The basis of life in the sea

part I

About a hundred years ago, scientists in their search for further understanding of life in the sea first used fine nets and found sometimes many and sometimes few small floating animals and plants drifting in the water at the mercy of the currents and winds that drive them. As finer nets were used or alternatively as more refined methods of collection were devised, the plants were found to outnumber the animals vastly. Almost all the microscopic and unicellular material was proved to be of plant origin and we today cannot be surprised to hear that they were limited to the uppermost layers, where alone light is adequate for plant growth; although the small animals caught with such nets might be found at almost any depth.

These minute plants and animals are collectively termed the plankton, because of their drifting life. This is not a systematic unit, but a convenient grouping of organisms according to their mode of life. Representatives of nearly every main type of animal from fish to Protozoa are found in zooplankton, some being planktonic all their lives, and others like the young of crabs and mussels and the baby fish, being planktonic only their earliest life. After this they settle on to the bottom or grow into fish that are strong enough to stem the currents. All derive their nourishment, often directly, from the microscopic plants or phytoplankton.

Compared with animal plankton, the plants are relatively poor specialized and comprise only a few groups of algae, of which diatoms and flagellates are the best known. They have many relatives on land and in the fresh water but their numbers are incalculably greater in the sea. Even the numbers to be caught in a small net may run into many millions, while despite their individual minute size at times they may be sufficiently abundant to color the water. Further unlike those animals and plants which live for a year or more, these unicellular plants can reproduce so fast that the number caught at any one time may give only a slight idea of the total top that a particular volume of water may be providing.

During their flowering, almost as large quantities may be produced and eaten daily by the animals as can be caught in the net at any moment.

part II

The grass of the sea. Upon it as far we know almost all other forms depend, including the commercial fishes, altogether these form only a small fraction of the animals in the sea. The abundance of the plants varies from season to season. They depend not only on the light and dissolve carbon dioxide but also on the varying quantities of nutrient salts. In the deeper waters these nutrient salts are more or less uniformly distributed, but in the surface layers of temperature latitudes they may be quickly reduced by plant growth; and if they are not speedily replenished, growth slows or even ceases until water movements bring some of the deeper supplies towards the surface once more. This overturn can occur seasonally at the times of autumn and winter storms, but in some regions there is an intermittent or even constant upwelling of deep and usually fertile water, which maintains there a denser phytoplankton that elsewhere. In one way or the other the shallow seas and oceanic banks are region, which are fairly regularly bathed by nutrient-rich water and it is no coincidence that it is on such banks that our great fisheries have been founded. They are the indirect result of these rich supplies of the nutrients, and of the amazing power of the plants to concentrate and combine them into proteins and oils and resembling those of land plants as well as minute quantities of complex compound vitamins, antibiotics, and so on, which are also typical of plants.

For a truly remarkable thing about the plants is their power of concentrating the nutrients they need. Relative to seawater they concentrate carbon, phosphorus and nitrogen. Then in turn the animal plankton and the bottom animals sift the basic plant food from the water and concentrate these animals further.

Thus the route from plant to fish is not necessarily direct, although for the herring and its relatives it is nearly so. The plant plankton and the greater part of the herring’s food consist just of such small plankton animals. For all its size, the whale feeds directly on animal plankton, as does the shark. So rich is its food in the Antarctic that in two years the blue whale can grow to a length of 60 feet and a weight of 50 tons of plankton alone and reach 200 or 300 tons when fully grown.

PART III. TEXTS FOR READING AND DISCUSSING.

WILD AMERICA The Grand Canyon

Probably you have seen photographs of the Grand Canyon, the great valley in the desert country of Arizona. But you must go there yourself to feel its true size and beauty. The Grand Canyon is one of the greatest natural wonders of the world.

The Colorado River formed the Grand Canyon over millions of years. Slowly, the river cut down through hard rock. At the same time, the land was rising. Today, the canyon is one mile deep and 277 miles long. The oldest rocks at the bottom of the canyon are more than a billion years old. The width varies from six hundred feet to eighteen miles across. The rim or top of the canyon is about 7,000 feet above sea level on the South Rim, and 9,000 feet on the other side, the North Rim. As a result, there are dif­ferent kinds of plants and animals on op­posite sides of the canyon. The South Rim is dry desert country. The North Rim has tall forests.

The canyon looks different at different times of day, and in different seasons and weather. At sunrise and sunset the red, gold, brown, and orange colours of the rocks are especially clear and bright. In winter, the canyon is partly covered with snow.

The view from the South Rim of the Grand Canyon is the best. Most visitors come to the South Rim and stay in camp­grounds or hotels. Every point along the canyon's edge offers a different view.

