Question

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

Answer 1

Blue green algae also named cyanobacteria and found in oceans. Blue-green algae have a blue pigment (C-phycocyanin) and a red pigment (C-phycoerythrin). These pigments give the red color to the sea. This alga form blooms and accumulates on the water surface.

Complete answer: General characters of this alga are –
-It is also known as “sea sawdust.”
-Protoplast is divisible into the chloroplast (pigmented region) and centroplast (non pigmented region).
-Mitochondria are absent.
-It is capable of nitrogen fixation and secretes mucilage.
-Thick walled heterocyst has phycobiliproteins.
-Gas vacuoles are present in the cell which forms about 60-70% of the total cell volume and can withstand high pressure.
-Colonies of Trichodesmium erythraeum are found floating on the water surface.
-This alga is being clearly visible with the naked eye and the body is filamentous, motile, and gram-negative.
Hence, the correct answer is option B i.e., Blue green alga.
Additional information:
The blooms of this genus are toxic to humans and other invertebrates. These may be several kilometers long and formed in the coastal region.

Note: It accounts for about half of the total nitrogen fixation in marine ecosystems under aerobic conditions during the daytime without using heterocyst. This genus can survive in low temperatures and can travel about 200m deep into the sea in search of food.