Question

How is aquatic life benefited by the fact that water has maximum density at $4^{\circ }C$ ?

Answer 1

The density of water is approx. one gram per cubic centimeter. It is dependent on its temperature but the relation is not linear. When cooled from room temperature, liquid water becomes dense but at $4^{0}C$ pure water reaches its maximum density. As it is cooled it expands to become less dense. So the layer of ice floats on water as insulating layer. The warm layer settles at the bottom in winters and so aquatic life exists.