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Great Barrier Reef
This show conforms to the following state science standards: 12.B
Coral reefs are among the most productive communities of organisms on earth.
The efforts of countless numbers of individual coral animals, called polyps, add
to the work of many other members of the reef community to form important
topographic features of the earth. Some of these, like the Great Barrier
Reef, which extends some 2,000 kilometers along the eastern Australian coast,
are large enough even to be visible from space. That represents a lot of
work, and it has obviously taken a great deal of energy to accomplish.
Indeed, reefs are scattered over almost 200 million square kilometers of the earth's tropical surface, far more area than any of the other high-producers such as sugarcane fields or marine grass beds. They take high honors in overall productive work.
The coral reef community conserves about half of the 24 grams of new organic material it produces each day for every square meter of its surface. The other half is used up as food for the growth and work by the coral animals themselves and the myriad other organisms that inhabit the reef environment. Although corals are the dominant builders, they are far from being alone in contributing to the net gain of material in the reef. There are a number of calcareous algae which produce carbonate deposits and many other animals such as clams, mussels, and snails contribute their hard carbonate shells to the accumulation limestone of the reef.
Growth and Breakdown
Of course, as reef material accumulates, there are members of the community that live by consuming it. A number of worms, mussels, sponges, and sea cucumbers dissolve or bore their way into the solid reef material for food, support and refuge. Other animals such as starfish, urchins, and fish may feed directly on the living coral. Parrotfish, for example, use their strong beak-like jaws to break off pieces of coral with such vigor that and attentive swimmer can hear the crunch. And of course waves and storms and even lava flows from volcanic islands take a real, if erratic, toll of reef growth.
Thus, simple maintenance of a reef requires the production of new material at a rate at least sufficient to keep pace with the destruction of older parts. These dynamic features of growth and breakdown result, ultimately, in the accumulation of 'processed' carbonate sediments which then gradually consolidate into coralline rock platforms. Such platforms support the living reef.
Growth slow but fruitful
The growth of individual corals is not particularly impressive. Although it is difficult to measure and varies widely from place to place and from one variety of coral to another, it is estimated to be less than three or four centimeters per year at best. This means that, under ideal conditions, a fully submerged reef may approach the surface at little more than two centimeters per year. Or, put another way, it would take a thousand years to build up twenty or so meters of reef. Still, in a healthy reef this rate of productivity is sufficient to maintain the community to the extent that is can serve as a continually renewing barrier against the sea and thus protect oceanic islands.
The total amount of material which is produced and conserved on a reef is very high. But from microbes to sharks, the interacting diversity of living creatures which ultimately depend on the productivity of the reef is overwhelming. No other habitat on earth compares to the coral reef in the abundance of individuals and number of species. The richest of coral reef faunas, in the Indo Pacific, includes about 700 different species of multicellular animals. Even the poorest of reefs of the Atlantic compromise perhaps fifty different species, not including the fish.
The Key: Symbiosis
The secret of support of the density, diversity, and productivity of the reef lies in an interesting symbiotic relationship between the hard-working coral animals and vast numbers of very tiny, single-cell algae called zooxanthellae. These fascinating little organisms, which are photosynthetic, live inside the coral's own cells. Just as in a balanced aquarium where the plants and animals benefit one another, the zooxanthellae and coral provide for many of each other's needs.
Although they are handicapped without them, corals do not require zooxanthellae for life. Corals are carnivorous little animals which feed on minute floating animals that they capture by means of small stinging cells on their tentacles. But corals cannot derive enough energy from this source alone to do much more than just maintain themselves. They certainly can't do the work necessary to build a reef.
Their efficiency is greatly increased however, by the presence of the zooxanthellae in their tissues. Nowhere do reef-building corals exist without this relationship. But the corals do not consume the zooxanthellae directly as food; the relationship between the two organisms is much more refined than that.
First, from the coral the zooxanthellae obviously derive support and protective shelter. But more importantly, they also receive a constant supply of certain critical nutrients, primarily nitrate and phosphate, which are waste products of the coral's own metabolism. Having an internal 'sink' for these products saves the coral energy in not having to excrete them which it would otherwise have to do because they become toxic as they accumulate.
But the primary nutrient that the coral supplies to the zooxanthellae is carbon dioxide, another of its metabolic wastes. The algae, through photosynthesis, uses sunlight to assemble three molecules of carbon dioxide with an equal amount of water to produce glycerol, a very handy energy source for both the plant's and the coral's metabolism. As a extra bonus, the plant also liberates oxygen directly into the coral's tissues and this appears to be stimulating to the coral - a little like a metabolic accelerator.
So the internal production of food and fuel, the oxygen necessary to burn it to do work, and the energy savings of built-in waste removal allows the corals to do the impressive work we see as the primary productivity of the reef. That work finally results in the construction of the massive skeletal platforms of the reefs themselves.
