How is aquatic life benefitted by the fact that water has maximum density at 4°C?

At 4°C, water has its maximum density, 1g/cm³ or 1000 kg/m³, and minimum volume. Its density decreases as the temperature increases or decreases from this point. This enables marine life to exist in the colder regions of the world because even when the water freezes on the surface, it remains in liquid state below the ice layer as the density of water is greater than the density of ice and ice is a bad conductor of heat.