The amount of living organic matter is called biomass . And the pyramid of biomass is graphical representation of biomass per unit area at different tropic levels with producer at the base and carnivorous at the top .
The pyramid of biomass in ocean inverted because:
(i) Food chain in the ocean - {Phytoplankton → zooplankton → predatory fish.}
(ii) the biomass of zooplankton is greater than phytoplankton (the producer) because of their small size and low weight. The predatory fish is much larger than zooplankton.
(iii) the producer in ocean or aquatic ecosystem producers are phytoplankton have short life span and turn over and have lower mass than zooplankton.
(iv) the biomass of tropic level depends on the longevity of member