Assertion: In a marine aquatic ecosystem, the biomass of phytoplanktons (producers) at any given time, is lower than the biomass of zooplanktons (primary consumers).
Reason: Phytoplanktons are consumed almost as rapidly as they are formed and thus have shorter life spans.

Step 1: Explain the concept of biomass in a marine aquatic ecosystem. \textbf{Solution}: Biomass refers to the total mass of living organisms in a given area or ecosystem. In a marine aquatic ecosystem, the biomass can be measured at different levels of the food chain. Step 2: Define the terms phytoplankton, zooplankton, and secondary consumers. \textbf{Solution}: Phytoplanktons are small, microscopic, free-floating aquatic plants that are the primary producers in an aquatic ecosystem. Zooplanktons are small, microscopic, free-floating aquatic animals that are the primary consumers in an aquatic ecosystem. Secondary consumers are organisms that feed on primary consumers. Step 3: Explain the relationship between the biomass of phytoplanktons, zooplanktons, and secondary consumers. \textbf{Solution}: In a marine aquatic ecosystem, the biomass of phytoplanktons is smaller than that of zooplanktons, and the biomass of zooplanktons is smaller than that of secondary consumers. This means that there are fewer phytoplanktons than zooplanktons, and fewer zooplanktons than secondary consumers. Step 4: Describe the inverted pyramid of biomass in an aquatic ecosystem. \textbf{Solution}: The inverted pyramid of biomass in an aquatic ecosystem refers to the shape of the biomass pyramid, where the biomass of producers (phytoplanktons) is smaller than that of primary consumers (zooplanktons), and the biomass of primary consumers is smaller than that of secondary consumers. This shape is the consequence of the very short life spans of phytoplanktons, which are consumed almost as rapidly as they are formed. Step 5: Summarize the key takeaways from the solutions. \textbf{Solution}: In a marine aquatic ecosystem, the biomass of producers (phytoplanktons) is smaller than that of primary consumers (zooplanktons), and the biomass of primary consumers is smaller than that of secondary consumers. This results in an inverted pyramid of biomass in an aquatic ecosystem, which is due to the short life spans of phytoplanktons.