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THE SEA

Physical Environment
The planet earth has a great variety of physical environments. A physical environment is a place where organisms and creature live. It may be a field, a forest, a lake, a river, or a sea.

Living beings does not live in isolation from the world surrounds them. They form part of a whole ecosystem in which they interact with each other and with their physical environment.

Two hundred and fifty million years ago there are no snakes or frogs or even fish on our planet. Over a long period of time measured in a millions of years, ancient organisms underwent many changes, which produce the creatures that today inhabit the sea, land and air.

The Changes in the Sea
Life in the sea today is different from what it must have been when it first began there.

The sea has always been a source of food and energy for human beings, as well as a means of traveling from one place to another. But in modern times the sea has also been used as the world greatest rubbish dump. In spite of this, life has managed to continue, thanks to the sea’s natural ability to purify itself.


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THE SEA'S CHARACTERISTICS

Salinity
The important components of the sea water are salt, gases, and other dissolved substances. Seawater also contains particle of calcium, iron, copper, silver, and even gold.

However, the most abundant element is sodium chloride, or common household salt. The sea’s salinity, or salt content differs from place to place. In Polar Regions, the sea’s salt content is low; on the other hand, salinity is very high in the tropical areas. Salinity is related to the water’s density. Salty water is denser than the water with less salt.

Sea Current
Some sea currents are produce by winds that blow on the sea. But most important sea currents are produced by difference between the salinity temperature, and density of water. Sea current moves the water around, enriching the oceans with oxygen and carbon-dioxide.

The oxygen is breathed by the fish and other marine life, while carbon-dioxide is used in food production and photosynthesis carried out the sea plants.


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Waves caused by winds



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Unlike waves, sea currents create horizontal movements in the water. Some of the main sea currents transport warm waters from the euqator to the poles, making ht oceans a moderating elements of the world's climate.
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The Sea’s Inhabitants
The deepest parts of the sea are darker and colder.

Some of the creature that live in the depths are blinds. They do not need sight because light never reaches the sea’s bottom. These creatures feed on other animals, since plant life cannot exist without light.

The sea’s surface is home to some very small organisms that content chlorophyll, just like other green plants. They are known as phytoplankton. Living off phytoplankton are the tiny organisms known as the zooplankton.

All sea creatures ultimately depend on the phytoplankton for food. The life of these little plants depends on the amount of sunlight and the presence of certain mineral elements in the sea. Although the sunlight only penetrate the upper parts of the sea and does not go down further than about three hundred feet, minerals are found at the ocean bottom.

Vertical Currents
Nature has developed its own mechanism for bringing up the minerals to the surface of the sea plants to live on. Through vertical movements in the water the minerals ascend from the bottom to the upper parts of the surface. These vertical currents make it possible for plankton to thrive.


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From the ocean depth to the surface

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THE WATER CYCLE

The Seas
It is important to find the beginning and end of a sea, because, in reality, all the seas on our planet are one. The waters from one sea are connected to the others.

Waters covers three quarters of the earth’s surface. People have divided the sea into different oceans and given them names: the Pacific, the Atlantic, the Indian, the Artic, and the Antarctic Ocean. Seas and oceans are unique to our planet in the solar system.

About 2.5 billion years ago life began in the sea. Since then, life on the earth sustained by the existence of the sea.


The Water Cycle
Climate, the shape of the mountains, and the way our planets different creatures live all depend on the sea.

The clouds, the rain, the snow, and the rivers and lakes are created by the action of seawater. The sun heats seawater, which then evaporates. The water vapor then condensed to become clouds, from which rain or snow falls. The water then returns to the sea by the way of rivers and streams. Some of the water filters through the ground and forms underground reservoirs. All of this is what known as the water cycle.

Day after day, year after year, for millions of years, the sun has evaporated seawater and then returned it to the sea along rivers. Water itself has never stopped renewing itself.

The quantity of earth’s water has remained constant because water is not destroyed when it is used. Water comes to us in the form of clouds, rain, snow, rivers, lakes, and seas.




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The Water Cycle

THE WATER IS SCARCE

The Development of the Cities
Since ancient times, people have banded together in communities. The smaller communities live mainly on agriculture and live stock raising. The bigger ones depended on industry and commerce.

