Question

Primary consumers or herbivores in aquatic ecosystem are

• A. Birds and mammals
• B. Molluscs
• C. Insects
• D. All of the above
  

Answer 1

The correct option is B Molluscs

Introduction to aquatic ecosystem :
An aquatic ecosystem is a water-based ecosystem. It includes communities inhabiting water and their interaction with the environment. Ponds, lakes, wetlands, rivers, and estuaries are some examples of aquatic ecosystems.

Primary consumers or herbivores :
Primary consumers or herbivores are organisms that are directly dependent on the producers for their food, i.e, they feed on the producers only.

Insects :
Aquatic insects feed on all possible food sources such as dead plant material, heterotrophic zooplanktons, dead remains of small animals, bacteria, fungi, etc.
Thus they are not necessarily primary consumers in a food chain and can occupy the trophic level of secondary consumers or carnivores too.

Birds and mammals :
Aquatic birds, large fishes and aquatic mammals feed on secondary consumers such as smaller fishes and insects which in turn feed on primary consumers such as zooplanktons, molluscs, small crustaceans, etc. Thus, the aquatic birds and mammals are tertiary consumers or the top carnivores and occupy the highest level in any aquatic food chain.

Molluscs :
Molluscs feed on photosynthetic algae or phytoplanktons present in the aquatic ecosystem. As they directly feed on the producers, they are considered to be the primary consumers or herbivores of an aquatic ecosystem.