In a freshwater marsh, the Gross Primary Production is $3000{\text{kJ,m}}^{-2}{\text{day}}^{-1}$. The ecological efficiency from producers to primary consumers is $9$ and from primary consumers to secondary consumers is $7$. How much energy per square metre per day is available to secondary consumers?

Step-by-step solution

1. Step 1: Compute energy reaching primary consumers – multiply GPP by $9$: $3000\times 0.09=270{\text{kJ,m}}^{-2}{\text{day}}^{-1}$, because 9% of the primary production is transferred to primary consumers.
2. Step 2: Compute energy reaching secondary consumers – multiply energy at primary consumers by $7$: $270\times 0.07=18.9{\text{kJ,m}}^{-2}{\text{day}}^{-1}$.
3. Step 3: State the result – the energy available to secondary consumers is $18.9{\text{kJ,m}}^{-2}{\text{day}}^{-1}$.

Concept tested: Energy transfer in food chains

Published 26 September 2026 · How this solution was prepared and checked