The Great Barrier Reef is one of the most diverse ecosystems in the world. It is home to a plethora of wildlife that includes 400 different species of coral, 1500 species of fish, 4000 species of mollusk and 240 species of bird, all of these serve to enrich this ecosystem as well as to attract millions of people to the reef every year.
The Great Barrier Reef is not simply one reef but a system of smaller ones tightly packed together that stretch for 1200 km from the coast of Poupau New Guinea, to Bundaberg in
Queensland. The reef is fifteen km wide at the narrowest point and has been reported to be twenty-five at the widest point. The reef reaches out to sea at certain points but never into water deeper than a few hundred feet. Coral cannot survive in deep water (Trishan).
The reef is ancient, forming approximately at the end of the last ice age (or the end of the Pleistocene epoch 10,000 years ago) it has since then been a home to the diverse ecosystem that it has come to be intrinsically part of. There is evidence of a far more ancient reef under the present day Great Barrier Reef. "Sea water trapped as ice in enormous glaciers caused the sea levels to fall. Consequently, all previously formed coral reefs probably died from exposure. When the glaciers melted, the sea level rose to its' current position and present day reefs began to develop (Trishan).
As old and constant as the Great Barrier Reef is, it still has more than it's share of problems. The reef has been threatened by invasionary species such as the Crown of Thorns Starfish, that systematically been eating the reef since the seventies. It consumes live corals and destroys acre after acre of reef. Another invasionary species that doesn't seem to care about the damage it does is man. Human activities like farming: creates nutrient and sediment run off, garbage dumping: clogs the reef and kills corals, and simply being careless while visiting the reef have all led to the devastation of the reef (Haynes).
There is hope, however, for the reef. Many things have been done to protect the reef including declaring it a Marine Park in 1979. Australia has also formed the Great Barrier Reef Marine Park Authority (GBRMA) in the hopes of studying and preserving this marvel of nature.
Many scientists have taken up the cause by conducting studies on the reef and what can be done to protect this valuable ecosystem.
STRUCTURE OF THE GREAT BARRIER REEF
Define Coral Reef
A coral reef is a natural barrier made of the bodies of living and dead coral. Normally near the surface of the water it forms usually when a piece of land or large object has submerged. The corals slowly colonize the sunken land or object until a reef base is formed. The corals then begin to grow over time into a coral reef. (Comptons)
There are three types of coral reefs: Fringing, Barrier and Atoll. A fringing reef which is close to land, found mainly in the South Pacific and the Caribbean. A barrier reef which is farther off shore and form when a land mass or large object sinks into relatively shallow water. An atoll is a reef that forms when an island slips beneath the waves and creates a lagoon within itself. Commonly seen the in South Pacific. A ring in the ocean or a horse shoe shaped lagoon forms and corals inhabit it. (Trishan)
Reefs act as a wave break for beaches. The Great Barrier Reef protects the East coast of Australia and serves as a wonderful tourist attraction that helps the economy of Australia (Terrill).
How is it formed?
Reefs are made of coral. However, coral itself is made up of millions of tiny individuals known as polyps. These polyps are a specie of invertebrates. The polyps form together in colonies and cement themselves to the foundation with a special adhesive they secrete from their bodies. Some coral species can grow up to six inches in a year, some take decades to grow that much. Some are centuries old, like the brain coral, some are forming all the time. The corals strain the water that rushes over them, searching for tiny particles of food and keep the water free of debris. This is part of the reason why corals need clean water to live in. They take in the tiny particles of the water and if their are pollutants or chemicals in the water they will die. Corals form over generations. After one generation dies the next generation forms on the dead coral beneath them. Soft corals do not have a skeleton, they simply are a tissue structure of polyps that sway in the tidal breeze. Hard corals have an exterior skeleton made up of Calcium Carbonate (CaCO^3), it helps them to be protected, and it also makes up most of the reef. The reef also sticks together with a little help from some little inhabitants. Creatures like Coralline Algae and encrusting Bryozoans cement the reef together (DISCOVERY).
Reefs are also a great model of efficiency and recycling. Animals like sponges, worms,
bivalves (mussels and clams), parrot fish, and sea urchins break down old and dead corals and return the CaCO^3 skeletons back two the reef and ocean floor in the form of a finely crushed sand (NOVA).
