Explanation:
They are often seen to form blooms in polluted waters.
The red sea is named so because of the colour of its water.This colour is due to the blooms formed by the cyanobacteria, Trichodesmium erythraeum, which accumulates and muddies the usually transparent water. They appear as a red and pinkish blanket on the surface of the waters. After blooming, the trichodesmium erythraeum die, and they turn the sea redish-brown.