themselves half their body length out of the water and seize their prey. Next they will drown it by holding it underwater on tear it in two by rolling in the water while holding the prey tight in their jaws. The hatchlings eat only crabs, mud skippers, frogs, small fish, and insects. Adults also eat waterfowl, mammals, turtles, and larger fish. The small crocodiles have many predators, but as they reach maturity most of the predators become food. Adult crocodiles are killed by humans, and larger adult crocodiles.

Phylum Osteichthyes

Tropical Fish

Tropical fish include pufferfish, seahorses, stonefish, lionfish, batfish, and many, many other types of fish. They generally are very colourful and they come in a huge variety of shapes. All tropical fish have a flap of bone and skin covering their gills. They all have real bones, not just cartalidge like sharks and rays. Most tropical fish have scales, although there are some that do not. Some tropical fish change colours at different stages in their development. These fish eat just about anything they can find, but often different stages of growth require different diets. The most common type of tropical fish are the butterfly fish.

Phylum Mammilia

Seals and Sea Lions

Seals and sea lions can be found all over the world. They are mammal, so they are warm-blooded and breathe air like we do. They have a streamlined body and thick fur. Seals and sea lions are carnivorous. Their main foods are fish and squid, but they also at krill, penguins, and even other seals. Most seals have large canine teeth for tearing meat. All seals and sea lions are able to go to shore to breed and moult. Young seal pup’s fur is thin and very unlike their parent’s, and they need to stay on the shore until they moult and their fur is replaced by a thick coat that will keep them warm in the water. Also to keep them warm, they have a thick layer of blubber (fat) which acts as insulation. A seal or sea lion can stay underwater for 2 hours, without coming up for a breath. They have large eyes, so they can see very well when they go deep.

Sea Otters

Sea otters are the largest member of the weasel family, and the second smallest marine mammal. They have the thickest fur of any animal on earth, with anywhere from two hundred fifty thousand to one million hairs per square inch (sorry, but if you want that in metric you’ll have to do the math.) Their fur is so thick, that if you put down your thumb on a sea otter pelt, you are pressing down mare hairs than you have on your entire body. The reason for having fur so thick is simple–they do not have the protective layer of blubber found in other marine animals so they use their fur to protect themselves from the chill water. Their fur also is full of air which makes them float and when they swim this is why they leave a trail of bubbles Sea otters eat fish, but their basic diet is made up mostly of shelled mollusks and crustaceans. One of the staple foods of sea otters are sea urchins. This is very useful to their ecosystem because the urchins eat the kelp in the kelp forests and multiply very quickly. Without the sea otters to pick off the spiny echinoderms, kelp forests simply would not exist. Since sea otters eat so many shelled creatures, they have developed a very useful method of cracking those shells. They will dive to the bottom of the kelp bed and find a sharp rock. Then they will drift on their back with the rock on their chest and smash their prey onto the rock until it cracks. If they find a really good rock, they may carry it with them for a while in their armpit and use it many times. Sea otters spent their whole lives in the water–they eat, sleep and reproduce in it because they cannot walk on land. When sea otter mothers need to hunt, they will wrap their babies in seaweed, and since the fur of the pups is full of air, the young sea otters will float around in the kelp bed, away from harm. The predators of sea otters cannot reach them there, because kelp beds are too shallow for whales and the other big mammals which eat sea otters.

Baleen Whales

Dolphins, or Toothed Whales

Phylum Chordata

Spotted Garden Eel

Spotted garden eels are long thin eels, no more than a centimeter thick. They are covered with small black spots. Spotted garden eels have fish-like mouths. They live in colonies and help watch out for eachother. Thier food source is tiny red insects which drift around in the water. The unique feature of garden eels is that they leave most of thier body buried in the fine white sand at the bottom of a reef or lagoon.