How does it function?
Many corals are active at night and only can be viewed then. The famous colors of coral reefs can be view the best at night with underwater lights because the daylight is filtered by the water and the colors do not show up in the day time. The colors of the corals are do to a special single celled algae that live in their bodies. The algae allow the corals to attach to rock, digest their food, store solar energy and basically are intrinsic to the survival of this species coral. Other corals do not live with partners, they derive nutrients directly from the sea water. Without the algae these coral cannot form limestone skeletons and when they die their is no second generation to grow on top of them (NOVA).
Their are many species of corals that inhabit the Great Barrier Reef. In terms of diversity of coral the reef is not the most diverse. The greater diversity falls to the Indonesian and Philippine reefs. The number of species is still very large for the Great Barrier Reef.
400 different species of corals inhabit the reef. The most common is a Staghorn coral a branching
species. So many corals, it would truly be difficult to identify them but scientists have used a simple system: call them by their appearance. So corals are classified simply by looking at their shape. There are boulder, branching, plate, table, vase, bushy and solitary classes of coral. The only real problem with this naming system is that in calm water certain classes of coral will appear like another somewhere else. (Trishan)
"BARRIER REEF INHABITANTS"
WHAT ARE THEY LIKE?
A day in the life of the Reef
A day in the reef is based on the solar clock. The sun is the driving force in the reef. It begins and ends the day, signals the period of mating, and organizes the shifts of this underwater metropolis (NOVA).
The day begins shortly after dawn. Groupers come out and hunt the twilight hours, fish that will hide for the rest of the day hunt in the dawn and dusk periods, relying on the dim light to hunt. The Lionfish is one of these fish. This species of fish uses venomous spines to protect itself and to herd its prey into a corner where it gobbles it up. A fish associated with the Lionfish is the Pufferfish. The Pufferfish swims along with its larger and more dangerous companion and nibbles at the larger fish's fins and spines. When the Lionfish tries to deter its freeloading companion by eating it, the Puffer quickly inflates in the other fish's throat and is quickly spit out. (DISCOVERY)
As the sun rises the dusk feeders retreat to their day time hiding places and the reef is barren for a little while. Active corals retreat into their limestone skeletons to prevent sunburn. Then, slowly, the reef comes alive. Day time fish become active. They leave their dens and sleeping areas and begin the daily and continual task of eating. These fish are active now because their eyes are finely tuned for color vision, much more than human eyes. Colors are important to these fish and to the reef. Color use advertises species, ability to mate, ability to fight and toxicity. (Discovery)
The day goes on and a curious little fish, known as the Cleaner Raas, busies itself by being the hygienist of other fish. This territorial entrepreneur's job is to eat dead flesh and parasites off of fish that wander into the Raas's territory called a cleaning station. Fish that would normally eat a fish such as the Raas calmly let it do it's work. Fish visit the station regularly because of the "tickling sensation" that the Raas uses to ferret out parasites and the cleaning (NOVA).
Another interesting famous mutualistic relationship is the one between the Clownfish and the Sea Anemone. The Clownfish is brightly colored with orange and white stripes. Its home is actually within the poisonous tentacles of the Anemone. The Clownfish acts as part of the Anemone by behaving like a tentacle and having an immunity to the poison. The fish gains protection from predators and a place to live while the Sea Anemone gains food because the predators of the Clownfish sometimes wander into the poisonous tentacles and are eaten by the fish and his home.
Parrotfish are one of the largest daytime fish and roam the reef in groups. They feed primarily on dead coral on which an algae grows. They are really after the algae so whatever dead coral they do eat is returned to the reef in the form of a finely pulverized sand. The Parrotfish is most interesting at night when it secretes a bag of mucus around it's body for the night. The bag is said to prevent predators from detecting the Parrotfish's scent.
The Goatfish is a quite interesting little fish. Colored blue, black and white, it searches the reef floor with two beard-like protrusions on the bottom of its mouth. It uses them like taste buds and dredges the sand. When it finds something it likes it digs it up and eats it.