Water has been an absolute necessity since the first urban communities were formed. Historically, when a city reached a maximum number of inhabitants, some of those inhabitants would build a new city in an undeveloped area. Uncontrolled urban growth meant serious water supply problems.


Water Consumption
The enormous cities of Calcutta, Sao Paulo, Hong Kong, and Mexico City have grown more than anyone could have expected. What has happened to their water supply?

Lately, consumption of water worldwide has quadrupled, going from 200 cubic mile to 800 cubic miles. This is not only because of an increasing population but also because today’s agricultural systems and industrial process need more water.

Every day, in every house, people turn their taps and out flows water from nearby reservoir. It is the water we consume when we drink, wash, cook, and water the plants.

Canals have been built and rivers diverted; water from the underground aquifers has been extracted. But the government of the countries where is scarce have to impose restrictions on its use and promote campaigns to cut down individual water consumption.


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Water is scarce

LIFE IN THE SEA

A Thousand Forms of Life
The variety of plant and animals that we see in the sea represent just fraction of the great diversity of life that exist there. Even though the sea is not the richest biological environment, it does contain immense assortment of plant and animal life.

Along with the best known marine animals, there are thousand of other organisms live under the sand of the sea, in the seaweed, inside the hole of rocks, or within the bodies of sea creatures.


The Food Chain
Marine animals, like other living beings must search for food they need to survive in their environment. If we look closely at how one particular sea organism look for food we will discover the beginnings of a sequence known as food chain. Each and every organism animal and plant, forms a link in the chain. In the sea there are thousands of such food chains made up by various species.


The Links in the Chain
In every food chain, we see that the animals have to search for food, since there is no animal that can produce it for itself. We also see that each chain always begin with a green plant.

In chain the producer organism is the plant. The animals making up the rest of the links are called the consumer organisms.

The sea’s main producer organism is phytoplankton. The primary consumers are zooplankton. The secondary are tertiary consumers are invertebrate marine creatures and fish of different sizes, are birds and mammals.

Sardines and anchovies feed on zooplankton. Tuna eat sardines, anchovies, and other species of fish, just like the shark, which also eats tuna. Anchovies, sardines, sharks, and many other fish form part of different chains. For this reason, when fish search for food, they established a wide variety of relationships, creating a real food network.

The remains of creatures sink to the bottom of the sea floor where they are transformed by the bacteria into new matter that will in turn be used as food by phytoplankton. And then the process will start again.


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Life in the sea

IN SEARCH OF FOOD

Life in the Sea
The life of an animal or plant depends, to certain extent, on the conditions of the place or ecosystem in which it lives. If we take the sea's ecosystem as an example we can see that the organisms that live in it have taken maximum advantage of their ecosystem.

One of the special characteristic of the sea's inhabitants is their increased capacity of reproduction. The millions and millions of sardines, mackerel, cod, and other fishes that live in the sea are capable of producing hundreds of thousands eggs every year.

But even the smallest plankton organisms can reproduce in the same numbers. In winter and in spring, when the deep waters of the sea rise to the surface carrying large quantity of nutrients, they reproduce at such a speed that in a short time the water takes on a greenish and sometimes reddish color as result of large number of microorganisms that have been produced.


Species Distribution
At certain time of the year and in some areas the distribution of animals and vegetation is unequal. The fish that inhabit the water surface, such as sardines and mackerel, are normally found in the most productive areas, that is to say, where there is abundant plankton for the fish to live on.

Bigger, fish such as tuna, travel long distances; their food sources is not limited to one particular area.


Survival in the Sea
Which species has the greatest chance of surviving when food is in short supply? It is the species with widest range of food to choose from.

The sea is not a biological diverse environment. Of the several million species inhabiting our planet, only 150,000 species live in the sea. For this reason, the sea's food chain is fragile and alternation of just one of its links could be disastrous to many creatures.


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In search of food

THE SEA’S RESOURCES

Oil
People have always exploited the sea’s resources.

