The biomass increases as we progress towards a higher trophic level. Thus pyramid of biomass is inverted in the aquatic ecosystem. The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton. Most pyramids are larger at the bottom, but marine biomass pyramids are often inverted. This is because the producers are very small and have limited mass. They also reproduce and die quickly, so there is less biomass at any given time compared to consumers.

Many river systems are disturbance dominated. Periphyton biomass can be reduced dramatically following high-water events and then regrows during inter-storm intervals. Similar resets are rare in terrestrial systems. In deeper lake systems, primary production is limited to the epilimnion. The detritus food chain on the other hand may not be inverted. Leaf fall provides the bulk of the food base for streams, ponds, and lakes, particularly in temperate deciduous habitats (my particular bias I must admit). Autumn biomass influx can far exceed that of the trophic layers above and persists long through the seasons.

I agree with Declan J Mccabe that biomass pyramids for some aquatic ecosystems are inverted because a small biomass of plankton with a high rate of reproduction and turnover can support a larger biomass of organisms with low rates of turnover at higher trophic levels. In a pond, as the producers (phytoplanktons) are small organisms, their biomass is least, and this value gradually shows an increase towards the apex of the pyramid, thus making the pyramid inverted in shape. Large fish consume small fish. The biomass increases as we progress towards a higher trophic level. Thus pyramid of biomass is inverted in the aquatic ecosystem. Pyramid of energy is always upright. As energy flows from one trophic level to the next trophic level some amount of energy is lost in each trophic level in the form of heat. Therefore, the pyramid of energy is always upright and can never be inverted. The biomass of phytoplankton is less as compared with that of the small herbivorous fish that feed on these producers. The biomass of large carnivorous fish that depends on small fishes is still greater. Therefore, the pyramid of biomass is inverted in pond ecosystem. In a pond or lake habitat, the biomass pyramid is inverted. The biomass of phytoplankton is lower than that of the small herbivorous fish that consume these producers. Large carnivorous fish that feed on small fish have higher biomass than small carnivorous fish. The pyramid of biomass in the aquatic ecosystem is inverted. Producers are present in less numbers in the aquatic ecosystem compared to consumers. In terrestrial ecosystems, energy and biomass pyramids are similar because biomass is closely associated with energy production. In aquatic ecosystems, the biomass pyramid may be inverted. The primary producers are phytoplankton with short life spans and high turnover.