6ebbba77_Marine_habitats__principles__Living_in_the_sea
[Factor] Temperature [Living on the land] Fluctuates enormously from night to day, winter to summer and from sea level to mountain top. It is relatively easy to protect against the cooling or heating effect of air as air is 800 times less dense than water. Animals can be warm-blooded, which allows them to live in hostile places. [Living in the sea] 
Fluctuates little from night to day and winter to summer. The water is 800 times denser than air and its cooling effect is tremendous. Creatures cannot spend the energy to stay warmer than their surroundings and are mainly cold-blooded. Warm-blooded whales and dolphins live in the sea but they don't breathe water! Cold blooded animals spend very little energy when sitting still. They go on 'stand-by'.
Marine habitats, principles
Living in the sea