There are variety of plants and animals in the ocean. Generally, the lives in the ocean are controlled by the intensity of light, depth of ocean water, ocean currents, availability of nutrients and amount of dissolved chemicals and gases.
The marine environment can be divided into a number of zones or realms:
(1) Along the surface water from the coast to mid-sea;
(2) Along the floor of the ocean; and
(3) In depth from surface to deep ocean floor.
The marine environment is divided into two major zones. They are called pelagic and benthic. The pelagic actually refers to the open ocean and includes all the water mass. The benthic zone refers to that part along the ocean floor where organisms are available.
The pelagic zone is again subdivided into two more subdivisions. They are called neritic and oceanic. The neritic zone is a shallow zone and has average depth of 200 metres. This zone is most significant to marine life and almost all the marine fishes live in this zone.
The oceanic zone has depth of more than 200 metres. It is divided again into two subzones— upper lighted zone and lower dark zone. The oceanic zone has relatively uniform temperature and salinity. The water of this zone is clear.
The benthic realm is divided into two zones littoral and deep sea. The littoral zone extends up to a depth of 200 metres and is full of primary food for animals. Fishes live in this zone. The deep sea zone extends from 200 metres to the deepest trench in the ocean floor (Fig. 5.13). It is characterised by low temperature and permanent darkness. The marine lives decrease with the increase of distance from the coast. Most of the organisms of this zone are carnivorous.
According to the style of movement and mode of living, plants and animals of the ocean can be divided into three major groups:
Planktons live under varying conditions of temperature, salinity, ocean currents and light. There are both plant and animal planktons. Plant planktons are known as phytoplankton and animal planktons are known as zooplankton.
The planktons have following characteristics:
1. They are floaters without self-propulsion.
2. They are microscopic in size but with a few exceptions like jelly-fish, brown algae and sargassum.
3. Planktons live in shallow water, flourish rapidly in cold water and are brought by cold currents to temperate region.
4. They absorb sunlight and nutrients.
Benthos are organisms that live in ocean floor. They are both mobile and immobile. Most benthos are found in shallow water but with a few exceptions. The mobile benthos include lobsters, crabs, snails and worms. The immobile benthos include-seaweeds, corals, sponges, oysters, etc.
Nektons are an advanced form of animal in relation to planktons and benthos. They are the swimming organisms and live below the surface water where food is plentiful. Nektons include fishes, dolphins, whales, etc. They primarily live on zooplanktons and move from one place to another in search of food and breathing. Dolphins are among the most intelligent animals in the world.
The marine vegetations are of limited variety and they are commonly known as algae. Algae consist of primitive plant forms and may grow on plants and animals. The algae that grow on other plants are called epiphytic and those that grow on animals are known as epizoic. The most common algae are blue-green, green, red and brown.
The ocean floor is mostly covered with the sediments brought by running water, wind and sea-waves. This layer of sediment can be compared to the soil cover over the continents. The ocean deposits differ greatly from one place to another. The study of ocean deposits is very important for the understanding of the most of the rock structure and composition of the folded mountains of the world.
On the basis of the place of occurrence, ocean deposits can broadly be divided into two major classes:
(i) The deposits of continental shelf and slope, and
(ii) The deposits of deep ocean floor and trenches.
The deposits of continental shelf and slopes consist mainly of materials brought from the land. They are called terrigenous deposits. The deposits of deep ocean floor are made of the skeletons and shells of marine animals and plants. They are called pelagic deposits. However, it should be remembered that the above two types of ocean deposits are not distinctly separated from each other and rather they occur as mixtures.
The terrigenous deposits consist mainly of terrigenous materials, organic deposits and volcanic deposits. However, major portion is composed of rock materials. The larger fragments of rock are deposited near the shore and the finer materials are carried far into the deep sea. The distance to which the materials are carried away largely depends on the size of the materials, slope of the ocean floor and on the strength of waves and ocean currents.
Therefore, from the shore outward there is a gradual decrease in the coarseness of the deposits. On the basis of the size of the rock fragments, the sediments can be classified into gravel, sand and mud. Generally, major portion of the continental shelf and entire continental slope are covered with mud.
In course of time, these deposits transform into sedimentary rocks. Quartz is the most abundant rock forming mineral. Soil Scientist Murray classified mud into three main classes based on colour of the sediment as-red mud, blue mud and green mud.
