Of the planets of the solar system, the earth we live in alone has water in plenty. Nearly 97 per cent of all waters are in the seas. These seas and oceans are a reservoir of heat. Therefore, the seas are generally hot in summer and cold in winter. Of the solar heat reaching the earth, a fourth is used in evaporating the sea.
The sea surface temperatures vary from place to place. In the equatorial regions, it is high and it is progressively low as we go from the equator to the poles. In the sea water, there is a high concentration of mineral salts and salinity. Salinity also differs from place to place. The ratio of salinity depends upon the addition of freshwater in the seas and the rate of evaporation. Waves, tides and currents are the movements of the ocean waters. They influence the temperature, moisture and rainfall of the coastal areas they flow to. Cold currents bring with them the planktons from the poles and the sub-polar regions. The mixing of warm and cold currents helps with the proliferation of ocean /sea organisms along the continental shelves. You are already aware that the living organisms appeared first in the seas. The vegetation and animals of the seas are quite different from the flora and fauna of the land. They live in the continental margins, islands and in the deep seas.
Among the sea ecosystems, there are four major and very important ecosystems useful for humankind. They are: the wetlands, the marshes, the estuaries and the coral reefs.
Temperate tidal lands become wetlands and the tropical tidal lands become marshes. In these lands, the sea grasses and the flowering plants are abundantly seen. These plants are consumed as food by the shell fish and the shrimps. They are the food stored for the temperate geese and flamingos. Further, they are a filter for the wastes from land and prevent sea erosion along the coast. As the fresh and brackish waters meet at the estuaries, these waters
are conducive environments for crabs, oysters, prawns and shell fish. Thus the estuaries are a suitable environment for sea organisms.
Of the sea ecosystems, one is of the coral reefs. There are several different organisms living with them. These are also the ancient of the ecosystems. Corals have existed from the very beginning of the sea life.
Before growing as colonies, they generate chemical products and expand their areas of colonisation. With the metamorphosis of the chemi-cal products, other organisms are unable to colonise these areas. To provide resistance to the disease causing germs, the humans use them as raw materials for medicines.
Corals. Corals live in colonies and they are a collective. They are micro organisms living in shells known as 'polyps'. The polyps are made of calcium, extracted from the sea by the corals. The corals are stuck together and live as one massive organism even though they are such tiny creatures. The substance that fastens them is produced by the corals themselves.
Corals live only in the tropical seas. They cannot survive in waters with temperatures below 20o C. Hence, they are not found in areas of high latitude temperate regions. They are normally found between 30o N and 30o S. The food and the warmth they require are obtained from the ocean currents. Like the plants, they require sunshine as well. So they are found beneath the sea waters but only until where the sun's rays penetrate and where the temperature is warm enough for their comforts. Waves however hamper their growth. It is for this reason, they are found growing along the coast, hanging on to the land. The wave-cut platforms provide for a place for the corals to attach to.
Corals are of three types. They are: Fringing reef, Barrier reef and Atoll.
In the southern seas of India, we have fringing reefs. Lakshadweep islands are entirely made of corals. In the Caribbean also, there are coral islands. Right along the east coast of Australia, there is great barrier reef stretching for thousands of kilometres. They are now tourist and recreation spots. Tourists flock these places in large numbers to see the colourful variety of sea animals around the reefs. There are therefore diving facilities in these regions.
Atolls are the complex coral features, raised around the islands by coral colonies over thousands of years. In between, there is a shallow lagoon. In these atolls, the corals get exposed as the water in the lagoon goes down. Atolls, it is said, have a fascinating origin.
Apart from these sea organisms, there are several others: plankton, necton and benthos.
The floating, micro organisms are normally known as the planktons. With the movements of the seas, the planktons migrate along with the currents and oceans. Diatom is a plankton with a single cell. Nectons are swimming organisms. Fish, whales, and seals are nectons. A majority of the sea animals migrate for food and breeding. The mammalian seals are a restless animal, moving hither and thither. Some of the whales migrate from cold waters into warm waters.
Algae are sea mosses seen on surface of the sea waters. On the contrary, those that are found beneath the sea surface are benthos. In these, there are moving and non-moving creatures. For example, large sea crabs, shells, star fish and worms are the moving creatures. Sea plants, sea weeds, mosses, corals, oysters and sea foams are non-moving varieties. Benthos live in areas where the sun penetrates deep into the waters. They are also found in deep oceans in certain areas.
The sea organisms described above are in some way useful to the humans. Consumer commodities such as cosmetics, shampoo, dyes and lubricants are all manufactured using sea organic raw materials. At the same time, the oceans and seas are being polluted by the human activities. The wastes from the cities, industries, atomic reactors and oil refineries are being dumped into the sea along the coast, causing concern for pollution. The pollutants from these affect the sea organisms and also destroy them. If we do not control the pollution of the oceans now, the living seas may one day become the dead seas.
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