Invertebrates

Animals WITHOUT a backbone (invertebrates) include:

• Sponges (Porifera)
• Mollusks(Mollusca)
• Comb Jellies (Ctenophora)
• Corals, Jellyfish, Hydroids (Cnidaria)
• Sea Spiders (Chelicerata)
• Sea Stars, Urchins, and Cucumbers (Echinodermata)
• Crabs, Prawns, and Lobsters (Crustacea)
• Ribbon Worms (Nemertea)
• Acorn Worms (Hemichordata)
• Segmented Worms (Annelida)
• Flat Worms (Platyhelminthes)
• Arrow Worms (Chaetognatha)
• Round Worms (Nemertoda)

Porifera

Sponges

Sponges are believed to be the most primitive of multi-cellular animals, as they have no true tissue or organs. If a sponge is broken down, it simply reassembles itself, being made of loose cells. Sponges come in many different sizes from microscopic to 1 meter. They come in every colour, and many shapes. Sponge larvae drift with the current, and as they reach adulthood they attach themselves to any suitable surface–even other animals. Some sponges bore into coral, shells, and even rocks. They have developed chemical toxins which they use in self defence, but there is one predator who has managed to surpass these defences, nudibranchs (or sea slugs) . These animals are not only immune to the toxins, they can re-use them in their own defence. Sponges feed by using gathering cells lining their internal water canals to filter small particles of food and bacteria out of the water they pump through themselves. These cells then pass the food onto other cells which digest the particles and then the nutrients are passed around the body by specially developed amoeba-like cells.

Mollusca

Nudibranchs

Nudibranchs are sea slugs. The average size of a nudibranch is 22.6 centimeters. Basically they are shaped like slugs, although many nudibranchs have unusual attachments such as frills or tentacle-like blobs. their colouring is extremely varied. From zebra stripes to iridescent white to hot pink edged with orange to glowing purple and blue. Most of these sea slugs are unable to swim, and instead they glide over surfaces with a muscular foot, just like the slugs you would find on land. Some nudibranchs do have adaptations such as long flaps along the bottom of their muscular foot which allow them to swim. Nudibranchs have symmetrical bodies, with two feelers on either side of their head. On their head there is also a mantle, which stores their internal organs and is the part of shelled mollusks that is used to make shells. The outer texture of a sea snail is very varied, just like their colour and appendages. Sea snails can be smooth or rough or spiny or bumpy and lots of other things as well. Nudibranchs are poisonous, from eating poisonous invertebrates, and their brilliant colours warn their predators of that trait. These poisonous invertebrates include sea sponges, which have toxic defence chemicals, and and toxic nematocysts from jellyfish. Most nudibranchs are carnivorous, but some of them are herbivores. Due to their poison, nudibranchs are not a favourite dish among marine predators. The occasional starfish, crab, fish or seabird does eat a nudibranch, but mainly sea slugs have little to worry about. Almost all sea slugs are hermaphrodites, which means they are both male and female, and even so they rarely mate with themselves. Sea slugs do not give birth to live young, they lay eggs. The eggs are generally laid into either jelly or special egg cases for protection, which are attached to something solid. When the eggs hatch, the free-swimming larvae in medusa form (jellyfish-like) swim away. As they develop they will become slug-like and probably lose the ability to swim. Nudibranchs live just about everywhere, in oceans, seas, coral reefs, wetlabs, aquariums, and maybe even your own fish tank. They go just about anywhere where there is saltwater, some sort of shelter, and access to a food source.

