Short essay on the Distribution of Marine Life

In the ocean there are four great zones which have different conditions giving different characteristics to the marine organism. These zones are: (1) the littoral zone representing the coast and shallow water near the sea coast, (2) the pelagic zone, or the upper layers of the ocean water, and (3) the abysmal zone, or the deep seas, and (4) the zone of intermediate depths.

Life in the littoral zone:

The coast line is characterized by conditions intermediate between those of land and sea, so there is similarity between the lives in the two. The polar bear, for example, is classed as a land animal, but it also spends much of its time on the ice floating in the sea.

On the contrary, seal and walrus, though classed as marine animals, stay out of water a large part of the time. So is the case of some of the birds which pass their time both on the sea and the adjoining land. However, the majority of marine organism is largely confined to the coast region and shallow waters bordering it.

In the littoral zone the marine organism differs in form, habit, and abundance depending on physical conditions even within short distances. Besides local differences due to variation in environment, there are differences due to climatic conditions.

In the shallow coastal waters life is abundant and varied. In the cold waters of the Arctic region there are many large animals which feed upon this life such as – diving birds, seals, walrus, cod and halibut. Edible fish is largely confined to the outer margin of the Arctic zone.

In the tropical regions the littoral fauna is varied and abundant. Here the brilliant sunshine and warmth encourage plant growth. The shallow coastal waters are densely occupied by organisms such as reef building corals.

Here the bottom of the sea is inhabited by such fixed organism as burrowing, crawling, swimming and floating species. The marine organisms in this Torrid Zone are beautiful in form and colour.

Life in the Pelagic Zone:

There is the great abundance of minute organisms in the surface layers of the ocean. These organisms comprise both plants and animals. Mostly they are classed as floating forms. These species are widely distributed, since they are carried away by the waves and currents.

In addition to minute organisms, there are numerous kinds of larger floating and swimming species. Among the larger animals there are many fishes which swim in great schools like herring and mackerel, while others move singly like the shark and swordfish.

The whale is also found in the surface and upper layers of the ocean. The pelagic animal life thrives on the abundant plant life, specially the microscopic algae. The pelagic animal life is widely distributed. These animals are mainly floating and free-swimming.

Life in the intermediate Depths

Formerly it was believed that there was complete absence of life in the intermediate zone. But later on it was discovered that this zone is also inhabited by marine life.

However, little is known about the distribution and variation of these animals of the intermediate zone. Because of uniformity of conditions in this layer, the marine fauna is widely distributed. Variation in the marine life is more rapid vertically than horizontally.

Life on the Ocean Bottom (Abysmal Zone):

The fish which live near the bottom of the sea are called demersal fish. There is abundant marine life on the bottom of the oceans. Here the marine organisms vary with the temperature and the supply of oxygen and food. Where the warm ocean currents flow at the bottom, they bring with them warmth, oxygen and food.

The marine life in this zone is varied and abundant. However, where there are barriers to check free circulation of water, there is so little oxygen that the existence of life is impossible. No life except bacteria exists there. This is the case in the Black Sea.

In this zone of darkness, there is a complete absence of plant life. Life on the ocean bottom is limited by the scarcity of food supply. However, the ocean bottom ooze supplies food to burrowing animals.

Besides, one form of life on the ocean bottom preys upon another. Some of the ocean bottom animals depend upon the supply of food that falls down from the upper layers which are densely inhabited by marine organisms.

In addition to food, the marine animals provide numerous other valuable commercial products such as, whale and seal oil, whalebone, sealskins, walrus teeth, corals, sponges, pearls and tortoise shells.

To quote Richard P. Mckenna, “Satellites can greatly improve the efficiency of fishing operations by directing boats to the most promising areas.

Sensors may detect oil slicks and surface vapors produced by schooling fish, or may determine the most likely locations of schools on the basis of the physical state of the ocean, the temperatures of interfacing currents, and the abundance and distribution of nutrients. Fishermen obtain the data either directly from the satellite or indirectly via a ground station”.