4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.

Algal bloom
Algal bloom refers to an increase in the population of algae or blue-green algae in water, resulting in discoloration of the water body. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals.
Red tides are caused by red dinoflagellates (Gonyaulax) that multiply rapidly. Due to
their large numbers, the sea appears red in colour. They release large amounts of toxins in water that can cause death of a large number of fishes.