Deep under the sea’s floor lie deposits of oil, industrial civilization’s main source of energy. From oil we obtain gasoline for cars and fuel for ships, airplanes, factories and electrical generating station. There are also secondary products made from oil, such as insecticides, detergents, and a great variety of plastics.

A fourth of the world’s oil is being extracted from the bottom of the sea. New, more sophisticated techniques of oil extraction mean that we can drill deeper to find new deposits.

When oil started to become important in the developed world, construction began on bigger sea ports to help transport it. Shipbuilding adapted itself to this industry by constructing special oil tankers.


Fishing
Fishing is no longer a small scale activity. It has been rapidly converted into an enormous industry that exploits the sea’s resources for economic profit.

But marine creatures cannot reproduce themselves as fast as they are being harvested, and fish stocks are being depleted.


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The Sea's Resources

A BLACK SLICK

Energy
In order to transform materials into the many producers that people in the developed world have come to depend upon, industry requires energy. Almost ever product and devices in our homes and lives, from automobiles to furniture to fabrics, is shaped and constructed through the expenditure of energy, and most often the source of that energy is oil.


Transporting Oil
Oil has to be transported from pumping sites to industrial areas, however far apart they may be. The third of the earth’s oil travels the sea lanes of the world by ship. When an accident occurs, oil spills into the sea, causing an oil slick, which can spread out over a wide area.


Ecological Consequences
The oil slick prevents the light from penetrating the sea, which in turns prevents the plankton from developing and damages the food chain. Furthermore, oil is toxic and kills sea life.

The tar from the oil can slowly sink to the bottom of the sea, preventing the marine current from transporting mineral substances from the depths to the sea surface. Finally, we must not forget about the damage to beaches and coastal areas, as well as the threat to fish and birds.


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A Black Slick

SEA POLLUTANTS

Improving Crops
With the aim of getting maximum yield from crops and combating the diseases that can ruin them, farmers apply to their fields’ chemical products known as fertilizers and pesticides.

One hundred years ago, one of the best known pesticides, DDT, began to be used. It was absorbed through the skin of insects, causing their almost instant death.

But DDT also affected other animals. It caused birds to lay eggs whose shells are so thin that they broke before chicks hatched. DDT had the same effect on the shells of mollusks in the sea.


By Way of Rivers
Rainwater washes the fertilizers and insecticides used by the farmers down to rivers. The river carries them down stream to the sea.

Fertilizers and pesticides do not degrade easily. They remain in the water, where they can be swallowed by marine life.

These substances then begin to circulate the food chain and their effects are apparent in its different links, from plankton to fish. Through contaminated fish, it finally reaches human beings.

Intensive use of crop fertilizers in order to combat famine-in a world with a population bordering on six billion people- and use of insecticides to control pests can create serious problems.


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Sea Pollutants

SEWAGE

Sea water is polluted when it contains substances that cause the loss of its natural characteristics. For example:

• When the oxygen that marine creatures need to breath is lacking.
• When ocean water contains insecticides or radioactive fallout.
• When oil or tar prevent plankton from developing nutrients that other organisms on the food chain need.
• When the nutrient renewal process of upwelling currents are off.

In summary, water is polluted when the relationship between the plankton and light, plankton and other marine organism, and the sea bed and the surface are damaged.


The Causes of Pollution
Many pollutants reach the sea as a consequence of human activity. Rivers carry the fertilizers and insecticides used in agriculture into the sea. They also transport toxic waste from the factories placed on their banks. Villagesand towns throw their sewages into the seas and river.


Purifying the Water
Both industrial waste and sewages are pollutants. This is why it is necessary to cleanse water before it re-enters the water cycle through rivers, seas, and clouds.

The process of cleansing depends on the level and the type of pollutant. Some of these processes are very complaex and expensive. Water must go through the following processes to be purified:

• Solid waste and larger particles must be filtered out and separated.
• Smaller particles are allowed to settle at the bottom of tanks or cisterns as slime or mud.
• Other particles suspended in the water are removed through further filtration and coagulation. That is by bonding the pollutants to heavier particles that settle out as sediment.
• The purified water is drained through submerged pipes that carry it a certain distance from the shore in order to disperse it in to the sea water.
  
  

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Sewage