Coral Reefs · 精读课程

① Coral reefs are massive undersea communities that are home to thousands of living organisms.

② A reef can be hundreds of miles long.

③ The "buildings" of this community are made up of many types and shapes of corals.

④ Day and night, thousands of animal inhabitants bustle about, hunting, eating, and avoiding being eaten.

⑤ Almost one-quarter of all the plants and animals in the ocean live around coral reefs.

⑥ That's over 4,000 kinds of fish and 700 kinds of coral that make reefs their home.

① The many corals that form the reefs may appear at first glance to be oddly shaped rocks or spiny plants.

② Corals are actually groups of tiny animals called polyps.

③ Most polyps are very small — between the size of a pinhead and the size of a pea.

④ One branch or mound of coral can have thousands of these tiny, pea-sized polyps attached to it.

⑤ Each polyp has a sac-like body and a mouth that is surrounded by tiny tentacles.

⑥ Polyps are eating machines.

⑦ At night, they extend their tentacles, like arms and hands, to catch tiny animals and nutrients they need.

① There are hundreds of kinds of corals.

② Most of them are divided into two main types: hard, or "stony," corals and soft corals.

③ Stony coral polyps form hard skeletons.

④ When the outer polyps die, their hard skeletons remain.

⑤ Over time, the accumulation of millions of these hard skeletons helps to build a reef.

⑥ Most kinds of stony corals live together with various species of plants called algae.

⑦ The many types of algae help to supply food for the coral and for many of the fish that live around the reef.

① Soft corals grow flexible, woody cores instead of the hard skeletons that stony corals have.

② Soft corals are able to bend with the tides.

③ Some kinds of soft coral are poisonous and will sting if touched.

④ Others, like the sea pen coral, will collapse and hide in the sand if they are approached.

① Corals are often named after what they resemble.

② Stony corals include brain corals, which look like brains, and elkhorn corals, which look like the broad horns of an elk.

③ Soft corals often look like trees or other plants.

④ Soft sea whips and sea pens have long, narrow branches covered with polyps.

⑤ Sea whip polyps are about one quarter-inch long with eight tentacles each.

⑥ The tentacles catch tiny animals and fish.

⑦ Sea fan corals are wide and branching—like a fan.

⑧ Their expansive shape traps bits of plankton to eat as they drift by.

① Most people think of brightly colored fish when they think about coral reefs—and with good reason.

② Thousands of fish, from large sharks to the tiny goby, inhabit reefs.

③ They depend on the reef for food and for protection from becoming food themselves.

④ Some fish live off the algae and plankton around the reef, and some eat other fish that live there.

⑤ A few types of fish even eat the coral itself.

① Crustaceans such as shrimp, lobsters, and crabs also prefer reefs as a favorite eating spot.

② Sea urchins and starfish catch clams and smaller shellfish hidden among the coral branches.

③ Waving sea anemones, which look like graceful flowers, hide in shallow crevices of the reef to wait for their food to drift past.

④ Large holes in the reef make good homes and hiding spots for moray eels.

⑤ No space is wasted on a bustling reef.

① Most reefs are located close to shore in warm tropical waters.

② They can also grow where warm currents flow from the tropics, such as in Florida and southern Japan.

③ Coral grows best in warm water that is between 21 and 29 degrees Celsius (70–85°F).

① Since algae need sunlight to make food, most corals must live near the surface of the water.

② A few colonies of deep, or cold-water, coral have been found at depths from 900 to 1,800 meters (3,000 to 6,000 ft).

③ These individual coral patches don't form long reefs but they do provide shelter for many different types of fish.

④ Since algae cannot grow at depths where light is limited, the deepwater corals feed on other organisms.

① Besides needing the right depth and temperature to thrive, coral reefs are sensitive and cannot survive in many areas because of environmental conditions.

② They do not grow well near the mouths of rivers, where dirt, debris, and freshwater runoff flow into the sea.

③ Fresh water can kill coral.

④ Dirt and debris can cause serious physical damage to reefs.

⑤ Dirt and excess salt can also interfere with corals' food source.

⑥ Reefs can be smothered by dirt or invading plant life.

⑦ Large, violent waves, such as those caused by a tsunami, can even break reefs.

⑧ If a powerful tsunami strikes an area, thousands of years of coral growth can be destroyed in just a few hours by the force of the wave surges.

① As corals are very slow growing, a reef takes a long time to expand its size or to recover from damage.

② Stony corals, such as brain corals, grow the slowest.

③ They add only 5 to 25 millimeters (0.2–1 in) of skeleton per year.

