Question

how the anomalous expansion of water helps the existence of aquatic life

Answer 1

due to anamalous expansion, during winters, when twmp is below 0degree celcius,
only the top layer freezes thus saving the aquatic life
hope it helps!!

Answer 2

in polar region or in cold although the surface of water is covered with ice in winter season ..... in the bottom of the lake the temperature exist at 4°C. the different layers between top and bottom of layers are perform with different temperatures like 0°C at top and 1°C,2°C,3°C and at bottom it exist with 4°C due to anomalous behaviour of water. due to this behaviour aquatic animals will survive inside the lake.... the survival of animals exist.