The North Rim of the Canyon is quieter. It takes all day to drive there from the South Rim because there is only one bridge across the Colorado River. On the way, you go through Navaho Indian lands, and a col­ourful pink desert called "The Painted Desert".

You can walk down into the Grand Canyon, or you can go down on the back of a mule. Inside the canyon, it is very hot — much hotter than at the top. You must be careful to carry enough water and not to get too tired. You can also take a boat trip down the Colorado River, and camp on the beaches at night. But whether you see the Grand Canyon from the top or the bottom, it will be an experience that you will never forget.

(canyon — каньон, ущелье; rim — край; mule — мул)

Exercises.

I. How much did you understand?

1. Are these statements true or false?

1. Today the Grand Canyon is one mile deep and 277 miles long.

2. The oldest rocks at the bottom of the canyon are only a million years old.

3. The South Rim has tall forests. The North Rim is dry desert country

4. In winter the canyon is covered with snow.

5. You can walk down into the Grand Canyon, or you can go down on the back of a horse.

2. Can you answer these questions?

1. What is one of the greatest natural wonders of the world?

2. What river formed the Grand Canyon?

3. Why are there different kinds of plants and animals on opposite sides of the canyon?

4. The canyon looks different at different times of day, and in different seasons, doesn't it?

5. Why do most visitors come to the South Rim?

6. How long does it take to get to the North Rim from the South Rim? Why?

g) What is ^“The Painted Desert”? h) Is it hot or cold inside the canyon? i) What is better, to see the Grand Canyon from the top or the bottom?

II. Speak on:

• the Grand Canyon, one of the greatest natural wonders of the world;

• the South Rim of the Саnyon;

• the North Rim of the Canyon.

III. Imagine you have visited the Grand Canyon. What would you like to tell your friends about the Canyon.

Ancient Forests: the Redwoods.

Redwood Creek is a small river in Northern California. Along this river there are five famous trees called “the Tall Trees Grove”. They are sequoia redwoods, and they are over 360 feet high. They are probably the tallest living trees on earth. The forest floor below is cool and dark. Damp fog from the nearby ocean sometimes hangs in the air.

Not far away, lumber companies are busy cutting down trees for wood. They cut down every tree in the forest at the same time. Even small bushes and plants are broken down by the trucks which move the huge trees. But the wood from one redwood tree can be sold for $15,000 or more, so cutting trees is big business. After a section of for­est is cut in this way, new baby trees are planted. But the new forest will probably never be the same as the very old forests, because redwoods need hundreds of years to grow.

Redwood trees are some of the oldest liv­ing things on this planet today. The oldest ones are from two thousand to four thou­sand years in age. The "General Sherman" tree in Sequoia National Park is probably 3,500 years old. It is 272 feet high and 37 feet across. Redwood trees once grew in many places. Just one hundred years ago, there were redwood forests for hundreds of miles along the Pacific Coast north of San Francisco. But 90 percent of the trees have been cut down in recent years. Now only a few redwood forests remain in California and Oregon, and even these are in danger.

Over the last twenty years, the U. S. gov­ernment has been buying forest land to add to Redwood National Park in northern California. And they want to stop the lum­ber companies cutting down nearby trees. But some local people are afraid that they will lose their jobs if all the forests become parkland. Some of the older redwood trees were young trees long ago, when the pyramids were built in Egypt. But every year the forest is cut down nearer and nearer to the Tall Trees Grove. Will these ancient forests still be here in the twenty-first century?

Exercises.

I. How much did you understand?

1. Are these statements true or false?

1. Redwood Creek is a large river in northern California.

2. The forest floor below is cool and dark.

3. Damp fog from the nearby ocean some­times hangs in the air.

4. Small bushes and plants are not bro­ken down when lumber companies cut down forests.

5. Cutting trees is big business.

6. The new forest will be the same as the very old forests.

7. The oldest redwood trees are from two thousand to four thousand years in age.

h) Redwood trees once grew in many plac­es.

i) Local people are glad that redwood forests will become parkland.

2. Can you answer these questions?

1. What is there along Redwood Creek? What is "the Tall Trees Grove"? What trees are they?

2. What are probably the tallest living things on the earth?

3. How do lumber companies cut down the forest?

4. What is the price of the wood from one redwood tree?

5. Are new baby trees planted after a sec­tion of forest has been cut down?

f) What are the oldest things on this planet today?

g) Where is the "General Sherman" tree? How old is it? What size is it?

h) Where do redwood forests remain? Are they safe?

i) What has the U.S. government been doing to save redwood forests over the last 20 years?

j) Why are local people afraid that red­wood forests will become parkland?

II. Speak on:

• "The Tall Trees Grove";

• lumber companies' business;

• the "General Sherman" tree;

• the U. S. government's attempts to stop cutting redwood forests.

III. Make up a project on whether these ancient forests still be here in the twenty- first century.