④ Most reefs are between 5,000 and 10,000 years old.

⑤ Some living coral reefs began growing almost 50 million years ago.

① There are three types of coral reefs: fringing reefs, barrier reefs, and atolls.

② Fringing reefs are located close to the shore.

③ They usually follow the natural shoreline, or fringe, of the land.

④ Fringing reefs are common in Hawaii and parts of the Caribbean.

① Barrier reefs have a larger lagoon, or area of water, between the reef and the shore.

② The largest barrier reef in the world is the Great Barrier Reef in Australia.

③ It is 2,000 kilometers (over 1,242 mi) long.

④ It is made up of over 3,000 individual reefs and islands and is home to nearly 2,000 types of fish.

⑤ The Great Barrier Reef is the only living structure large enough to be seen by an astronaut standing on the moon.

⑥ Its oldest sections are millions of years old.

⑦ Most of the modern Great Barrier Reef ranges in age from 6,000 to 500,000 years old.

① An atoll is a type of reef that forms in a circular pattern around a sinking island or an aging island volcano.

② As the island ages and sinks, or as the volcano continues to erupt and break apart, the remaining land eventually disappears beneath the ocean's surface.

③ When that happens, the growing reef forms a circle around a central lagoon.

④ The largest atoll, in the western Pacific, has a lagoon that measures over 97 kilometers (60 mi) across.

① Coral reefs are very fragile, and many things can damage them.

② The two things that cause the most damage are disease and humans.

③ Some conditions, such as white band and black band diseases, are caused by a combination of destructive bacteria.

④ In most cases, the band of bacteria advances up the branch of the coral, destroying the coral polyps and leaving the skeleton behind.

⑤ The skeleton can then be attacked or colonized by other damaging organisms.

⑥ These fast-growing diseases can wipe out an ancient coral reef in weeks.

① Another condition, known as bleaching, occurs when something—usually bacteria—attacks algae, the coral's main source of nutrients.

② Normally, algae live in the tissues of the coral and provide a constant source of food.

③ Their presence even colors the coral polyps.

④ If the coral senses that the algae have become infected, it expels them.

⑤ By losing the algae, the coral polyps lose their main source of food as well as their color.

⑥ They begin to starve, and without their coloration they become transparent, making their skeletons visible.

⑦ The white skeleton makes them look "bleached."

① Most reef scientists believe that a rise in the temperature of the water makes the bacteria grow—and grow faster.

② If the water temperature returns to normal again, the invading bacteria die off and the algae can recover.

③ Sometimes, coral can recover from bleaching.

④ But if the situation that caused the bleaching does not change, the coral, and the reef, will die.

① Humans are responsible for most of the destruction of coral reefs.

② Fishing methods that use poisons and explosives have destroyed over half the reefs in the Philippines.

③ Seaside resorts and homes create soil erosion and polluted freshwater runoff.

④ Fresh water is damaging to coral, and the runoff may also contain chemicals as well as waste material.

① People damage reefs more directly, too.

② Sport boats and commercial ships break off large chunks of reefs.

③ Gas and oil from boat engines seep into the reef habitat, poisoning coral, plant, and fish life.

④ Some sport divers drop their boat anchors directly onto reefs or stand on the fragile coral.

⑤ Others break off pieces of live coral to take home as souvenirs or to sell.

① In addition to being naturally beautiful and appealing as recreational destinations, coral reefs are a valuable natural resource.

② Reefs help shelter our coasts from storms and floods.

③ They are a critical habitat for much of the world's seafood and, as such, contribute to the economies of many countries.

④ Reef plants and animals also provide many important ingredients for medicines.

① Many countries have taken steps to preserve their reefs.

② In Florida and on the Great Barrier Reef in Australia, it is illegal to take fish, plants, or coral from protected areas.

③ Humans and boats are not allowed near many fragile reefs.

④ But this is only a start.

⑤ Only about 3 percent of the world's coral reefs are protected, and many of the laws and guidelines are not consistently enforced.

① Almost a quarter of the world's reefs have already been destroyed.

② Nearly 60 percent are threatened.

③ It is up to all of us to help prevent reef destruction.

④ Even if you don't live near an ocean, your actions can have an effect on the health of coral reefs.

⑤ Be careful not to litter or drop anything in the water.

⑥ Learn what human actions cause an increase in ocean temperatures and the growth of bacteria.

⑦ Conserve water and energy, and recycle as much as you can.

⑧ If everyone does his or her part, coral reefs will remain a beautiful, natural wonder for centuries to come.