Sea Snails

Cnidaria

Reef Building or Hard Corals

Reef building corals are invertebrates. Scientists used to think that when a polyp is in larval (medusa) form, it will simply drift around until it settles on the ocean/sea floor where it starts a new coral reef. It has recently been discovered that polyp larvae can actually swim. At the end of the larval stage they can swim as fast as twenty body lengths per second. All polyp larvae can also sense a reef from kilometers away. Other than the giant ones, polyps can reach a size of 0.5 millimeters. The giant ones, however, can reach a size of up to 0.5 meters. Their growth rate depends what sort of conditions they are in such as the alkalinity of the water and the temperature. Polyps also have a symbiotic relationship with a type of algae referred to as zooxanthellae. this is what gives coral it’s bright pigments. The algae feeds the polyps and the polyps give the algae a nice place to grow, the coral. The zooxanthellae actually live in the tissues of the reef building corals. Polyps are related to sea anemones. During a polyp’s lifetime, it constantly secretes limestone, forming a stone cup-shape at it’s base. Each polyp has it’s own digestive system and organs. A hard coral polyp has six or multiples of six tentacles

Feathers and Sea Fans (Soft Corals)

Soft corals are very colourful, and some even glow under a black light. Unlike with reef building corals, the colour of soft corals comes from the corals themselves. The skeletal structure of a tough but flexible material called gorgonin, which allows the skeletal structure to undulate with the movement of the water around it. The soft coral polyps each have eight tentacles. Another difference between soft and hard polyps is that the polyps share a communal digestive system and all the collected food is evenly divvied out to the entire colony, which acts almost like a single living organism.

Sea fans are flat formations with vein-like ridges running through them. Like other gorgonians, they come int many colours Sea fans grow with their flat face directed against the water’s current so that each polyp is exposed to the maximum amount of food particles.

Plants of Reefs

Sea Grasses

Sea grasses are a vascular plant that is very common in most coral reefs. These grasses are often found in sandy lagoon bottoms. Sea grasses are classified as Angiospermae. Sea grasses consist of rhizomes (or roots), shoots, and leaves. The specialized roots grow along the surface they grow on and their shoots grow vertically. They provide shelter for a multitude of marine life, and among the creatures that dine on them are sea turtles and fish. The plant can regrow itself as long as the rhizome is underground so it is not eaten. Sea grasses pollinate underwater and the seeds are often carried long distances in the current before they finally reach the bottom of the water body they are in to germinate. Sea grasses are autotrophic as well as photosynthetic.

Algae

Coral Reef Locations

This map shows the worldwide locations of coral reefs:

Picture courtesy of Wikimedia.

The Effects of Global Warming

Greenhouse gasses in the atmosphere from pollution let heat from the sun come through, then reflect it back to Earth when it should just bounce out. The result is global warming, the quickly increasing temperature on Earth. The increasing heat melts some of the ice in the arctic, raising the sea level and keeping some countries cooler with the flow of cold water, but overall the Earth’s temperature is increasing fast. The greenhouse gasses also depleat the Ozone layer, the section of the atmosphere which protects us from Ultraviolet Radiation or UV. The increased UV is very destructive to marine life. The water also magnifies the radiation so it is stronger underwater. The animals and plants that are more resistant to this threat live while the others die, thus creating a less diverse, and less stable ecosystem. Another bad thing which global warming causes is called coral bleaching. This is caused when the water temperatures rise, because the algae which feeds the coral can not perform photosynthesis in the wrong conditions.When this happens, chemicals that poison the algae build up. The coral either gets rid of the zooxanthellae to save itself or the toxin buildup in the algae hurts both of them. Whichever way, the coral is bleached and looses it’s brilliant colours, becomes weak and vulnerable to predators, storms, and disease, and is no longer an ideal habitat for the marine life it supports. As well as all of these things, the increased CO₂ (carbon dioxide) in the atmosphere makes the oceans and seas more acidic. These bodies of water are alkaline, and even a slight change in the acidity can unbalance the delicate ecosystems of coral reefs. Polyps (corals) shellfish and other organisms depend on a specific level of calcium that is dissolved in the water for making hard shells for protection. the slight change in acidity decreases the amount of calcium available for these organisms to produce their protective exoskeletons. The deficiency in calcium can even cause the shells of some microscopic creatures to entirely dissolve. The reason that the CO₂ causes the water in reefs to be more acidic is because the world’s seas and oceans, which take up three fourths of the earth, absorb half of the carbon dioxide in the atmosphere like a giant sponge. Only like a sponge, the seas and oceans can only hold so much carbon dioxide, and holding too much also breaks the delicate balance of many marine ecosystems.

