UPSC Prelims 2021 Question:

Consider the following kinds of organisms:

1. Copepods 
2. Cyanobacteria 
3. Diatoms 
4. Foraminifera
   
   

Which of the above are primary producers in the food chains of oceans?

Explanation:

• • Copepods: They are major secondary producers in the World Ocean. They represent an important link between phytoplankton, microzooplankton and higher trophic levels such as fish. So, point 1 is not correct.
    
    
  • Cyanobacteria: Green algae and cyanobacteria are found at the beginning of the food chain. They are known as primary producers because they make their own food. So, point 2 is correct.

• Diatoms: They are one of the major primary producers in the ocean, responsible annually for ~20% of photosynthetically fixed CO2 on Earth. In oceanic models, they are typically represented as large (>20 µm) microphytoplankton. So, point 3 is correct.
  
  

• Foraminifera: They are protozoans consisting of a single cell made up of protoplasm with one or more nuclei. They are heterotrophic protists that inhabit the marine sediments ranging from salt marshes and intertidal zones to deep-sea trenches and planktonic foraminifera occupying all open ocean surface waters. So, point 4 is not correct.
  
  

Therefore, option (2) is the correct answer.

Relevance: The bloom of Noctiluca Scintillans (sea sparkle) on the Karnataka coast has displaced microscopic algae called diatoms, which form the basis of the marine food chain.

Subject: Environment | Ecology