The Damsel fish is truly an angry farmer when it comes to food. It claims a space on the reef and then chases fish away from the space. Sometimes it chases fish many times it's own size away. It farms algae. It clears the space long enough for a sufficient supply of algae to form on it and then feasts upon the algae. (NOVA)
As day gives way to dusk so do the day time fish give way to larger and more dangerous fish. The day time fish's eyes no longer work correctly in the dim light so they all find their hiding places and wait for the next day. Reef sharks begin to cruise. Fish like Groupers and Parrotfish school together and attempt to look like a larger animal. They accomplish this with a special sense organ on the sides of their bodies. This is called school mentality. When one fish moves the fish in the immediate vicinity move the exact same way and appear like one animal. Marine Catfish also swarm. They use the same mimicry technique as other fish be they are in competition with one another. The safety of numbers comes with a price: those who are on the inside are the safest but get no food, those on the outside get food but aren't safe. Predator fish, like Jacks and small Barracuda, also school along the reef. For a little while the reef is silent with the tension before the feeding begins. Barracuda hunt for the slower weaker fish while the Jacks like to herd their prey and then rush through the middle when the hunting begins.
Darkness falls and the night-time shift of the reef comes alive. Morey eels peek out of their hiding places. Sharks hunt the fringes of the reef. Certain crustaceans that aren't safe during the day venture out to feed on the coral. Sea turtles continue to eat the kelp in the reef, and the corals become active.
A Gobi and a Blind Shrimp are an interesting pair of room mates. The Gobi is a fish and keeps watch while the Blind Shrimp excavates a burrow for the both of them. (NOVA)
A shift ends for the Cleaner Raas and is replaced by the Harlequin Shrimp. The shrimp takes over the job of the Cleaner Raas for the night. (DISCOVERY)
Fish that are not predators either flee or get eaten. Some simply hide in the sand or run for cover. The Red Grouper uses this confusion to ambush frightened prey.
The predator feeding goes long into the night and continues until the cycle begins the next day. The sun rises and so do the day time fish. (DISCOVERY)
The reef is so dependent upon the sun that the sun even governs when the reproduction of the reef will begin. Once a year triggered by the sun and the phase of the moon, the corals begin the spawn. Each coral begins releasing it's reproductive material in a dance of life and survival. All the material collects in a slick on the surface of the water and are fertilized. Those polyps that are conceived under the light of the moon have to survive the hungry fish below and find a suitable hard surface to land upon (NOVA).
Fish also use these astral queues to initiate their mating. Certain fish fire their sperm and eggs into the water and others simply wait for their mates to come, but in the end the slick that covers the water is thick with the unfertilized material of the entire reef. It is not wasted however, it serves as nourishment for fish who gobble every bite. The slick will rarely last more than a few days (NOVA).
PROBLEMS OF THE
GREAT BARRIER REEF
The Threatened Reef
The Great Barrier Reef is not without its problems. The increasing industry and population of Australia comes with the usual drawbacks of progress: pollution, run-off, over fishing, dumping of garbage and eutrophication all of these are devastating to the reef .
The run-off and the dumping can and does have serious effects to the reef. Fish can become entangled in debris and the run-off leads to the eutrophication of the reef water, subsequently, destroying the coral polyps on which the reef is based. Eutrophication is a process where-by the water in an area becomes increasingly turbid due to sedimentation and nutrient run off. (Haynes)
Not only does the reef have human problems but a little invader also spells disaster for the reef. It is called the Crown of Thorns Starfish. This species is termed invasionary because it has not always been native to the Great Barrier Reef. It consumes corals, eats them right out of their limestone skeletons. This doesn't seem like much of a problem until the fact that this one species of Starfish has eaten acres of the reef for the last twenty years (Trishan). It continues to ravage the reef to this day, but the GBRMA has been hard at work to resolve the problem.
The tourism of the reef is good for Australia and good for humanity to take an interest in this marvel of evolution, however, humans are careless. They break the reef, pollute the water and generally disrupt the delicate balance of the ecosystem.
Many things are being done to protect the reef. The nutrients and particulates that accumulate in the waters of the Great Barrier Reef are a priority of the Australian Institute of Marine Science (Brodie). They are concerning themselves with the water quality of the reef and develop ideas and practices to remedy problems. Overfishing is being controlled by the GBRMA and many regulations have come through to curb this dangerous practice. The dumping of rubbish on beaches and in the ocean was calculated by the Australian Marine Debris Status Review in 1996. This review showed a bleak outlook on the garbage being put into the ocean and onto Australian beaches (Haynes).