Dynamite Fishing and Cyanide Fishing

Dynamite Fishing

Some fishermen use an extremely destructive method of fishing known as dynamite fishing, or blast fishing. This method involves dynamite, grenades, or home-made explosives that are lit and thrown into the water just before denotation. The force of the explosion liquefies the entrails of small fish, some of which then float to the surface where they can be easily collected. Another explosive is normally thrown after the first, to eliminate any large predators interested in the killing of many fish. This method of fishing destroys reefs within seconds and it takes a very long time for them to rebuild, even longer than normal because the blast destroys the habitat of the polyps, and all the living polyps in the area. The reef cannot regrow untill polyp larvae drift from another reef and settle there. Also, most of the fish do not float to the top of the water, but rather sink to the bottom, where they are not used, and therefore decay.

Cyanide Fishing

Another extremely destructive method of catching many fish at once is cyanide fishing. Poison is dumped onto a reef, which lulls the fish so they are slow and sluggish and are simple to capture. The poison settles on the reef and it does not only effect the fish–it kills all the organisms that live there including the polyps, so the reef can no longer grow and be used as shelter for marine life.

Pollution

Some factories dump pollution and trash into water, and it could end up anywhere. Large pieces of junk have hit, sometimes destroying, ships because of that. In fact, there is a floating island of plastic trash in the Pacific that is already twice as big as Texas, and getting bigger. Also, fish eat pollutants which means that the unlucky people who eat the fish eat the pollutants as well. Trash that finds it’s way to coral reefs is very bad for the creatures that live in the coral and for the reef as well, because after a long time it disintegrates and builds up on the coral and then the fish, crabs, etc. that feed on the coral eat it.

Reef Resources

Food Industry

Coral Reefs are a very important source of seafood. They support a very wide variety of edible animals and also plants like seaweed. The edible mollusks, (octopus, squid, and especially sea snails) are highly prized, and even considered delicacies in some cultures. One of the largest threats to coral reefs are destructive methods of fishing and overfishing.

Building

In many villages that border on coral reefs, houses are built entirely from coral. The mortar is generally made from coral, and even the whitewashing is done with coral lime paste. Coral is very good for making cement.

Medical Uses

Medicine cannot be made from hard corals, however some other organisms such as soft corals, sponges, bryozoans, nudibranchs, and pufferfish release chemicals that scare off predators as self defense. These chemicals can be used as antibiotics. There are also some substances that can be extracted from sponges and soft corals which have been discovered to contain anti-viral properties. The coral reefs in Southeast Asia are the habitat of the venom-bearing cone snail. This tiny snail produces a venom that is so potent it can easily paralyse the small fish it feeds on almost instantly. This venom has been used as an anaesthetic for people who are in pain due to severe sickness.

Commercial Use

Shells and coral are collected by divers and sold as souvenirs for tourists. Cowrie shells are the one of the most popular. Sometimes small animals such as seahorses are dried up and also sold as souvenirs. The small and very colourful fish that are not edible are sold in pet stores as aquarium fish.

Tourism

As well as the coral and shells and animals that are sold to tourists, coral reefs are also a popular place for scuba diving.

External Links

Note: they are in order from what looked most informative to least informative, and if you think the order should be different, please say so in the comments.

http://www.reef.edu.au/

http://life.bio.sunysb.edu/marinebio/coralreef.html

http://en.wikipedia.org/wiki/Coral_reefs

http://www.enchantedlearning.com/subjects/ocean/Coralreef.shtml

http://school.discoveryeducation.com/lessonplans/programs/coralreefs/

http://www.uvi.edu/coral.reefer/

http://42explore.com/reef.htm