Life in the Upper Layers

The Ocean provides a favourable environment for life and the development of plant and animal organisms. All organisms living in the Ocean are divided into three large groups:
  • The vegetation (plants) such as seaweed and photosynthesising bacteria, using solar energy, transform biogenic nutrients using a process of photosynthesis. Also in this group are many bacteria that convert mineral substances to organic substances by a process called chemosynthesis.
  • The second group, animals, consume plants and other animals.
  • The third group feeds on the remains of plants and other animals and also serve as food for many organisms.
In the Ocean, therefore, a dependency exists between its living things. Food is the primary dependency, followed by the effects of life on Ocean productivity and then our ability to use sea life as a resource. The diverse vegetative and animal life in the Ocean is extremely non-uniform in its distribution. Next to areas with abundant sea life, such as zones of upwelling, there may exist areas that have almost no living matter. These are similar to deserts on land. On the globe there exist 63 classes of animals and 33 classes of plants, a basic part of which live in the oceans (76% of the animals and about 50% of the plants).

Life at Depth

The World Ocean as an environment for vegetable and animal organisms is subdivided as such: pelagic (living in the layers of water from the surface to the bottom) and benthic (living on the bottom of ocean) In the pelagic class, epipelagic, mesopelagic, bathypelagic and abyssopelagic life forms live. Below the 3,000 depth and extending to the deepest parts of the ocean is the abyssopelagic zone. Inhabitants of the abyssopelagic zone are often colourless. The fishes and crabs most often have no eyes but some have special flashing organs used to assist them to find food. For distribution of benthic organisms (living on the Ocean bottom) a number of zones have been allocated. The upper zone - littoral and sub-littoral includes places from the tide line to depths of about 200 m; bathyal includes the range from 200 to 3,000 m; abyssal takes in the zone from 3,000 m and ultra-abyssal takes in the zone from 6,000 m to the floors of the deepest trenches in the Ocean. The littoral and sub-littoral are characterised by the greatest species varieties and abundance of food. Only in this zone does bottom vegetation develop..

Areas where Organisms Live in the Ocean

I. Pelagic 1. Epipelagic 2. Mesopelagic 3. Bathypelagic 4. Abyssopelagic II. Benthic 5. Littoral, Sub-littoral 6. Bathyal 7. Abyssal 8. Ultra-abyssal

Text and images are from Man and the Ocean, a CD-ROM produced by the Russian Head Department of Navigation and Oceanography (HDNO).

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