Here's why:
* Photosynthesis: Autotrophs, like phytoplankton, need sunlight to perform photosynthesis. Photosynthesis is the process by which they convert light energy into chemical energy (sugars) for growth.
* Light Attenuation: Sunlight rapidly weakens as it penetrates the water column. This is due to absorption and scattering by water molecules, suspended particles, and organisms.
* Aphotic Zone: At depths below around 200 meters (650 feet), the amount of light is insufficient for most photosynthetic organisms to thrive. This region is called the aphotic zone.
While other factors like nutrient availability and temperature can also play a role, the lack of sunlight is the primary limiting factor for autotroph abundance in the deep ocean.
