Algal bloom refers to the excess growth of algae especially blue green algae in polluted water. Red tide refers to the red colour imparted to the sea water by the rapid multiplication of dinoflagellates like Gonyaulax. The toxins released by such large number of Gonyaulax may sometimes kill other marine animals such as fishes.
Thus, due to algal blooms and red tide, the animal life declines as these makes toxins and deficiency of oxygen inside water.