The co-relation between water and light and how the last affects the first causes a variation in the kind of sea life which a diver might be able to enjoy while practicing the sport. Water and light affect each other as well as affect the way in which humans can interact with the sea depending on them.
This co-relation between water and light affects divers not only by causing variations in their vision but also by allowing them to see completely different kinds of sea life. The sea life which a diver might be able to see at day time is completely different than the one he could enjoy during night. Besides this, sea life also varies depending on the water depth in which a diver is and the amount of light that such depth receives.
There are three main sea regions in which different amounts of light reach and in which different kinds of fauna and flora can be found. These three sea regions are: the sunlight zone, the twilight zone, and the midnight zone. Each one of the three main zones have its own characteristics and is a whole different sea world that the others. Besides these zones, the coast line is also often seen as another sea region due to the way it can also show a specific sea activity.
The sunlight zone is the water region that is closer to the surface and therefore it is the one which receives the highest amount of light. The co-relation of water and light of this zone allows more than 90% of sea species to live in it. Besides, the sunlight zone is the only one in which plants can live due to the amount of light they receive in it.
The second sea region is the twilight zone. In this zone we can find sea animals such as shrimps and squids. And the third sea region, called the midnight zone, is the deep dark sea area where light doesn`t reach. In this zone only about 1% of sea species live, and animals such as sharks have their habitats in it. The temperature in the midnight zone is almost freezing and water pressure is very high.
Source: Dive Pilot