In what way is the anomalous behaviour of water advantageous to aquatic animals ?

Explanation

In cold countries and at polar region temperature falls below `0^(@) C` at winter . So surface of water will be frozen. Due to anomalous expansion of water even though the surface of lakes, and sea are frozen water will exist at bottom layers at `4^(@) C`.
Different layers in between ice and bottom will have different temperature likes `1C^(@)C, 2^(@)C or 3^(@)C`. In these layers aquatic animals are able to survive even in winter . Anomalous expansion of wateer helps for the survival of aquatic life at polar region and in cold countries.