Question

the dark zone of sea is called as

Answer 1

90% of the ocean lies in the bathypelagic (aphotic) zone into which no light penetrates. This is also called the midnight zone and the deep ocean. Due to the complete lack of sunlight, photosynthesis cannot occur and the only light source is bioluminescence.

Answer 2

The dark zone of sea is called as the bathyal zone. The bathyal zone of the ocean extends from a depth of one thousand to four thousand metres (3,300 to 13,100 ft) below the ocean surface from the sea level. The average temperature hovers at about 4 °C in the bathyal zone. The bathyal zone is densely populated by various flora and fauna which are found in the deep of the ocean. Sunlight doesn't reaches this zone.