In the twilight zone, the temperature and the light conditions change. The initial 200 meters of the ocean as considered as the open ocean. There is availability of light and thriving temperature there. Butt below that, in the 'deep ocean'. The availability of light decreases and as we go further down, the light no longer reaches those parts of the ocean. Moreover, the temperatures plummet down to almost freezing conditions. In addition to this, the pressure is much more higher in the deep ocean.
