The pyramid of biomass in sea is generally inverted because:

The correct answer is Option (4) → the biomass of fishes far exceeds that of phytoplankton

A pyramid of biomass shows the mass of living matter at each trophic level. It is inverted when a higher level holds more biomass than the level below it.

Option (1) sunlight is filtered through sea water leading to less photosynthesis — Incorrect. Less light would lower production, but it does not explain why the upper level is bigger.

Option (2) of the high salt content of sea water — Incorrect. Salt content has nothing to do with the shape of the pyramid.

Option (3) the biomass of phytoplankton far exceeds that of fishes — Incorrect. The relation is reversed: if the producers had more biomass, the pyramid would be upright.

Option (4) the biomass of fishes far exceeds that of phytoplankton — Correct. Phytoplankton are small and short-lived but multiply fast, so at any time their standing biomass is less than that of the fishes they support.

Note: A similar question was also asked in CUET (UG) 2026 on 24-05-2026 (Slot 2) and on 21-05-2026 (Slot 1).

NCERT Extract:
Ecological Pyramids – “… In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level. There are exceptions to this generalisation: … The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton.”