Continental shelf is the living place of many animals and plants. In course of time, the skeletons of animals and decayed parts of the plants form the greater part of the deposits. They are changed into sand and mud through mechanical and chemical processes. These deposits mainly contain calcium carbonate. They are completely different from the terrigenous deposits and are generally called organic deposits.
In the volcanic zones of the continental shelf and slope, the deposits are made up of the lava that comes out of the volcanoes. These deposits differ from the other two types as they contain fragments of lava instead of either quartz or organic matter. This type of deposit is called volcanic deposit.
Nearly three-fourths of the ocean floor is covered with the pelagic deposits. In pelagic deposits, terrigenous materials are completely absent except a small quantity of volcanic materials in certain places. The pelagic deposits are both organic and inorganic in nature. They consist mainly of organic matter derived from skeletons of ocean animals and plants and from volcanic dust brought by wind.
The organic deposits are found as liquid mud generally known as oozes.
On the basis of the availability of predominant type of organisms, oozes are classified into two classes:
(а) Calcarious ooze, and
(b) Siliceous ooze.
Calcium carbonate is predominant in calcarious ooze and silica is abundant in siliceous ooze. The calcarious ooze is again subdivided into two classes on the basis of the kind of organism present.
1. Pteropod ooze:
This type of ooze is composed of tiny calcarious shells of pteropod (a kind of mollusc). It is widely spread on the ocean floors but mostly confined to the Atlantic ocean.
2. Globigerina ooze:
This type of ooze is formed of the calcarious remains of minute protozoa called globigerina. It is widespread in the Atlantic and the Indian oceans.
The siliceous ooze also can be subdivided into two classes.
1. Diatom ooze.
2. Radiolarian ooze.
The diatom ooze is formed of the cells of tiny diatom plants. It is found mainly in the south sea and outside the limit of the terrigenous deposits. It is also found in a narrow belt in the Pacific ocean.
The radiolarian ooze is made up of the organic remains of the planktonic organisms. Silica is predominant and it is found in the deep equatorial part of the Pacific Ocean.
In addition to the different types of oozes, there is another deposit found in the ocean floor. It is known as Red clay. It consists mainly of the inorganic materials of volcanic origin. Red clay is mainly made of silicon and aluminium dioxide. However, it also contains manganese, phosphorus and radium. Red clay covers nearly 38 per cent of the ocean floor and more than 50 per cent of the Pacific ocean.
The oceans are great store house of food and other marine products of value to man. Fish forms a valuable source of food and nutrition. Fishes contributes more than 12 per cent of the animal protein food that man consumes. In addition to fish, man also eats molluscs, and many other edible forms of meat and certain kind of sea weeds. Many sea animals provide oil, leather, glue, cattle feed and other useful products. Certain sea animals and plants are also used for making medicines.
A large number of metallic and non-metallic minerals are found in the ocean floor. Minerals occur both in solution and suspension. The sea water contains magnesium and bromine in addition to common salt. The other important minerals include—manganese, phosphate, sulphur, gold, platinum, iron, tin, diamond and many others.
The most important minerals produced from sea floor are Petroleum and Natural Gas. These two minerals account for more than 90 per cent of all minerals available in the ocean. Petroleum is found in the continental shelf and slope.
It has been estimated that about 20 per cent of the world’s total reserves are deposited in the ocean floor. In India, Bombay high is an important oil producing region. It is also estimated that by the turn of this century nearly 40 per cent of the world’s oil production will come from oceans.
The third important resource of ocean is the energy resource. The energy resource is derived from tides, geothermal sources and temperature differences. The powerful tidal waves release large amounts of energy when they strike against the sea shore. However, there are certain difficulties in tapping the tidal energy. A few tidal power stations are working successfully in the USSR, France and Japan.
The geothermal energy is associated with the areas of active volcanoes and fracture zones. Geothermal energy has already been developed in the USA, New Zealand and Mexico.
The temperature differences of the sea water also help in generating energy. The surface water of the tropical region may have 25°C to 30°C of temperature while the deep water below may have less than 5°C. This gradient of temperature is quite sufficient to run a generator and to produce electricity. Floating generators based on temperature differences have been designed in Belgium and Cuba.