EARTH : marine world " ocean "

 The ocean :

    The ocean is a vast environment. A large number of animals and plants live on its soil, but many others, able to float effortlessly at the depth that suits them, spend their lives drifting or swimming in the open sea, near the surface and in the sea. twilight zone of the ocean. Most live at a given depth, but some change depth between day and night. In contrast, only a few rare insects live entirely in ocean air. 

 >> Staying permanently in the light ocean air requires a lot of energy.

The vertical division of the marine environment :

1. Sunlit or epipelagic area (including surface) : 0-200 m 

 > Marine life : plankton, jellyfish (flying fish), fish that live in schools like herring, fast predators like tuna, also there are swordfish, sharks, and dolphins. 

 2. Twilight or mesopelagic zone: 200-2000m

> Marine life: animal plankton, small silver fish with big eyes such as lantern fish, squid, shrimp. 

 3. Abyssal zone (bathypelagic zone and abyssopelagic zone which includes oceanic trenches): 2,000-10,000m

> Marine life: small fish with large stomachs such as sea buckthorn, anglerfish, pomegranate.

The marine environment :

    Life in the water is very different from life on land. Water, much denser than air, physically supports what is in it. The blue whale, the largest known animal, can measure 30m in length. No animal of this size could live on dry land. It would simply be too heavy to move around. Also, noise travels much faster in water than in air, which helps marine animals communicate with each other. Whales can thus call to each other across very great distances.

Overwhelming pressure !

    Atmospheric pressure is generally measured in bars. One bar is equivalent to about 1kg of pressure per square centimeter. When you sink into the ocean, the water pressure increases by one bar every 10m. Sperm whales descend without difficulty to a depth of 1000m (or even 3000m), a level at which the pressure <10 times higher than at the surface> compresses their rib cage and their lungs. No human would survive such pressure. Whales do this by using the oxygen present in their tissues when they are underwater and by re-inflating their lungs when they resurface. Animals deprived of air-containing organs, such as deep-sea fish, are insensitive to increased pressure.

Echinoderms :

    Scientists think that life on earth was born in the oceans before spreading on the ground. Most large groups of animals (phylums) have marine, terrestrial and freshwater representatives such as snakes or snails. There is, however, a large group of animals, called echinoderms ((with thorny skin)), which is found only in the oceans like: sea stars, sea urchins, and sea cucumbers.

When red turns white !

    Sunlight is made up of all the colors of the rainbow (red, orange, yellow, green, blue, indigo, and purple). In the ocean, red objects like this lionfish (top right) - or a diver's blood! - appear dull bluish, because red light waves do not penetrate deep into the ocean. The artificial light of a flash or a diving lamp makes it possible to observe the real colors of the animal (bottom right).

Reduced visibility :

    On a clear day, on dry land, it is possible to see mountains and hills located miles away. While even in the clearest tropical sea, a diver can only see what is within a radius of about 50cm. Plankton and silt floating in the water greatly reduce visibility near the coast.