In which part of the ocean is the largest number of organisms concentrated?

In the surface layers of water, to a depth of not even 200, but about 100 meters, the bulk of the living creatures of the oceans are concentrated.
This is where the maximum:
illumination;
temperature;
the concentration of dissolved oxygen.
Due to such favorable conditions for development and reproduction, the diversity of species is enormous. Widely represented small organisms serve as large food, therefore, food is most of all here. Plankton and the vast majority of underwater plants feel comfortable only near the surface and are not found in other layers.
The middle layer, up to a kilometer (where the light is much less, colder, less oxygen and higher the pressure of the water column) and the lower layer, which extends to the very bottom (where the light does not penetrate at all, the temperature is close to zero and the pressure is extremely high), are also distinguished.