Question

In an open ocean, the biomass of primary producers (microscopic algae) is often lower than the biomass of higher trophic levels (zooplanktons and fish), as illustrated below by an inverted pyramid of biomass. How can there be enough food in an open ocean to support the higher trophic levels?

• A. The microscopic primary producers are a source of food of high quality
• B. The microscopic primary producers have high rates of growth and reproduction
• C. The microscopic primary producers are less abundant
• D. The higher trophic levels are cold-blooded animals which do not require much food

Answer 1

Answer: (B)

In an open ocean, the large numbers of phytoplankton quickly complete their life cycles and sets of new population or crops of phytoplankton are formed every few hours or days. Thus, the cumulative energy contents that these generation after generation of phytoplankton trap in course of a year is certainly much more than trapped by only a few generations of herbivorous fishes in the corresponding time and space.