The sun is not a source of energy for the organisms living in
The availability of light on land is closely linked with that of temperature since the sun is the source for both. But, deep (>500m) in the oceans, the environment is dark and its inhabitants are not aware of the existence of a celestial source of energy called the Sun. The autotrophs living in deep sea are chemotrophs. Particle organic matter and dead bodies sinking from the photic zone provide source of energy to the decomposers and animals in the deep sea.