Tiny but plentiful plants
Zooxanthellae are so numerous in the tissues of the corals that they are responsible for the brownish-green color of most coral flesh. Some corals produce pigments of their own, but most are colored by their little, internal, photosynthetic 'roomers.' When the coral animals reproduce by budding, some of the zooxanthellae are contributed sexually, the developing embryo receives its infusion of zooxanthellae from the maternal tissue before the larva is released.
There are certainly plenty of zooxanthellae to go around; it has been estimated that there are tens of thousands of them in each individual coral polyp. The zooxanthellae, on the other hand, reproduce only within the coral tissue and cannot live outside of it. In addition to the zooxanthellae, there are even greater numbers of other photosynthetic algae associated with the external skeleton of corals and these also contribute to the health and well being of the coral.
The symbiotic relationship of the zooxanthellae and the corals also accounts in part for the distribution of coral reefs on the earth. Although reef-building corals do require the warmer waters of the western tropical oceans, this factor alone does not allow such corals to thrive. They also require appropriate exposure to sunlight upon which their resident zooxanthellae depend. This means that reefs cannot grow in water too deep fro sunlight to penetrate, or in water in which there is so much suspended material that the bottom-dwellers are shaded or covered with sediment.
Corals may be able to live in the dark, and many types of corals do, notably the rare and precious black, pink, golden, and bamboo corals used in jewelry. But those corals which build reefs occur only in warm, clear, sunlit waters. And all of the exotic animals which comprise the reef community, whether feather-duster worms, basket stars, or sharks feeding on smaller reef fish, ultimately depend for their food, shelter, indeed their very existence, on the tiny little plants with the long, long names.
THE GREAT BARRIER REEF
Threats to the existence of ecosystem of Barrier Reef ecosystem of Minnesota
Over fishing
Urban sprawl
Souvenir hunting
Forest fires
Shipwrecks
Waste-dump contamination
Fertilizers, pesticides, herbicides Acid rain
Silt
Nuclear power plant waste
Mining
Taconite wastes in Lake Superior
Oil drilling
Industrial air pollution
Oil spills
Oil spills in Mississippi River
Vocabulary
Bommie - from the Australian Aboriginal word, bombora, or
submerged rock
Carnivorous - flesh-eating
Cay - a small, low islet composed largely of coral or sand
Colonial - grouping of the same kind of animals of plants
living or growing together
Crustacean - any of various predominantly aquatic
arthropods of the class Crustacea, including lobsters, crabs, shrimp, and
barnacles, having a segmented body, a chitinous exoskeleton, and paired, jointed
limbs
Decimated - destroyed or killed a large part of
Ecosystem - an ecological community together with its
physical environment, considered as a unit
Habitat - the place or site where a plant or animal
naturally or normally lives and grows
Herbicides - agents used to destroy or inhibit plant
growth
Plankton - plant and animal organisms, generally microscopic,
that float or drift in great numbers in fresh or salt water
Predator - an animal that lives by preying upon
others
Scavenging - feeding on dead animal flesh or other
decaying organic matter
Sedentary - attached to a surface and not free-moving, as
a barnacle
Symbiotic - a kind of relationship in which two or more
different organisms are in a close association that may be of benefit to each
Tectonic - pertaining to, causing, or resulting from
structural deformation in the earth?s crust
Tentacle - an elongated, flexible, unsegmented
protrusion, such as one of those surrounding the moth or oral cavity of the
hydra, sea anemone, or squid
Viscous - having relatively high resistance to
flow; gluey
Zooxanthellae - Minute yellow-brown algae
which live and reproduce within the coral polyp?s cells
Live on Boulder Coral
A few concepts in the film
ecosystem
scientists' questions and reasons for studying the Reef:
Animals (and two plants) in approximate order of appearance
Australian aborigines
Scientists
Divers
Australian city-dwellers
Coral (350 of the 700 species of coral live in the Reef)
Specific types
mentioned:
Plate
Staghorn
Mushroom
Fan
Table
Brain
Boulder
Crinoids ("animals which look like plants")
Wobbegong Shark ("sharks which resemble encrusted coral")
Butterfly Cod ("fish like butterflies")
Toadfish ("like blimps")
Plankton (Food for coral and other animals)
Symbiotic relationship
Giant Anemone (Poisonous)
Clown Fish (Protected from anemone by mucous coat
Zooxanthellae (Symbiotic with coral)
Reputations are worse than reality
1. What does it look like?
2. How big is it?
3. Where does it live?
4. What does it eat?
5. How does it protect itself?
6. How does it reproduce?
7. How long does it live?
8. Do humans use it? How?
9. Is it endangered?
10. Is it protected by law?
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