Question

Trichodesmium erythraeum which gives colour to the red sea is a?
A. Green alga
B. Blue green alga
C. Red alga
D. Brown alga

Answer 1

Trichodesmium erythraeum are a species of cyanobacteria. They are pigmented. These pigments give the sea a red hue. This type of algae blooms and accumulates on the surface of the water.

Complete answer:
Trichodesmium erythraeum is also known as "sea sawdust”. Mitochondria are absent. It is capable of fixing nitrogen and secreting mucilage. Phycobiliproteins are present in thick-walled heterocysts. Gas vacuoles are present in the cell that forms around 60-70 percent of the total volume of cells and secretes mucilage. It is a cyanobacterium which is also known as blue-green alga
The red sea is named for the Trichodesmium erythraeum algae, an occasional explosion of cyanobacteria that accumulates and muddles the normally translucent blue-green waters. On the surface of these lakes, these cyanobacteria appear as red and pinkish mats. Trichodesmium erythraeum will die after flowering, and the sea will turn reddish-brown. During a "bloom" of cyanobacteria, the appearance of a body of water changes dramatically.
Trichodesmium erythraeum colonies are found floating on the surface of the water. With the naked eye, the alga is clearly visible and the body is filamentous, motile, and gram-negative. The blooms of this genus are poisonous to humans and other invertebrates. These could be several kilometers long and formed in the coastal area.
Therefore, option B, i.e., blue-green algae, is the correct choice.

Note: Cyanobacteria accounts for around half of the overall fixation of nitrogen in marine environments without the use of heterocysts under aerobic conditions during the daytime. This genus can live at low temperatures and in search of food, can move around 200 m deep into the sea.