Why is the ecological pyramid of biomass in an open marine or aquatic ecosystem typically inverted?

Answer and explanation

Correct answer: D. Phytoplankton standing crop is small with rapid turnover to support larger zooplankton biomass

  1. Step 1: In an open aquatic ecosystem (e.g., oceans, deep lakes), primary producers are microscopic phytoplankton.
  2. Step 2: Phytoplankton have an extremely high turnover rate, they reproduce rapidly and have very short lifespans (days).
  3. Step 3: Consequently, the instantaneous standing crop biomass of phytoplankton measured at any single moment is small compared to the cumulative biomass of longer-lived, larger herbivores (zooplankton) and carnivores (fishes) supported by them.
  4. Step 4: Therefore, the pyramid of biomass in the sea shows a narrow base and broad upper levels (inverted pyramid).
Answer
Because the standing crop biomass of microscopic, rapidly reproducing phytoplankton at any given instant is much smaller than the biomass of long-lived zooplankton and fishes feeding on them
Why not the others: 'Because sunlight cannot penetrate water...' is false because the photic zone extends down to ~200 meters where phytoplankton thrive; 'Because marine fishes synthesize carbohydrates from salt...' is biologically impossible; 'Because decomposers outnumber producers...' does not determine the trophic biomass ratio of producers to primary consumers.

Practise more Organisms and Populations, Ecosystem, Biodiversity and Conservation.

Free questions with an explanation for every one, and full timed NEET UG mock tests.

All Organisms and Populations, Ecosystem, Biodiversity and Conservation questionsTake a mock test

More Organisms and Populations, Ecosystem, Biodiversity and Conservation questions